Merge branch 'master' into fix_26964

157 files changed, 1713 insertions, 539 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 96d0ad3b30..034e45b769 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,61 @@
+*   Notifications see frozen SQL string.
+
+    Fixes #23774.
+
+    *Richard Monette*
+
+*   RuntimeErrors are no longer translated to `ActiveRecord::StatementInvalid`.
+
+    *Richard Monette*
+
+*   Change the schema cache format to use YAML instead of Marshal.
+
+    *Kir Shatrov*
+
+*   Support index length and order options using both string and symbol
+    column names.
+
+    Fixes #27243.
+
+    *Ryuta Kamizono*
+
+*   Raise `ActiveRecord::RangeError` when values that executed are out of range.
+
+    *Ryuta Kamizono*
+
+*   Raise `ActiveRecord::NotNullViolation` when a record cannot be inserted
+    or updated because it would violate a not null constraint.
+
+    *Ryuta Kamizono*
+
+*   Emulate db trigger behaviour for after_commit :destroy, :update.
+
+    Race conditions can occur when an ActiveRecord is destroyed
+    twice or destroyed and updated. The callbacks should only be
+    triggered once, similar to a SQL database trigger.
+
+    *Stefan Budeanu*
+
+*   Moved `DecimalWithoutScale`, `Text`, and `UnsignedInteger` from Active Model to Active Record.
+
+    *Iain Beeston*
+
+*   Fix `write_attribute` method to check whether an attribute is aliased or not, and
+    use the aliased attribute name if needed.
+
+    *Prathamesh Sonpatki*
+
+*   Fix `read_attribute` method to check whether an attribute is aliased or not, and
+    use the aliased attribute name if needed.
+
+    Fixes #26417.
+
+    *Prathamesh Sonpatki*
+
+*   PostgreSQL & MySQL: Use big integer as primary key type for new tables.
+
+    *Jon McCartie*, *Pavel Pravosud*
+
 *   Change the type argument of `ActiveRecord::Base#attribute` to be optional.
     The default is now `ActiveRecord::Type::Value.new`, which provides no type
     casting behavior.
@@ -14,7 +72,7 @@
 
     *Sergey Alekseev*
 
-*   Raise ActiveRecord::RecordNotFound from collection `*_ids` setters
+*   Raise `ActiveRecord::RecordNotFound` from collection `*_ids` setters
     for unknown IDs with a better error message.
 
     Changes the collection `*_ids` setters to cast provided IDs the data
@@ -54,7 +112,7 @@
 
     *Jon Moss*
 
-*   Added `stat` method to `ActiveRecord::ConnectionAdapters::ConnectionPool`
+*   Added `stat` method to `ActiveRecord::ConnectionAdapters::ConnectionPool`.
 
     Example:
 
@@ -101,7 +159,7 @@
 
 *   Fixed: Optimistic locking does not work well with `null` in the database.
 
-    Fixes #26024
+    Fixes #26024.
 
     *bogdanvlviv*
 
@@ -110,7 +168,7 @@
 
     *Edho Arief*
 
-*   Serialize JSON attribute value `nil` as SQL `NULL`, not JSON `null`
+*   Serialize JSON attribute value `nil` as SQL `NULL`, not JSON `null`.
 
     *Trung Duc Tran*
 
@@ -214,7 +272,7 @@
     successfully rolled back when the column was given and invalid column
     type.
 
-    Fixes #26087
+    Fixes #26087.
 
     *Travis O'Neill*
 
@@ -244,7 +302,7 @@
     *Takeshi Akima*
 
 *   Virtual attributes will no longer raise when read on models loaded from the
-    database
+    database.
 
     *Sean Griffin*
 
diff --git a/activerecord/lib/active_record/aggregations.rb b/activerecord/lib/active_record/aggregations.rb
index 08dfc3a64f..10cbd5429c 100644
--- a/activerecord/lib/active_record/aggregations.rb
+++ b/activerecord/lib/active_record/aggregations.rb
@@ -15,11 +15,11 @@ module ActiveRecord
 
     private
 
-      def clear_aggregation_cache # :nodoc:
+      def clear_aggregation_cache
         @aggregation_cache.clear if persisted?
       end
 
-      def init_internals # :nodoc:
+      def init_internals
         @aggregation_cache = {}
         super
       end
diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 19308643f3..7eb008fc27 100644
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -260,11 +260,11 @@ module ActiveRecord
 
     private
       # Clears out the association cache.
-      def clear_association_cache # :nodoc:
+      def clear_association_cache
         @association_cache.clear if persisted?
       end
 
-      def init_internals # :nodoc:
+      def init_internals
         @association_cache = {}
         super
       end
diff --git a/activerecord/lib/active_record/associations/association_scope.rb b/activerecord/lib/active_record/associations/association_scope.rb
index 12f8c1ccd4..c6d204d3c2 100644
--- a/activerecord/lib/active_record/associations/association_scope.rb
+++ b/activerecord/lib/active_record/associations/association_scope.rb
@@ -49,6 +49,8 @@ module ActiveRecord
         binds
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
       protected
 
         attr_reader :value_transformation
diff --git a/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb b/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb
index 42a90b449c..6b71826431 100644
--- a/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb
+++ b/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb
@@ -78,9 +78,9 @@ module ActiveRecord::Associations::Builder # :nodoc:
 
         private
 
-        def self.suppress_composite_primary_key(pk)
-          pk unless pk.is_a?(Array)
-        end
+          def self.suppress_composite_primary_key(pk)
+            pk unless pk.is_a?(Array)
+          end
       }
 
       join_model.name                = "HABTM_#{association_name.to_s.camelize}"
diff --git a/activerecord/lib/active_record/associations/collection_association.rb b/activerecord/lib/active_record/associations/collection_association.rb
index 3d23fa1e46..13f77c7d4d 100644
--- a/activerecord/lib/active_record/associations/collection_association.rb
+++ b/activerecord/lib/active_record/associations/collection_association.rb
@@ -75,7 +75,7 @@ module ActiveRecord
           r.send(reflection.association_primary_key)
         end.values_at(*ids).compact
         if records.size != ids.size
-          scope.raise_record_not_found_exception!(ids, records.size, ids.size, reflection.association_primary_key)
+          klass.all.raise_record_not_found_exception!(ids, records.size, ids.size, reflection.association_primary_key)
         else
           replace(records)
         end
@@ -299,12 +299,23 @@ module ActiveRecord
       def replace_on_target(record, index, skip_callbacks)
         callback(:before_add, record) unless skip_callbacks
 
-        yield(record) if block_given?
+        begin
+          if index
+            record_was = target[index]
+            target[index] = record
+          else
+            target << record
+          end
 
-        if index
-          @target[index] = record
-        else
-          append_record(record)
+          yield(record) if block_given?
+        rescue
+          if index
+            target[index] = record_was
+          else
+            target.delete(record)
+          end
+
+          raise
         end
 
         callback(:after_add, record) unless skip_callbacks
@@ -502,10 +513,6 @@ module ActiveRecord
             load_target.select { |r| ids.include?(r.id.to_s) }
           end
         end
-
-        def append_record(record)
-          @target << record unless @target.include?(record)
-        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/associations/collection_proxy.rb b/activerecord/lib/active_record/associations/collection_proxy.rb
index 35a98d7090..0d84805b4d 100644
--- a/activerecord/lib/active_record/associations/collection_proxy.rb
+++ b/activerecord/lib/active_record/associations/collection_proxy.rb
@@ -1126,7 +1126,7 @@ module ActiveRecord
         self
       end
 
-      protected
+      private
 
         def find_nth_with_limit(index, limit)
           load_target if find_from_target?
@@ -1138,8 +1138,6 @@ module ActiveRecord
           super
         end
 
-      private
-
         def null_scope?
           @association.null_scope?
         end
diff --git a/activerecord/lib/active_record/associations/has_many_through_association.rb b/activerecord/lib/active_record/associations/has_many_through_association.rb
index 8c90aea975..c4a7fe4432 100644
--- a/activerecord/lib/active_record/associations/has_many_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -38,10 +38,12 @@ module ActiveRecord
       def insert_record(record, validate = true, raise = false)
         ensure_not_nested
 
-        if raise
-          record.save!(validate: validate)
-        else
-          return unless record.save(validate: validate)
+        if record.new_record? || record.has_changes_to_save?
+          if raise
+            record.save!(validate: validate)
+          else
+            return unless record.save(validate: validate)
+          end
         end
 
         save_through_record(record)
@@ -206,10 +208,6 @@ module ActiveRecord
         def invertible_for?(record)
           false
         end
-
-        def append_record(record)
-          @target << record
-        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/associations/singular_association.rb b/activerecord/lib/active_record/associations/singular_association.rb
index 1953cc6a72..ee7b7c8bea 100644
--- a/activerecord/lib/active_record/associations/singular_association.rb
+++ b/activerecord/lib/active_record/associations/singular_association.rb
@@ -58,6 +58,8 @@ module ActiveRecord
           sc.execute(binds, klass, conn) do |record|
             set_inverse_instance record
           end.first
+        rescue ::RangeError
+          nil
         end
 
         def replace(record)
diff --git a/activerecord/lib/active_record/associations/through_association.rb b/activerecord/lib/active_record/associations/through_association.rb
index f4129edc5a..6b87993ba3 100644
--- a/activerecord/lib/active_record/associations/through_association.rb
+++ b/activerecord/lib/active_record/associations/through_association.rb
@@ -4,7 +4,7 @@ module ActiveRecord
     module ThroughAssociation #:nodoc:
       delegate :source_reflection, :through_reflection, to: :reflection
 
-      protected
+      private
 
         # We merge in these scopes for two reasons:
         #
@@ -21,8 +21,6 @@ module ActiveRecord
           scope
         end
 
-      private
-
         # Construct attributes for :through pointing to owner and associate. This is used by the
         # methods which create and delete records on the association.
         #
diff --git a/activerecord/lib/active_record/attribute.rb b/activerecord/lib/active_record/attribute.rb
index 0b08c2a39b..38281158d8 100644
--- a/activerecord/lib/active_record/attribute.rb
+++ b/activerecord/lib/active_record/attribute.rb
@@ -128,11 +128,22 @@ module ActiveRecord
       coder["value"] = value if defined?(@value)
     end
 
+    # TODO Change this to private once we've dropped Ruby 2.2 support.
+    # Workaround for Ruby 2.2 "private attribute?" warning.
     protected
 
       attr_reader :original_attribute
       alias_method :assigned?, :original_attribute
 
+      def original_value_for_database
+        if assigned?
+          original_attribute.original_value_for_database
+        else
+          _original_value_for_database
+        end
+      end
+
+    private
       def initialize_dup(other)
         if defined?(@value) && @value.duplicable?
           @value = @value.dup
@@ -143,14 +154,6 @@ module ActiveRecord
         assigned? && type.changed?(original_value, value, value_before_type_cast)
       end
 
-      def original_value_for_database
-        if assigned?
-          original_attribute.original_value_for_database
-        else
-          _original_value_for_database
-        end
-      end
-
       def _original_value_for_database
         type.serialize(original_value)
       end
diff --git a/activerecord/lib/active_record/attribute/user_provided_default.rb b/activerecord/lib/active_record/attribute/user_provided_default.rb
index a4e2c2ec85..57f8bbed76 100644
--- a/activerecord/lib/active_record/attribute/user_provided_default.rb
+++ b/activerecord/lib/active_record/attribute/user_provided_default.rb
@@ -20,6 +20,8 @@ module ActiveRecord
         self.class.new(name, user_provided_value, type, original_attribute)
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
       protected
 
         attr_reader :user_provided_value
diff --git a/activerecord/lib/active_record/attribute_assignment.rb b/activerecord/lib/active_record/attribute_assignment.rb
index 9843e0ca66..d0dfca0cac 100644
--- a/activerecord/lib/active_record/attribute_assignment.rb
+++ b/activerecord/lib/active_record/attribute_assignment.rb
@@ -12,7 +12,7 @@ module ActiveRecord
 
     private
 
-      def _assign_attributes(attributes) # :nodoc:
+      def _assign_attributes(attributes)
         multi_parameter_attributes  = {}
         nested_parameter_attributes = {}
 
diff --git a/activerecord/lib/active_record/attribute_decorators.rb b/activerecord/lib/active_record/attribute_decorators.rb
index 340dfe11cf..c39e9ce4c5 100644
--- a/activerecord/lib/active_record/attribute_decorators.rb
+++ b/activerecord/lib/active_record/attribute_decorators.rb
@@ -8,12 +8,34 @@ module ActiveRecord
     end
 
     module ClassMethods # :nodoc:
+      # This method is an internal API used to create class macros such as
+      # +serialize+, and features like time zone aware attributes.
+      #
+      # Used to wrap the type of an attribute in a new type.
+      # When the schema for a model is loaded, attributes with the same name as
+      # +column_name+ will have their type yielded to the given block. The
+      # return value of that block will be used instead.
+      #
+      # Subsequent calls where +column_name+ and +decorator_name+ are the same
+      # will override the previous decorator, not decorate twice. This can be
+      # used to create idempotent class macros like +serialize+
       def decorate_attribute_type(column_name, decorator_name, &block)
         matcher = ->(name, _) { name == column_name.to_s }
         key = "_#{column_name}_#{decorator_name}"
         decorate_matching_attribute_types(matcher, key, &block)
       end
 
+      # This method is an internal API used to create higher level features like
+      # time zone aware attributes.
+      #
+      # When the schema for a model is loaded, +matcher+ will be called for each
+      # attribute with its name and type. If the matcher returns a truthy value,
+      # the type will then be yielded to the given block, and the return value
+      # of that block will replace the type.
+      #
+      # Subsequent calls to this method with the same value for +decorator_name+
+      # will replace the previous decorator, not decorate twice. This can be
+      # used to ensure that class macros are idempotent.
       def decorate_matching_attribute_types(matcher, decorator_name, &block)
         reload_schema_from_cache
         decorator_name = decorator_name.to_s
diff --git a/activerecord/lib/active_record/attribute_methods/primary_key.rb b/activerecord/lib/active_record/attribute_methods/primary_key.rb
index 287367f92a..8fcac82a0d 100644
--- a/activerecord/lib/active_record/attribute_methods/primary_key.rb
+++ b/activerecord/lib/active_record/attribute_methods/primary_key.rb
@@ -50,7 +50,7 @@ module ActiveRecord
         attribute_in_database(self.class.primary_key)
       end
 
-      protected
+      private
 
         def attribute_method?(attr_name)
           attr_name == "id" || super
diff --git a/activerecord/lib/active_record/attribute_methods/read.rb b/activerecord/lib/active_record/attribute_methods/read.rb
index 30f7750884..369a6e35aa 100644
--- a/activerecord/lib/active_record/attribute_methods/read.rb
+++ b/activerecord/lib/active_record/attribute_methods/read.rb
@@ -4,7 +4,7 @@ module ActiveRecord
       extend ActiveSupport::Concern
 
       module ClassMethods
-        protected
+        private
 
           # We want to generate the methods via module_eval rather than
           # define_method, because define_method is slower on dispatch.
@@ -48,7 +48,12 @@ module ActiveRecord
       # it has been typecast (for example, "2004-12-12" in a date column is cast
       # to a date object, like Date.new(2004, 12, 12)).
       def read_attribute(attr_name, &block)
-        name = attr_name.to_s
+        name = if self.class.attribute_alias?(attr_name)
+          self.class.attribute_alias(attr_name).to_s
+        else
+          attr_name.to_s
+        end
+
         name = self.class.primary_key if name == "id".freeze
         _read_attribute(name, &block)
       end
diff --git a/activerecord/lib/active_record/attribute_methods/write.rb b/activerecord/lib/active_record/attribute_methods/write.rb
index f65c297e01..fe0e01db28 100644
--- a/activerecord/lib/active_record/attribute_methods/write.rb
+++ b/activerecord/lib/active_record/attribute_methods/write.rb
@@ -8,7 +8,7 @@ module ActiveRecord
       end
 
       module ClassMethods
-        protected
+        private
 
           def define_method_attribute=(name)
             safe_name = name.unpack("h*".freeze).first
@@ -29,7 +29,13 @@ module ActiveRecord
       # specified +value+. Empty strings for Integer and Float columns are
       # turned into +nil+.
       def write_attribute(attr_name, value)
-        write_attribute_with_type_cast(attr_name, value, true)
+        name = if self.class.attribute_alias?(attr_name)
+          self.class.attribute_alias(attr_name).to_s
+        else
+          attr_name.to_s
+        end
+
+        write_attribute_with_type_cast(name, value, true)
       end
 
       def raw_write_attribute(attr_name, value) # :nodoc:
diff --git a/activerecord/lib/active_record/attribute_mutation_tracker.rb b/activerecord/lib/active_record/attribute_mutation_tracker.rb
index db86b2b294..3417090830 100644
--- a/activerecord/lib/active_record/attribute_mutation_tracker.rb
+++ b/activerecord/lib/active_record/attribute_mutation_tracker.rb
@@ -60,6 +60,8 @@ module ActiveRecord
       forced_changes << attr_name.to_s
     end
 
+    # TODO Change this to private once we've dropped Ruby 2.2 support.
+    # Workaround for Ruby 2.2 "private attribute?" warning.
     protected
 
       attr_reader :attributes, :forced_changes
diff --git a/activerecord/lib/active_record/attribute_set.rb b/activerecord/lib/active_record/attribute_set.rb
index 5bde1f107c..66b278219a 100644
--- a/activerecord/lib/active_record/attribute_set.rb
+++ b/activerecord/lib/active_record/attribute_set.rb
@@ -98,6 +98,8 @@ module ActiveRecord
       attributes == other.attributes
     end
 
+    # TODO Change this to private once we've dropped Ruby 2.2 support.
+    # Workaround for Ruby 2.2 "private attribute?" warning.
     protected
 
       attr_reader :attributes
diff --git a/activerecord/lib/active_record/attribute_set/builder.rb b/activerecord/lib/active_record/attribute_set/builder.rb
index 661f996e1a..2f624d32af 100644
--- a/activerecord/lib/active_record/attribute_set/builder.rb
+++ b/activerecord/lib/active_record/attribute_set/builder.rb
@@ -90,6 +90,8 @@ module ActiveRecord
       @materialized = true
     end
 
+    # TODO Change this to private once we've dropped Ruby 2.2 support.
+    # Workaround for Ruby 2.2 "private attribute?" warning.
     protected
 
       attr_reader :types, :values, :additional_types, :delegate_hash, :default
diff --git a/activerecord/lib/active_record/attribute_set/yaml_encoder.rb b/activerecord/lib/active_record/attribute_set/yaml_encoder.rb
index c86cfc4263..899de14792 100644
--- a/activerecord/lib/active_record/attribute_set/yaml_encoder.rb
+++ b/activerecord/lib/active_record/attribute_set/yaml_encoder.rb
@@ -31,6 +31,8 @@ module ActiveRecord
         end
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
       protected
 
         attr_reader :default_types
diff --git a/activerecord/lib/active_record/autosave_association.rb b/activerecord/lib/active_record/autosave_association.rb
index b343332bae..9d0b501862 100644
--- a/activerecord/lib/active_record/autosave_association.rb
+++ b/activerecord/lib/active_record/autosave_association.rb
@@ -383,6 +383,9 @@ module ActiveRecord
         if association = association_instance_get(reflection.name)
           autosave = reflection.options[:autosave]
 
+          # reconstruct the scope now that we know the owner's id
+          association.reset_scope if association.respond_to?(:reset_scope)
+
           if records = associated_records_to_validate_or_save(association, @new_record_before_save, autosave)
             if autosave
               records_to_destroy = records.select(&:marked_for_destruction?)
@@ -408,9 +411,6 @@ module ActiveRecord
               raise ActiveRecord::Rollback unless saved
             end
           end
-
-          # reconstruct the scope now that we know the owner's id
-          association.reset_scope if association.respond_to?(:reset_scope)
         end
       end
 
diff --git a/activerecord/lib/active_record/callbacks.rb b/activerecord/lib/active_record/callbacks.rb
index f2e3912c6e..be6720ddf3 100644
--- a/activerecord/lib/active_record/callbacks.rb
+++ b/activerecord/lib/active_record/callbacks.rb
@@ -283,15 +283,15 @@ module ActiveRecord
 
   private
 
-    def create_or_update(*) #:nodoc:
+    def create_or_update(*)
       _run_save_callbacks { super }
     end
 
-    def _create_record #:nodoc:
+    def _create_record
       _run_create_callbacks { super }
     end
 
-    def _update_record(*) #:nodoc:
+    def _update_record(*)
       _run_update_callbacks { super }
     end
   end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
index faccd1d641..e444cec72b 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
@@ -10,9 +10,9 @@ module ActiveRecord
       def to_sql(arel, binds = [])
         if arel.respond_to?(:ast)
           collected = visitor.accept(arel.ast, collector)
-          collected.compile(binds, self)
+          collected.compile(binds, self).freeze
         else
-          arel
+          arel.dup.freeze
         end
       end
 
@@ -360,7 +360,7 @@ module ActiveRecord
       end
       alias join_to_delete join_to_update
 
-      protected
+      private
 
         # Returns a subquery for the given key using the join information.
         def subquery_for(key, select)
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
index 83d1d7cd01..9b324c090b 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
@@ -71,7 +71,7 @@ module ActiveRecord
         polymorphic: false,
         index: true,
         foreign_key: false,
-        type: :integer,
+        type: :bigint,
         **options
       )
         @name = name
@@ -100,6 +100,8 @@ module ActiveRecord
         end
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
       protected
 
         attr_reader :name, :polymorphic, :index, :foreign_key, :type, :options
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb
index dabccc00bb..b912d24626 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb
@@ -56,7 +56,7 @@ module ActiveRecord
       private
 
         def default_primary_key?(column)
-          schema_type(column) == :integer
+          schema_type(column) == :bigint
         end
 
         def schema_type(column)
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index 151629b02a..9c820ce585 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -996,15 +996,13 @@ module ActiveRecord
       def insert_versions_sql(versions) # :nodoc:
         sm_table = ActiveRecord::Migrator.schema_migrations_table_name
 
-        if supports_multi_insert?
+        if versions.is_a?(Array)
           sql = "INSERT INTO #{sm_table} (version) VALUES\n"
           sql << versions.map { |v| "('#{v}')" }.join(",\n")
           sql << ";\n\n"
           sql
         else
-          versions.map { |version|
-            "INSERT INTO #{sm_table} (version) VALUES ('#{version}');"
-          }.join "\n\n"
+          "INSERT INTO #{sm_table} (version) VALUES ('#{versions}');"
         end
       end
 
@@ -1042,7 +1040,13 @@ module ActiveRecord
           if (duplicate = inserting.detect { |v| inserting.count(v) > 1 })
             raise "Duplicate migration #{duplicate}. Please renumber your migrations to resolve the conflict."
           end
-          execute insert_versions_sql(inserting)
+          if supports_multi_insert?
+            execute insert_versions_sql(inserting)
+          else
+            inserting.each do |v|
+              execute insert_versions_sql(v)
+            end
+          end
         end
       end
 
@@ -1165,12 +1169,13 @@ module ActiveRecord
         raise NotImplementedError, "#{self.class} does not support changing column comments"
       end
 
-      protected
+      private
 
         def add_index_sort_order(quoted_columns, **options)
           if order = options[:order]
             case order
             when Hash
+              order = order.symbolize_keys
               quoted_columns.each { |name, column| column << " #{order[name].upcase}" if order[name].present? }
             when String
               quoted_columns.each { |name, column| column << " #{order.upcase}" if order.present? }
@@ -1248,7 +1253,6 @@ module ActiveRecord
           end
         end
 
-      private
         def create_table_definition(*args)
           TableDefinition.new(*args)
         end
@@ -1257,7 +1261,7 @@ module ActiveRecord
           AlterTable.new create_table_definition(name)
         end
 
-        def index_name_options(column_names) # :nodoc:
+        def index_name_options(column_names)
           if column_names.is_a?(String)
             column_names = column_names.scan(/\w+/).join("_")
           end
@@ -1265,7 +1269,7 @@ module ActiveRecord
           { column: column_names }
         end
 
-        def foreign_key_name(table_name, options) # :nodoc:
+        def foreign_key_name(table_name, options)
           identifier = "#{table_name}_#{options.fetch(:column)}_fk"
           hashed_identifier = Digest::SHA256.hexdigest(identifier).first(10)
           options.fetch(:name) do
@@ -1273,7 +1277,7 @@ module ActiveRecord
           end
         end
 
-        def validate_index_length!(table_name, new_name, internal = false) # :nodoc:
+        def validate_index_length!(table_name, new_name, internal = false)
           max_index_length = internal ? index_name_length : allowed_index_name_length
 
           if new_name.length > max_index_length
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 237367c8b3..4046b3829d 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -499,9 +499,9 @@ module ActiveRecord
         result
       end
 
-      protected
+      private
 
-        def initialize_type_map(m) # :nodoc:
+        def initialize_type_map(m)
           register_class_with_limit m, %r(boolean)i,       Type::Boolean
           register_class_with_limit m, %r(char)i,          Type::String
           register_class_with_limit m, %r(binary)i,        Type::Binary
@@ -532,37 +532,37 @@ module ActiveRecord
           end
         end
 
-        def reload_type_map # :nodoc:
+        def reload_type_map
           type_map.clear
           initialize_type_map(type_map)
         end
 
-        def register_class_with_limit(mapping, key, klass) # :nodoc:
+        def register_class_with_limit(mapping, key, klass)
           mapping.register_type(key) do |*args|
             limit = extract_limit(args.last)
             klass.new(limit: limit)
           end
         end
 
-        def register_class_with_precision(mapping, key, klass) # :nodoc:
+        def register_class_with_precision(mapping, key, klass)
           mapping.register_type(key) do |*args|
             precision = extract_precision(args.last)
             klass.new(precision: precision)
           end
         end
 
-        def extract_scale(sql_type) # :nodoc:
+        def extract_scale(sql_type)
           case sql_type
           when /\((\d+)\)/ then 0
           when /\((\d+)(,(\d+))\)/ then $3.to_i
           end
         end
 
-        def extract_precision(sql_type) # :nodoc:
+        def extract_precision(sql_type)
           $1.to_i if sql_type =~ /\((\d+)(,\d+)?\)/
         end
 
-        def extract_limit(sql_type) # :nodoc:
+        def extract_limit(sql_type)
           case sql_type
           when /^bigint/i
             8
@@ -583,7 +583,7 @@ module ActiveRecord
           exception
         end
 
-        def log(sql, name = "SQL", binds = [], type_casted_binds = [], statement_name = nil)
+        def log(sql, name = "SQL", binds = [], type_casted_binds = [], statement_name = nil) # :doc:
           @instrumenter.instrument(
             "sql.active_record",
             sql:               sql,
@@ -598,14 +598,19 @@ module ActiveRecord
 
         def translate_exception(exception, message)
           # override in derived class
-          ActiveRecord::StatementInvalid.new(message)
+          case exception
+          when RuntimeError
+            exception
+          else
+            ActiveRecord::StatementInvalid.new(message)
+          end
         end
 
         def without_prepared_statement?(binds)
           !prepared_statements || binds.empty?
         end
 
-        def column_for(table_name, column_name) # :nodoc:
+        def column_for(table_name, column_name)
           column_name = column_name.to_s
           columns(table_name).detect { |c| c.name == column_name } ||
             raise(ActiveRecordError, "No such column: #{table_name}.#{column_name}")
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 98152853c2..20fcac8a22 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -39,7 +39,7 @@ module ActiveRecord
       self.emulate_booleans = true
 
       NATIVE_DATABASE_TYPES = {
-        primary_key: "int auto_increment PRIMARY KEY",
+        primary_key: "bigint auto_increment PRIMARY KEY",
         string:      { name: "varchar", limit: 255 },
         text:        { name: "text", limit: 65535 },
         integer:     { name: "int", limit: 4 },
@@ -649,9 +649,9 @@ module ActiveRecord
         !native_database_types[type].nil?
       end
 
-      protected
+      private
 
-        def initialize_type_map(m) # :nodoc:
+        def initialize_type_map(m)
           super
 
           register_class_with_limit m, %r(char)i, MysqlString
@@ -691,7 +691,7 @@ module ActiveRecord
           end
         end
 
-        def register_integer_type(mapping, key, options) # :nodoc:
+        def register_integer_type(mapping, key, options)
           mapping.register_type(key) do |sql_type|
             if /\bunsigned\b/.match?(sql_type)
               Type::UnsignedInteger.new(options)
@@ -717,6 +717,7 @@ module ActiveRecord
           if length = options[:length]
             case length
             when Hash
+              length = length.symbolize_keys
               quoted_columns.each { |name, column| column << "(#{length[name]})" if length[name].present? }
             when Integer
               quoted_columns.each { |name, column| column << "(#{length})" }
@@ -733,9 +734,14 @@ module ActiveRecord
 
         # See https://dev.mysql.com/doc/refman/5.7/en/error-messages-server.html
         ER_DUP_ENTRY            = 1062
+        ER_NOT_NULL_VIOLATION   = 1048
+        ER_DO_NOT_HAVE_DEFAULT  = 1364
         ER_NO_REFERENCED_ROW_2  = 1452
         ER_DATA_TOO_LONG        = 1406
+        ER_OUT_OF_RANGE         = 1264
         ER_LOCK_DEADLOCK        = 1213
+        ER_CANNOT_ADD_FOREIGN   = 1215
+        ER_CANNOT_CREATE_TABLE  = 1005
 
         def translate_exception(exception, message)
           case error_number(exception)
@@ -743,8 +749,20 @@ module ActiveRecord
             RecordNotUnique.new(message)
           when ER_NO_REFERENCED_ROW_2
             InvalidForeignKey.new(message)
+          when ER_CANNOT_ADD_FOREIGN
+            mismatched_foreign_key(message)
+          when ER_CANNOT_CREATE_TABLE
+            if message.include?("errno: 150")
+              mismatched_foreign_key(message)
+            else
+              super
+            end
           when ER_DATA_TOO_LONG
             ValueTooLong.new(message)
+          when ER_OUT_OF_RANGE
+            RangeError.new(message)
+          when ER_NOT_NULL_VIOLATION, ER_DO_NOT_HAVE_DEFAULT
+            NotNullViolation.new(message)
           when ER_LOCK_DEADLOCK
             Deadlocked.new(message)
           else
@@ -769,6 +787,10 @@ module ActiveRecord
             options[:null] = column.null
           end
 
+          unless options.key?(:comment)
+            options[:comment] = column.comment
+          end
+
           td = create_table_definition(table_name)
           cd = td.new_column_definition(column.name, type, options)
           schema_creation.accept(ChangeColumnDefinition.new(cd, column.name))
@@ -815,8 +837,6 @@ module ActiveRecord
           [remove_column_sql(table_name, :updated_at), remove_column_sql(table_name, :created_at)]
         end
 
-      private
-
         # MySQL is too stupid to create a temporary table for use subquery, so we have
         # to give it some prompting in the form of a subsubquery. Ugh!
         def subquery_for(key, select)
@@ -886,7 +906,7 @@ module ActiveRecord
           end.compact.join(", ")
 
           # ...and send them all in one query
-          @connection.query "SET #{encoding} #{sql_mode_assignment} #{variable_assignments}"
+          execute "SET #{encoding} #{sql_mode_assignment} #{variable_assignments}"
         end
 
         def column_definitions(table_name) # :nodoc:
@@ -910,6 +930,18 @@ module ActiveRecord
           MySQL::TableDefinition.new(*args)
         end
 
+        def mismatched_foreign_key(message)
+          parts = message.scan(/`(\w+)`[ $)]/).flatten
+          MismatchedForeignKey.new(
+            self,
+            message: message,
+            table: parts[0],
+            foreign_key: parts[1],
+            target_table: parts[2],
+            primary_key: parts[3],
+          )
+        end
+
         def extract_schema_qualified_name(string) # :nodoc:
           schema, name = string.to_s.scan(/[^`.\s]+|`[^`]*`/)
           schema, name = @config[:database], schema unless name
diff --git a/activerecord/lib/active_record/connection_adapters/column.rb b/activerecord/lib/active_record/connection_adapters/column.rb
index 02d546209d..61cd7ae4cc 100644
--- a/activerecord/lib/active_record/connection_adapters/column.rb
+++ b/activerecord/lib/active_record/connection_adapters/column.rb
@@ -40,6 +40,28 @@ module ActiveRecord
         Base.human_attribute_name(@name)
       end
 
+      def init_with(coder)
+        @name = coder["name"]
+        @table_name = coder["table_name"]
+        @sql_type_metadata = coder["sql_type_metadata"]
+        @null = coder["null"]
+        @default = coder["default"]
+        @default_function = coder["default_function"]
+        @collation = coder["collation"]
+        @comment = coder["comment"]
+      end
+
+      def encode_with(coder)
+        coder["name"] = @name
+        coder["table_name"] = @table_name
+        coder["sql_type_metadata"] = @sql_type_metadata
+        coder["null"] = @null
+        coder["default"] = @default
+        coder["default_function"] = @default_function
+        coder["collation"] = @collation
+        coder["comment"] = @comment
+      end
+
       def ==(other)
         other.is_a?(Column) &&
           attributes_for_hash == other.attributes_for_hash
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/column.rb b/activerecord/lib/active_record/connection_adapters/mysql/column.rb
index 22b9df5309..1499c1681f 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/column.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/column.rb
@@ -5,7 +5,7 @@ module ActiveRecord
         delegate :extra, to: :sql_type_metadata, allow_nil: true
 
         def unsigned?
-          !/\A(?:enum|set)\b/.match?(sql_type) && /\bunsigned\b/.match?(sql_type)
+          /\bunsigned(?: zerofill)?\z/.match?(sql_type)
         end
 
         def case_sensitive?
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb b/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb
index c7098105a8..78e7181266 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb
@@ -52,14 +52,12 @@ module ActiveRecord
         end
         alias :exec_update :exec_delete
 
-        protected
+        private
 
           def last_inserted_id(result)
             @connection.last_id
           end
 
-        private
-
           def select_result(sql, name = nil, binds = [])
             if without_prepared_statement?(binds)
               execute_and_free(sql, name) { |result| yield result }
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/mysql/schema_definitions.rb
index ce773ed75b..0cf40de70f 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_definitions.rb
@@ -3,7 +3,10 @@ module ActiveRecord
     module MySQL
       module ColumnMethods
         def primary_key(name, type = :primary_key, **options)
-          options[:auto_increment] = true if type == :bigint && !options.key?(:default)
+          if type == :primary_key && !options.key?(:default)
+            options[:auto_increment] = true
+            options[:limit] = 8
+          end
           super
         end
 
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb b/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb
index 9b02d8a34b..2065816501 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb
@@ -3,11 +3,9 @@ module ActiveRecord
     module MySQL
       module ColumnDumper
         def column_spec_for_primary_key(column)
-          if column.bigint?
-            spec = { id: :bigint.inspect }
-            spec[:default] = schema_default(column) || "nil" unless column.auto_increment?
-          else
-            spec = super
+          spec = super
+          if column.type == :integer && !column.auto_increment?
+            spec[:default] = schema_default(column) || "nil"
           end
           spec[:unsigned] = "true" if column.unsigned?
           spec
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/bit.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/bit.rb
index 302d393277..0a505f46a7 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/bit.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/bit.rb
@@ -41,6 +41,8 @@ module ActiveRecord
               /\A[0-9A-F]*\Z/i.match?(value)
             end
 
+            # TODO Change this to private once we've dropped Ruby 2.2 support.
+            # Workaround for Ruby 2.2 "private attribute?" warning.
             protected
 
               attr_reader :value
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
index ae1ec3e2b7..4afb4733eb 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
@@ -42,7 +42,16 @@ module ActiveRecord
         # a record (as primary keys cannot be +nil+). This might be done via the
         # +SecureRandom.uuid+ method and a +before_save+ callback, for instance.
         def primary_key(name, type = :primary_key, **options)
-          options[:default] = options.fetch(:default, "gen_random_uuid()") if type == :uuid
+          if type == :uuid
+            options[:default] = options.fetch(:default, "gen_random_uuid()")
+          elsif options.delete(:auto_increment) == true && %i(integer bigint).include?(type)
+            type = if type == :bigint || options[:limit] == 8
+              :bigserial
+            else
+              :serial
+            end
+          end
+
           super
         end
 
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_dumper.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_dumper.rb
index c20baf655c..7808d37deb 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_dumper.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_dumper.rb
@@ -25,7 +25,7 @@ module ActiveRecord
         private
 
           def default_primary_key?(column)
-            schema_type(column) == :serial
+            schema_type(column) == :bigserial
           end
 
           def schema_type(column)
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/utils.rb b/activerecord/lib/active_record/connection_adapters/postgresql/utils.rb
index 1412928ca5..a3f9ce6d64 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/utils.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/utils.rb
@@ -35,6 +35,12 @@ module ActiveRecord
         end
 
         protected
+
+          def parts
+            @parts ||= [@schema, @identifier].compact
+          end
+
+        private
           def unquote(part)
             if part && part.start_with?('"')
               part[1..-2]
@@ -42,10 +48,6 @@ module ActiveRecord
               part
             end
           end
-
-          def parts
-            @parts ||= [@schema, @identifier].compact
-          end
       end
 
       module Utils # :nodoc:
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 28e80a084a..0ebd907cc0 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -70,7 +70,7 @@ module ActiveRecord
       ADAPTER_NAME = "PostgreSQL".freeze
 
       NATIVE_DATABASE_TYPES = {
-        primary_key: "serial primary key",
+        primary_key: "bigserial primary key",
         string:      { name: "character varying" },
         text:        { name: "text" },
         integer:     { name: "integer" },
@@ -404,10 +404,12 @@ module ActiveRecord
         @connection.server_version
       end
 
-      protected
+      private
 
         # See http://www.postgresql.org/docs/current/static/errcodes-appendix.html
         VALUE_LIMIT_VIOLATION = "22001"
+        NUMERIC_VALUE_OUT_OF_RANGE = "22003"
+        NOT_NULL_VIOLATION    = "23502"
         FOREIGN_KEY_VIOLATION = "23503"
         UNIQUE_VIOLATION      = "23505"
         SERIALIZATION_FAILURE = "40001"
@@ -423,6 +425,10 @@ module ActiveRecord
             InvalidForeignKey.new(message)
           when VALUE_LIMIT_VIOLATION
             ValueTooLong.new(message)
+          when NUMERIC_VALUE_OUT_OF_RANGE
+            RangeError.new(message)
+          when NOT_NULL_VIOLATION
+            NotNullViolation.new(message)
           when SERIALIZATION_FAILURE
             SerializationFailure.new(message)
           when DEADLOCK_DETECTED
@@ -432,9 +438,7 @@ module ActiveRecord
           end
         end
 
-      private
-
-        def get_oid_type(oid, fmod, column_name, sql_type = "") # :nodoc:
+        def get_oid_type(oid, fmod, column_name, sql_type = "")
           if !type_map.key?(oid)
             load_additional_types(type_map, [oid])
           end
@@ -447,7 +451,7 @@ module ActiveRecord
           }
         end
 
-        def initialize_type_map(m) # :nodoc:
+        def initialize_type_map(m)
           register_class_with_limit m, "int2", Type::Integer
           register_class_with_limit m, "int4", Type::Integer
           register_class_with_limit m, "int8", Type::Integer
@@ -515,7 +519,7 @@ module ActiveRecord
           load_additional_types(m)
         end
 
-        def extract_limit(sql_type) # :nodoc:
+        def extract_limit(sql_type)
           case sql_type
           when /^bigint/i, /^int8/i
             8
@@ -527,7 +531,7 @@ module ActiveRecord
         end
 
         # Extracts the value from a PostgreSQL column default definition.
-        def extract_value_from_default(default) # :nodoc:
+        def extract_value_from_default(default)
           case default
             # Quoted types
           when /\A[\(B]?'(.*)'.*::"?([\w. ]+)"?(?:\[\])?\z/m
@@ -553,15 +557,15 @@ module ActiveRecord
           end
         end
 
-        def extract_default_function(default_value, default) # :nodoc:
+        def extract_default_function(default_value, default)
           default if has_default_function?(default_value, default)
         end
 
-        def has_default_function?(default_value, default) # :nodoc:
+        def has_default_function?(default_value, default)
           !default_value && (%r{\w+\(.*\)|\(.*\)::\w+} === default)
         end
 
-        def load_additional_types(type_map, oids = nil) # :nodoc:
+        def load_additional_types(type_map, oids = nil)
           initializer = OID::TypeMapInitializer.new(type_map)
 
           if supports_ranges?
@@ -729,7 +733,7 @@ module ActiveRecord
         end
 
         # Returns the current ID of a table's sequence.
-        def last_insert_id_result(sequence_name) # :nodoc:
+        def last_insert_id_result(sequence_name)
           exec_query("SELECT currval('#{sequence_name}')", "SQL")
         end
 
@@ -751,7 +755,7 @@ module ActiveRecord
         # Query implementation notes:
         #  - format_type includes the column size constraint, e.g. varchar(50)
         #  - ::regclass is a function that gives the id for a table name
-        def column_definitions(table_name) # :nodoc:
+        def column_definitions(table_name)
           query(<<-end_sql, "SCHEMA")
               SELECT a.attname, format_type(a.atttypid, a.atttypmod),
                      pg_get_expr(d.adbin, d.adrelid), a.attnotnull, a.atttypid, a.atttypmod,
@@ -766,12 +770,12 @@ module ActiveRecord
           end_sql
         end
 
-        def extract_table_ref_from_insert_sql(sql) # :nodoc:
+        def extract_table_ref_from_insert_sql(sql)
           sql[/into\s("[A-Za-z0-9_."\[\]\s]+"|[A-Za-z0-9_."\[\]]+)\s*/im]
           $1.strip if $1
         end
 
-        def create_table_definition(*args) # :nodoc:
+        def create_table_definition(*args)
           PostgreSQL::TableDefinition.new(*args)
         end
 
diff --git a/activerecord/lib/active_record/connection_adapters/schema_cache.rb b/activerecord/lib/active_record/connection_adapters/schema_cache.rb
index 8219f132c3..3a319c4029 100644
--- a/activerecord/lib/active_record/connection_adapters/schema_cache.rb
+++ b/activerecord/lib/active_record/connection_adapters/schema_cache.rb
@@ -21,6 +21,22 @@ module ActiveRecord
         @data_sources = @data_sources.dup
       end
 
+      def encode_with(coder)
+        coder["columns"] = @columns
+        coder["columns_hash"] = @columns_hash
+        coder["primary_keys"] = @primary_keys
+        coder["data_sources"] = @data_sources
+        coder["version"] = ActiveRecord::Migrator.current_version
+      end
+
+      def init_with(coder)
+        @columns = coder["columns"]
+        @columns_hash = coder["columns_hash"]
+        @primary_keys = coder["primary_keys"]
+        @data_sources = coder["data_sources"]
+        @version = coder["version"]
+      end
+
       def primary_keys(table_name)
         @primary_keys[table_name] ||= data_source_exists?(table_name) ? connection.primary_key(table_name) : nil
       end
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/sqlite3/schema_definitions.rb
new file mode 100644
index 0000000000..d0b38dff4c
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3/schema_definitions.rb
@@ -0,0 +1,23 @@
+module ActiveRecord
+  module ConnectionAdapters
+    module SQLite3
+      module ColumnMethods
+        def primary_key(name, type = :primary_key, **options)
+          if options.delete(:auto_increment) == true && %i(integer bigint).include?(type)
+            type = :primary_key
+          end
+
+          super
+        end
+      end
+
+      class TableDefinition < ActiveRecord::ConnectionAdapters::TableDefinition
+        include ColumnMethods
+      end
+
+      class Table < ActiveRecord::ConnectionAdapters::Table
+        include ColumnMethods
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3/schema_dumper.rb b/activerecord/lib/active_record/connection_adapters/sqlite3/schema_dumper.rb
new file mode 100644
index 0000000000..c027fef83c
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3/schema_dumper.rb
@@ -0,0 +1,13 @@
+module ActiveRecord
+  module ConnectionAdapters
+    module SQLite3
+      module ColumnDumper
+        private
+
+          def default_primary_key?(column)
+            schema_type(column) == :integer
+          end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
index 0493ab4e4b..e761b9531a 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
@@ -3,6 +3,8 @@ require "active_record/connection_adapters/statement_pool"
 require "active_record/connection_adapters/sqlite3/explain_pretty_printer"
 require "active_record/connection_adapters/sqlite3/quoting"
 require "active_record/connection_adapters/sqlite3/schema_creation"
+require "active_record/connection_adapters/sqlite3/schema_definitions"
+require "active_record/connection_adapters/sqlite3/schema_dumper"
 
 gem "sqlite3", "~> 1.3.6"
 require "sqlite3"
@@ -52,6 +54,7 @@ module ActiveRecord
       ADAPTER_NAME = "SQLite".freeze
 
       include SQLite3::Quoting
+      include SQLite3::ColumnDumper
 
       NATIVE_DATABASE_TYPES = {
         primary_key:  "INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL",
@@ -75,6 +78,10 @@ module ActiveRecord
           end
       end
 
+      def update_table_definition(table_name, base) # :nodoc:
+        SQLite3::Table.new(table_name, base)
+      end
+
       def schema_creation # :nodoc:
         SQLite3::SchemaCreation.new self
       end
@@ -424,16 +431,16 @@ module ActiveRecord
         rename_column_indexes(table_name, column.name, new_column_name)
       end
 
-      protected
+      private
 
-        def table_structure(table_name) # :nodoc:
+        def table_structure(table_name)
           structure = exec_query("PRAGMA table_info(#{quote_table_name(table_name)})", "SCHEMA")
           raise(ActiveRecord::StatementInvalid, "Could not find table '#{table_name}'") if structure.empty?
           table_structure_with_collation(table_name, structure)
         end
         alias column_definitions table_structure
 
-        def alter_table(table_name, options = {}) #:nodoc:
+        def alter_table(table_name, options = {})
           altered_table_name = "a#{table_name}"
           caller = lambda { |definition| yield definition if block_given? }
 
@@ -444,12 +451,12 @@ module ActiveRecord
           end
         end
 
-        def move_table(from, to, options = {}, &block) #:nodoc:
+        def move_table(from, to, options = {}, &block)
           copy_table(from, to, options, &block)
           drop_table(from)
         end
 
-        def copy_table(from, to, options = {}) #:nodoc:
+        def copy_table(from, to, options = {})
           from_primary_key = primary_key(from)
           options[:id] = false
           create_table(to, options) do |definition|
@@ -475,7 +482,7 @@ module ActiveRecord
             options[:rename] || {})
         end
 
-        def copy_table_indexes(from, to, rename = {}) #:nodoc:
+        def copy_table_indexes(from, to, rename = {})
           indexes(from).each do |index|
             name = index.name
             if to == "a#{from}"
@@ -498,7 +505,7 @@ module ActiveRecord
           end
         end
 
-        def copy_table_contents(from, to, columns, rename = {}) #:nodoc:
+        def copy_table_contents(from, to, columns, rename = {})
           column_mappings = Hash[columns.map { |name| [name, name] }]
           rename.each { |a| column_mappings[a.last] = a.first }
           from_columns = columns(from).collect(&:name)
@@ -523,12 +530,13 @@ module ActiveRecord
           #   column *column_name* is not unique
           when /column(s)? .* (is|are) not unique/, /UNIQUE constraint failed: .*/
             RecordNotUnique.new(message)
+          when /.* may not be NULL/, /NOT NULL constraint failed: .*/
+            NotNullViolation.new(message)
           else
             super
           end
         end
 
-      private
         COLLATE_REGEX = /.*\"(\w+)\".*collate\s+\"(\w+)\".*/i.freeze
 
         def table_structure_with_collation(table_name, basic_structure)
@@ -569,6 +577,10 @@ module ActiveRecord
             basic_structure.to_hash
           end
         end
+
+        def create_table_definition(*args)
+          SQLite3::TableDefinition.new(*args)
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index 1fbe374ade..d4836faa4b 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -194,7 +194,7 @@ module ActiveRecord
                                    name, primary_key, id)
         end
         record
-      rescue RangeError
+      rescue ::RangeError
         raise RecordNotFound.new("Couldn't find #{name} with an out of range value for '#{primary_key}'",
                                  name, primary_key)
       end
@@ -223,7 +223,7 @@ module ActiveRecord
           statement.execute(hash.values, self, connection).first
         rescue TypeError
           raise ActiveRecord::StatementInvalid
-        rescue RangeError
+        rescue ::RangeError
           nil
         end
       end
@@ -299,14 +299,14 @@ module ActiveRecord
 
       private
 
-        def cached_find_by_statement(key, &block) # :nodoc:
+        def cached_find_by_statement(key, &block)
           cache = @find_by_statement_cache[connection.prepared_statements]
           cache[key] || cache.synchronize {
             cache[key] ||= StatementCache.create(connection, &block)
           }
         end
 
-        def relation # :nodoc:
+        def relation
           relation = Relation.create(self, arel_table, predicate_builder)
 
           if finder_needs_type_condition? && !ignore_default_scope?
@@ -316,7 +316,7 @@ module ActiveRecord
           end
         end
 
-        def table_metadata # :nodoc:
+        def table_metadata
           TableMetadata.new(self, arel_table)
         end
     end
diff --git a/activerecord/lib/active_record/enum.rb b/activerecord/lib/active_record/enum.rb
index 0a94ab58dd..0ab03b2ab3 100644
--- a/activerecord/lib/active_record/enum.rb
+++ b/activerecord/lib/active_record/enum.rb
@@ -140,6 +140,8 @@ module ActiveRecord
         end
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
       protected
 
         attr_reader :name, :mapping, :subtype
diff --git a/activerecord/lib/active_record/errors.rb b/activerecord/lib/active_record/errors.rb
index 6464d40c94..c812a05101 100644
--- a/activerecord/lib/active_record/errors.rb
+++ b/activerecord/lib/active_record/errors.rb
@@ -123,10 +123,46 @@ module ActiveRecord
   class InvalidForeignKey < WrappedDatabaseException
   end
 
+  # Raised when a foreign key constraint cannot be added because the column type does not match the referenced column type.
+  class MismatchedForeignKey < StatementInvalid
+    def initialize(adapter = nil, message: nil, table: nil, foreign_key: nil, target_table: nil, primary_key: nil)
+      @adapter = adapter
+      if table
+        msg = <<-EOM.strip_heredoc
+          Column `#{foreign_key}` on table `#{table}` has a type of `#{column_type(table, foreign_key)}`.
+          This does not match column `#{primary_key}` on `#{target_table}`, which has type `#{column_type(target_table, primary_key)}`.
+          To resolve this issue, change the type of the `#{foreign_key}` column on `#{table}` to be :integer. (For example `t.integer #{foreign_key}`).
+        EOM
+      else
+        msg = <<-EOM
+          There is a mismatch between the foreign key and primary key column types.
+          Verify that the foreign key column type and the primary key of the associated table match types.
+        EOM
+      end
+      if message
+        msg << "\nOriginal message: #{message}"
+      end
+      super(msg)
+    end
+
+    private
+      def column_type(table, column)
+        @adapter.columns(table).detect { |c| c.name == column }.sql_type
+      end
+  end
+
+  # Raised when a record cannot be inserted or updated because it would violate a not null constraint.
+  class NotNullViolation < StatementInvalid
+  end
+
   # Raised when a record cannot be inserted or updated because a value too long for a column type.
   class ValueTooLong < StatementInvalid
   end
 
+  # Raised when values that executed are out of range.
+  class RangeError < StatementInvalid
+  end
+
   # Raised when number of bind variables in statement given to +:condition+ key
   # (for example, when using {ActiveRecord::Base.find}[rdoc-ref:FinderMethods#find] method)
   # does not match number of expected values supplied.
diff --git a/activerecord/lib/active_record/fixture_set/file.rb b/activerecord/lib/active_record/fixture_set/file.rb
index 5ba354d758..6cf2e01179 100644
--- a/activerecord/lib/active_record/fixture_set/file.rb
+++ b/activerecord/lib/active_record/fixture_set/file.rb
@@ -66,10 +66,13 @@ module ActiveRecord
         # Validate our unmarshalled data.
         def validate(data)
           unless Hash === data || YAML::Omap === data
-            raise Fixture::FormatError, "fixture is not a hash"
+            raise Fixture::FormatError, "fixture is not a hash: #{@file}"
           end
 
-          raise Fixture::FormatError unless data.all? { |name, row| Hash === row }
+          invalid = data.reject { |_, row| Hash === row }
+          if invalid.any?
+            raise Fixture::FormatError, "fixture key is not a hash: #{@file}, keys: #{invalid.keys.inspect}"
+          end
           data
         end
     end
diff --git a/activerecord/lib/active_record/fixtures.rb b/activerecord/lib/active_record/fixtures.rb
index 21c5e5b5bb..3b4532a3f2 100644
--- a/activerecord/lib/active_record/fixtures.rb
+++ b/activerecord/lib/active_record/fixtures.rb
@@ -536,16 +536,16 @@ module ActiveRecord
           update_all_loaded_fixtures fixtures_map
 
           connection.transaction(requires_new: true) do
-            deleted_tables = Set.new
+            deleted_tables = Hash.new { |h, k| h[k] = Set.new }
             fixture_sets.each do |fs|
               conn = fs.model_class.respond_to?(:connection) ? fs.model_class.connection : connection
               table_rows = fs.table_rows
 
               table_rows.each_key do |table|
-                unless deleted_tables.include? table
+                unless deleted_tables[conn].include? table
                   conn.delete "DELETE FROM #{conn.quote_table_name(table)}", "Fixture Delete"
                 end
-                deleted_tables << table
+                deleted_tables[conn] << table
               end
 
               table_rows.each do |fixture_set_name, rows|
diff --git a/activerecord/lib/active_record/locking/optimistic.rb b/activerecord/lib/active_record/locking/optimistic.rb
index 82882469e3..2659c60f1f 100644
--- a/activerecord/lib/active_record/locking/optimistic.rb
+++ b/activerecord/lib/active_record/locking/optimistic.rb
@@ -69,7 +69,7 @@ module ActiveRecord
           send(lock_col + "=", previous_lock_value + 1)
         end
 
-        def _create_record(attribute_names = self.attribute_names, *) # :nodoc:
+        def _create_record(attribute_names = self.attribute_names, *)
           if locking_enabled?
             # We always want to persist the locking version, even if we don't detect
             # a change from the default, since the database might have no default
@@ -78,7 +78,7 @@ module ActiveRecord
           super
         end
 
-        def _update_record(attribute_names = self.attribute_names) #:nodoc:
+        def _update_record(attribute_names = self.attribute_names)
           return super unless locking_enabled?
 
           lock_col = self.class.locking_column
diff --git a/activerecord/lib/active_record/migration/compatibility.rb b/activerecord/lib/active_record/migration/compatibility.rb
index ae45ac7157..9c357e1604 100644
--- a/activerecord/lib/active_record/migration/compatibility.rb
+++ b/activerecord/lib/active_record/migration/compatibility.rb
@@ -104,11 +104,20 @@ module ActiveRecord
 
       class V5_0 < V5_1
         def create_table(table_name, options = {})
-          if ActiveRecord::Base.connection.adapter_name == "PostgreSQL"
+          if adapter_name == "PostgreSQL"
             if options[:id] == :uuid && !options[:default]
               options[:default] = "uuid_generate_v4()"
             end
           end
+
+          # Since 5.1 Postgres adapter uses bigserial type for primary
+          # keys by default and MySQL uses bigint. This compat layer makes old migrations utilize
+          # serial/int type instead -- the way it used to work before 5.1.
+          if options[:id].blank?
+            options[:id] = :integer
+            options[:auto_increment] = true
+          end
+
           super
         end
       end
diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index 8e13ee3564..60d8e95b21 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -181,7 +181,11 @@ module ActiveRecord
       _raise_readonly_record_error if readonly?
       destroy_associations
       self.class.connection.add_transaction_record(self)
-      destroy_row if persisted?
+      @_trigger_destroy_callback = if persisted?
+        destroy_row > 0
+      else
+        true
+      end
       @destroyed = true
       freeze
     end
@@ -519,6 +523,7 @@ module ActiveRecord
           raise ActiveRecord::StaleObjectError.new(self, "touch")
         end
 
+        @_trigger_update_callback = result
         result
       else
         true
@@ -550,10 +555,13 @@ module ActiveRecord
     def _update_record(attribute_names = self.attribute_names)
       attributes_values = arel_attributes_with_values_for_update(attribute_names)
       if attributes_values.empty?
-        0
+        rows_affected = 0
+        @_trigger_update_callback = true
       else
-        self.class.unscoped._update_record attributes_values, id, id_in_database
+        rows_affected = self.class.unscoped._update_record attributes_values, id, id_in_database
+        @_trigger_update_callback = rows_affected > 0
       end
+      rows_affected
     end
 
     # Creates a record with values matching those of the instance attributes
diff --git a/activerecord/lib/active_record/railtie.rb b/activerecord/lib/active_record/railtie.rb
index 7ce10df6d4..2701c5bca9 100644
--- a/activerecord/lib/active_record/railtie.rb
+++ b/activerecord/lib/active_record/railtie.rb
@@ -82,15 +82,15 @@ module ActiveRecord
       if config.active_record.delete(:use_schema_cache_dump)
         config.after_initialize do |app|
           ActiveSupport.on_load(:active_record) do
-            filename = File.join(app.config.paths["db"].first, "schema_cache.dump")
+            filename = File.join(app.config.paths["db"].first, "schema_cache.yml")
 
             if File.file?(filename)
-              cache = Marshal.load File.binread filename
+              cache = YAML.load(File.read(filename))
               if cache.version == ActiveRecord::Migrator.current_version
                 self.connection.schema_cache = cache
                 self.connection_pool.schema_cache = cache.dup
               else
-                warn "Ignoring db/schema_cache.dump because it has expired. The current schema version is #{ActiveRecord::Migrator.current_version}, but the one in the cache is #{cache.version}."
+                warn "Ignoring db/schema_cache.yml because it has expired. The current schema version is #{ActiveRecord::Migrator.current_version}, but the one in the cache is #{cache.version}."
               end
             end
           end
diff --git a/activerecord/lib/active_record/railties/controller_runtime.rb b/activerecord/lib/active_record/railties/controller_runtime.rb
index adb3c6c4e6..8658188623 100644
--- a/activerecord/lib/active_record/railties/controller_runtime.rb
+++ b/activerecord/lib/active_record/railties/controller_runtime.rb
@@ -6,10 +6,14 @@ module ActiveRecord
     module ControllerRuntime #:nodoc:
       extend ActiveSupport::Concern
 
+    # TODO Change this to private once we've dropped Ruby 2.2 support.
+    # Workaround for Ruby 2.2 "private attribute?" warning.
     protected
 
       attr_internal :db_runtime
 
+    private
+
       def process_action(action, *args)
         # We also need to reset the runtime before each action
         # because of queries in middleware or in cases we are streaming
diff --git a/activerecord/lib/active_record/railties/databases.rake b/activerecord/lib/active_record/railties/databases.rake
index 46235ab922..25d79a6c7d 100644
--- a/activerecord/lib/active_record/railties/databases.rake
+++ b/activerecord/lib/active_record/railties/databases.rake
@@ -265,19 +265,19 @@ db_namespace = namespace :db do
     end
 
     namespace :cache do
-      desc "Creates a db/schema_cache.dump file."
+      desc "Creates a db/schema_cache.yml file."
       task dump: [:environment, :load_config] do
-        con = ActiveRecord::Base.connection
-        filename = File.join(ActiveRecord::Tasks::DatabaseTasks.db_dir, "schema_cache.dump")
+        conn = ActiveRecord::Base.connection
+        filename = File.join(ActiveRecord::Tasks::DatabaseTasks.db_dir, "schema_cache.yml")
 
-        con.schema_cache.clear!
-        con.data_sources.each { |table| con.schema_cache.add(table) }
-        open(filename, "wb") { |f| f.write(Marshal.dump(con.schema_cache)) }
+        conn.schema_cache.clear!
+        conn.data_sources.each { |table| conn.schema_cache.add(table) }
+        open(filename, "wb") { |f| f.write(YAML.dump(conn.schema_cache)) }
       end
 
-      desc "Clears a db/schema_cache.dump file."
+      desc "Clears a db/schema_cache.yml file."
       task clear: [:environment, :load_config] do
-        filename = File.join(ActiveRecord::Tasks::DatabaseTasks.db_dir, "schema_cache.dump")
+        filename = File.join(ActiveRecord::Tasks::DatabaseTasks.db_dir, "schema_cache.yml")
         rm_f filename, verbose: false
       end
     end
diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index 17751c9571..e1a3c59f08 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -850,6 +850,10 @@ module ActiveRecord
         actual_source_reflection.options[:primary_key] || primary_key(klass || self.klass)
       end
 
+      def association_primary_key_type
+        klass.type_for_attribute(association_primary_key)
+      end
+
       # Gets an array of possible <tt>:through</tt> source reflection names in both singular and plural form.
       #
       #   class Post < ActiveRecord::Base
diff --git a/activerecord/lib/active_record/relation/delegation.rb b/activerecord/lib/active_record/relation/delegation.rb
index 4b9310b225..43dac0ed3d 100644
--- a/activerecord/lib/active_record/relation/delegation.rb
+++ b/activerecord/lib/active_record/relation/delegation.rb
@@ -78,7 +78,7 @@ module ActiveRecord
         end
       end
 
-      protected
+      private
 
         def method_missing(method, *args, &block)
           if @klass.respond_to?(method)
diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index 93c8722aa3..270511bede 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -76,7 +76,7 @@ module ActiveRecord
     #   Post.find_by "published_at < ?", 2.weeks.ago
     def find_by(arg, *args)
       where(arg, *args).take
-    rescue RangeError
+    rescue ::RangeError
       nil
     end
 
@@ -84,7 +84,7 @@ module ActiveRecord
     # an ActiveRecord::RecordNotFound error.
     def find_by!(arg, *args)
       where(arg, *args).take!
-    rescue RangeError
+    rescue ::RangeError
       raise RecordNotFound.new("Couldn't find #{@klass.name} with an out of range value",
                                @klass.name)
     end
@@ -333,7 +333,7 @@ module ActiveRecord
       end
 
       connection.select_value(relation, "#{name} Exists", relation.bound_attributes) ? true : false
-    rescue RangeError
+    rescue ::RangeError
       false
     end
 
@@ -439,143 +439,141 @@ module ActiveRecord
         reflections.none?(&:collection?)
       end
 
-    protected
+      private
 
-      def find_with_ids(*ids)
-        raise UnknownPrimaryKey.new(@klass) if primary_key.nil?
+        def find_with_ids(*ids)
+          raise UnknownPrimaryKey.new(@klass) if primary_key.nil?
 
-        expects_array = ids.first.kind_of?(Array)
-        return ids.first if expects_array && ids.first.empty?
+          expects_array = ids.first.kind_of?(Array)
+          return ids.first if expects_array && ids.first.empty?
 
-        ids = ids.flatten.compact.uniq
+          ids = ids.flatten.compact.uniq
 
-        case ids.size
-        when 0
-          raise RecordNotFound, "Couldn't find #{@klass.name} without an ID"
-        when 1
-          result = find_one(ids.first)
-          expects_array ? [ result ] : result
-        else
-          find_some(ids)
+          case ids.size
+          when 0
+            raise RecordNotFound, "Couldn't find #{@klass.name} without an ID"
+          when 1
+            result = find_one(ids.first)
+            expects_array ? [ result ] : result
+          else
+            find_some(ids)
+          end
+        rescue ::RangeError
+          raise RecordNotFound, "Couldn't find #{@klass.name} with an out of range ID"
         end
-      rescue RangeError
-        raise RecordNotFound, "Couldn't find #{@klass.name} with an out of range ID"
-      end
 
-      def find_one(id)
-        if ActiveRecord::Base === id
-          id = id.id
-          ActiveSupport::Deprecation.warn(<<-MSG.squish)
+        def find_one(id)
+          if ActiveRecord::Base === id
+            id = id.id
+            ActiveSupport::Deprecation.warn(<<-MSG.squish)
             You are passing an instance of ActiveRecord::Base to `find`.
             Please pass the id of the object by calling `.id`.
           MSG
-        end
+          end
 
-        relation = where(primary_key => id)
-        record = relation.take
+          relation = where(primary_key => id)
+          record = relation.take
 
-        raise_record_not_found_exception!(id, 0, 1) unless record
+          raise_record_not_found_exception!(id, 0, 1) unless record
 
-        record
-      end
+          record
+        end
 
-      def find_some(ids)
-        return find_some_ordered(ids) unless order_values.present?
+        def find_some(ids)
+          return find_some_ordered(ids) unless order_values.present?
 
-        result = where(primary_key => ids).to_a
+          result = where(primary_key => ids).to_a
 
-        expected_size =
-          if limit_value && ids.size > limit_value
-            limit_value
-          else
-            ids.size
-          end
+          expected_size =
+            if limit_value && ids.size > limit_value
+              limit_value
+            else
+              ids.size
+            end
 
-        # 11 ids with limit 3, offset 9 should give 2 results.
-        if offset_value && (ids.size - offset_value < expected_size)
-          expected_size = ids.size - offset_value
-        end
+          # 11 ids with limit 3, offset 9 should give 2 results.
+          if offset_value && (ids.size - offset_value < expected_size)
+            expected_size = ids.size - offset_value
+          end
 
-        if result.size == expected_size
-          result
-        else
-          raise_record_not_found_exception!(ids, result.size, expected_size)
+          if result.size == expected_size
+            result
+          else
+            raise_record_not_found_exception!(ids, result.size, expected_size)
+          end
         end
-      end
 
-      def find_some_ordered(ids)
-        ids = ids.slice(offset_value || 0, limit_value || ids.size) || []
+        def find_some_ordered(ids)
+          ids = ids.slice(offset_value || 0, limit_value || ids.size) || []
 
-        result = except(:limit, :offset).where(primary_key => ids).records
+          result = except(:limit, :offset).where(primary_key => ids).records
 
-        if result.size == ids.size
-          pk_type = @klass.type_for_attribute(primary_key)
+          if result.size == ids.size
+            pk_type = @klass.type_for_attribute(primary_key)
 
-          records_by_id = result.index_by(&:id)
-          ids.map { |id| records_by_id.fetch(pk_type.cast(id)) }
-        else
-          raise_record_not_found_exception!(ids, result.size, ids.size)
+            records_by_id = result.index_by(&:id)
+            ids.map { |id| records_by_id.fetch(pk_type.cast(id)) }
+          else
+            raise_record_not_found_exception!(ids, result.size, ids.size)
+          end
         end
-      end
 
-      def find_take
-        if loaded?
-          records.first
-        else
-          @take ||= limit(1).records.first
+        def find_take
+          if loaded?
+            records.first
+          else
+            @take ||= limit(1).records.first
+          end
         end
-      end
 
-      def find_take_with_limit(limit)
-        if loaded?
-          records.take(limit)
-        else
-          limit(limit).to_a
+        def find_take_with_limit(limit)
+          if loaded?
+            records.take(limit)
+          else
+            limit(limit).to_a
+          end
         end
-      end
 
-      def find_nth(index)
-        @offsets[offset_index + index] ||= find_nth_with_limit(index, 1).first
-      end
+        def find_nth(index)
+          @offsets[offset_index + index] ||= find_nth_with_limit(index, 1).first
+        end
 
-      def find_nth_with_limit(index, limit)
-        if loaded?
-          records[index, limit] || []
-        else
-          relation = if order_values.empty? && primary_key
-            order(arel_attribute(primary_key).asc)
+        def find_nth_with_limit(index, limit)
+          if loaded?
+            records[index, limit] || []
           else
-            self
+            relation = if order_values.empty? && primary_key
+              order(arel_attribute(primary_key).asc)
+            else
+              self
+            end
+
+            relation = relation.offset(offset_index + index) unless index.zero?
+            relation.limit(limit).to_a
           end
-
-          relation = relation.offset(offset_index + index) unless index.zero?
-          relation.limit(limit).to_a
         end
-      end
 
-      def find_nth_from_last(index)
-        if loaded?
-          records[-index]
-        else
-          relation = if order_values.empty? && primary_key
-            order(arel_attribute(primary_key).asc)
+        def find_nth_from_last(index)
+          if loaded?
+            records[-index]
           else
-            self
+            relation = if order_values.empty? && primary_key
+              order(arel_attribute(primary_key).asc)
+            else
+              self
+            end
+
+            relation.to_a[-index]
+            # TODO: can be made more performant on large result sets by
+            # for instance, last(index)[-index] (which would require
+            # refactoring the last(n) finder method to make test suite pass),
+            # or by using a combination of reverse_order, limit, and offset,
+            # e.g., reverse_order.offset(index-1).first
           end
-
-          relation.to_a[-index]
-          # TODO: can be made more performant on large result sets by
-          # for instance, last(index)[-index] (which would require
-          # refactoring the last(n) finder method to make test suite pass),
-          # or by using a combination of reverse_order, limit, and offset,
-          # e.g., reverse_order.offset(index-1).first
         end
-      end
-
-    private
 
-      def find_last(limit)
-        limit ? records.last(limit) : records.last
-      end
+        def find_last(limit)
+          limit ? records.last(limit) : records.last
+        end
   end
 end
diff --git a/activerecord/lib/active_record/relation/predicate_builder.rb b/activerecord/lib/active_record/relation/predicate_builder.rb
index 780a1ee422..f9f6ff403e 100644
--- a/activerecord/lib/active_record/relation/predicate_builder.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder.rb
@@ -66,6 +66,8 @@ module ActiveRecord
       handler_for(value).call(attribute, value)
     end
 
+    # TODO Change this to private once we've dropped Ruby 2.2 support.
+    # Workaround for Ruby 2.2 "private attribute?" warning.
     protected
 
       attr_reader :table
diff --git a/activerecord/lib/active_record/relation/predicate_builder/array_handler.rb b/activerecord/lib/active_record/relation/predicate_builder/array_handler.rb
index 6400caba06..88b6c37d43 100644
--- a/activerecord/lib/active_record/relation/predicate_builder/array_handler.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder/array_handler.rb
@@ -29,6 +29,8 @@ module ActiveRecord
         array_predicates.inject { |composite, predicate| composite.or(predicate) }
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
       protected
 
         attr_reader :predicate_builder
diff --git a/activerecord/lib/active_record/relation/predicate_builder/association_query_handler.rb b/activerecord/lib/active_record/relation/predicate_builder/association_query_handler.rb
index 7e20cb2c63..29860ec677 100644
--- a/activerecord/lib/active_record/relation/predicate_builder/association_query_handler.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder/association_query_handler.rb
@@ -28,6 +28,8 @@ module ActiveRecord
         predicate_builder.build_from_hash(queries)
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
       protected
 
         attr_reader :predicate_builder
@@ -68,9 +70,6 @@ module ActiveRecord
           case value
           when Relation
             value.klass.base_class
-          when Array
-            val = value.compact.first
-            val.class.base_class if val.is_a?(Base)
           when Base
             value.class.base_class
           end
diff --git a/activerecord/lib/active_record/relation/predicate_builder/base_handler.rb b/activerecord/lib/active_record/relation/predicate_builder/base_handler.rb
index 65c5159704..3bb1037885 100644
--- a/activerecord/lib/active_record/relation/predicate_builder/base_handler.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder/base_handler.rb
@@ -9,6 +9,8 @@ module ActiveRecord
         predicate_builder.build(attribute, value.id)
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
       protected
 
         attr_reader :predicate_builder
diff --git a/activerecord/lib/active_record/relation/predicate_builder/class_handler.rb b/activerecord/lib/active_record/relation/predicate_builder/class_handler.rb
index 0a6574fcf1..810937ead6 100644
--- a/activerecord/lib/active_record/relation/predicate_builder/class_handler.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder/class_handler.rb
@@ -10,6 +10,8 @@ module ActiveRecord
         predicate_builder.build(attribute, value.name)
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
       protected
 
         attr_reader :predicate_builder
diff --git a/activerecord/lib/active_record/relation/predicate_builder/polymorphic_array_handler.rb b/activerecord/lib/active_record/relation/predicate_builder/polymorphic_array_handler.rb
index 0c7f92b3d0..335124c952 100644
--- a/activerecord/lib/active_record/relation/predicate_builder/polymorphic_array_handler.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder/polymorphic_array_handler.rb
@@ -21,6 +21,8 @@ module ActiveRecord
         end
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
       protected
 
         attr_reader :predicate_builder
diff --git a/activerecord/lib/active_record/relation/spawn_methods.rb b/activerecord/lib/active_record/relation/spawn_methods.rb
index 190e339ea8..ada89b5ec3 100644
--- a/activerecord/lib/active_record/relation/spawn_methods.rb
+++ b/activerecord/lib/active_record/relation/spawn_methods.rb
@@ -66,7 +66,7 @@ module ActiveRecord
 
     private
 
-      def relation_with(values) # :nodoc:
+      def relation_with(values)
         result = Relation.create(klass, table, predicate_builder, values)
         result.extend(*extending_values) if extending_values.any?
         result
diff --git a/activerecord/lib/active_record/relation/where_clause.rb b/activerecord/lib/active_record/relation/where_clause.rb
index 402f8acfd1..ef0d059d1c 100644
--- a/activerecord/lib/active_record/relation/where_clause.rb
+++ b/activerecord/lib/active_record/relation/where_clause.rb
@@ -84,6 +84,8 @@ module ActiveRecord
         @empty ||= new([], [])
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
       protected
 
         attr_reader :predicates
diff --git a/activerecord/lib/active_record/relation/where_clause_factory.rb b/activerecord/lib/active_record/relation/where_clause_factory.rb
index 1e7deeffad..737bc278bd 100644
--- a/activerecord/lib/active_record/relation/where_clause_factory.rb
+++ b/activerecord/lib/active_record/relation/where_clause_factory.rb
@@ -27,6 +27,8 @@ module ActiveRecord
         WhereClause.new(parts, binds || [])
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
       protected
 
         attr_reader :klass, :predicate_builder
diff --git a/activerecord/lib/active_record/sanitization.rb b/activerecord/lib/active_record/sanitization.rb
index 3d52dc44cf..647834b12e 100644
--- a/activerecord/lib/active_record/sanitization.rb
+++ b/activerecord/lib/active_record/sanitization.rb
@@ -4,7 +4,7 @@ module ActiveRecord
     extend ActiveSupport::Concern
 
     module ClassMethods
-      protected
+      private
 
         # Accepts an array or string of SQL conditions and sanitizes
         # them into a valid SQL fragment for a WHERE clause.
@@ -20,7 +20,7 @@ module ActiveRecord
         #
         #   sanitize_sql_for_conditions("name='foo''bar' and group_id='4'")
         #   # => "name='foo''bar' and group_id='4'"
-        def sanitize_sql_for_conditions(condition)
+        def sanitize_sql_for_conditions(condition) # :doc:
           return nil if condition.blank?
 
           case condition
@@ -46,7 +46,7 @@ module ActiveRecord
         #
         #   sanitize_sql_for_assignment("name=NULL and group_id='4'")
         #   # => "name=NULL and group_id='4'"
-        def sanitize_sql_for_assignment(assignments, default_table_name = self.table_name)
+        def sanitize_sql_for_assignment(assignments, default_table_name = self.table_name) # :doc:
           case assignments
           when Array; sanitize_sql_array(assignments)
           when Hash;  sanitize_sql_hash_for_assignment(assignments, default_table_name)
@@ -62,7 +62,7 @@ module ActiveRecord
         #
         #   sanitize_sql_for_order("id ASC")
         #   # => "id ASC"
-        def sanitize_sql_for_order(condition)
+        def sanitize_sql_for_order(condition) # :doc:
           if condition.is_a?(Array) && condition.first.to_s.include?("?")
             sanitize_sql_array(condition)
           else
@@ -85,7 +85,7 @@ module ActiveRecord
         #
         #   { address: Address.new("813 abc st.", "chicago") }
         #   # => { address_street: "813 abc st.", address_city: "chicago" }
-        def expand_hash_conditions_for_aggregates(attrs)
+        def expand_hash_conditions_for_aggregates(attrs) # :doc:
           expanded_attrs = {}
           attrs.each do |attr, value|
             if aggregation = reflect_on_aggregation(attr.to_sym)
@@ -108,7 +108,7 @@ module ActiveRecord
         #
         #   sanitize_sql_hash_for_assignment({ status: nil, group_id: 1 }, "posts")
         #   # => "`posts`.`status` = NULL, `posts`.`group_id` = 1"
-        def sanitize_sql_hash_for_assignment(attrs, table)
+        def sanitize_sql_hash_for_assignment(attrs, table) # :doc:
           c = connection
           attrs.map do |attr, value|
             value = type_for_attribute(attr.to_s).serialize(value)
@@ -130,7 +130,7 @@ module ActiveRecord
         #
         #   sanitize_sql_like("snake_cased_string", "!")
         #   # => "snake!_cased!_string"
-        def sanitize_sql_like(string, escape_character = "\\")
+        def sanitize_sql_like(string, escape_character = "\\") # :doc:
           pattern = Regexp.union(escape_character, "%", "_")
           string.gsub(pattern) { |x| [escape_character, x].join }
         end
@@ -146,7 +146,7 @@ module ActiveRecord
         #
         #   sanitize_sql_array(["name='%s' and group_id='%s'", "foo'bar", 4])
         #   # => "name='foo''bar' and group_id='4'"
-        def sanitize_sql_array(ary)
+        def sanitize_sql_array(ary) # :doc:
           statement, *values = ary
           if values.first.is_a?(Hash) && /:\w+/.match?(statement)
             replace_named_bind_variables(statement, values.first)
@@ -159,7 +159,7 @@ module ActiveRecord
           end
         end
 
-        def replace_bind_variables(statement, values) # :nodoc:
+        def replace_bind_variables(statement, values)
           raise_if_bind_arity_mismatch(statement, statement.count("?"), values.size)
           bound = values.dup
           c = connection
@@ -168,7 +168,7 @@ module ActiveRecord
           end
         end
 
-        def replace_bind_variable(value, c = connection) # :nodoc:
+        def replace_bind_variable(value, c = connection)
           if ActiveRecord::Relation === value
             value.to_sql
           else
@@ -176,7 +176,7 @@ module ActiveRecord
           end
         end
 
-        def replace_named_bind_variables(statement, bind_vars) # :nodoc:
+        def replace_named_bind_variables(statement, bind_vars)
           statement.gsub(/(:?):([a-zA-Z]\w*)/) do |match|
             if $1 == ":" # skip postgresql casts
               match # return the whole match
@@ -188,7 +188,7 @@ module ActiveRecord
           end
         end
 
-        def quote_bound_value(value, c = connection) # :nodoc:
+        def quote_bound_value(value, c = connection)
           if value.respond_to?(:map) && !value.acts_like?(:string)
             if value.respond_to?(:empty?) && value.empty?
               c.quote(nil)
@@ -200,7 +200,7 @@ module ActiveRecord
           end
         end
 
-        def raise_if_bind_arity_mismatch(statement, expected, provided) # :nodoc:
+        def raise_if_bind_arity_mismatch(statement, expected, provided)
           unless expected == provided
             raise PreparedStatementInvalid, "wrong number of bind variables (#{provided} for #{expected}) in: #{statement}"
           end
diff --git a/activerecord/lib/active_record/schema.rb b/activerecord/lib/active_record/schema.rb
index 99e54a8b24..7a2bc9c8af 100644
--- a/activerecord/lib/active_record/schema.rb
+++ b/activerecord/lib/active_record/schema.rb
@@ -61,7 +61,7 @@ module ActiveRecord
       #
       #   ActiveRecord::Schema.new.migrations_paths
       #   # => ["db/migrate"] # Rails migration path by default.
-      def migrations_paths # :nodoc:
+      def migrations_paths
         ActiveRecord::Migrator.migrations_paths
       end
   end
diff --git a/activerecord/lib/active_record/scoping/default.rb b/activerecord/lib/active_record/scoping/default.rb
index 9d8253faa3..2daa48859a 100644
--- a/activerecord/lib/active_record/scoping/default.rb
+++ b/activerecord/lib/active_record/scoping/default.rb
@@ -44,7 +44,7 @@ module ActiveRecord
           self.current_scope = nil
         end
 
-        protected
+        private
 
           # Use this macro in your model to set a default scope for all operations on
           # the model.
@@ -87,7 +87,7 @@ module ActiveRecord
           #       # Should return a scope, you can call 'super' here etc.
           #     end
           #   end
-          def default_scope(scope = nil)
+          def default_scope(scope = nil) # :doc:
             scope = Proc.new if block_given?
 
             if scope.is_a?(Relation) || !scope.respond_to?(:call)
@@ -101,7 +101,7 @@ module ActiveRecord
             self.default_scopes += [scope]
           end
 
-          def build_default_scope(base_rel = nil) # :nodoc:
+          def build_default_scope(base_rel = nil)
             return if abstract_class?
 
             if default_scope_override.nil?
@@ -122,18 +122,18 @@ module ActiveRecord
             end
           end
 
-          def ignore_default_scope? # :nodoc:
+          def ignore_default_scope?
             ScopeRegistry.value_for(:ignore_default_scope, base_class)
           end
 
-          def ignore_default_scope=(ignore) # :nodoc:
+          def ignore_default_scope=(ignore)
             ScopeRegistry.set_value_for(:ignore_default_scope, base_class, ignore)
           end
 
           # The ignore_default_scope flag is used to prevent an infinite recursion
           # situation where a default scope references a scope which has a default
           # scope which references a scope...
-          def evaluate_default_scope # :nodoc:
+          def evaluate_default_scope
             return if ignore_default_scope?
 
             begin
diff --git a/activerecord/lib/active_record/scoping/named.rb b/activerecord/lib/active_record/scoping/named.rb
index 6af84c1266..27cdf8cb7e 100644
--- a/activerecord/lib/active_record/scoping/named.rb
+++ b/activerecord/lib/active_record/scoping/named.rb
@@ -171,14 +171,14 @@ module ActiveRecord
           end
         end
 
-      protected
+        private
 
-        def valid_scope_name?(name)
-          if respond_to?(name, true) && logger
-            logger.warn "Creating scope :#{name}. " \
-                        "Overwriting existing method #{self.name}.#{name}."
+          def valid_scope_name?(name)
+            if respond_to?(name, true) && logger
+              logger.warn "Creating scope :#{name}. " \
+                "Overwriting existing method #{self.name}.#{name}."
+            end
           end
-        end
       end
     end
   end
diff --git a/activerecord/lib/active_record/store.rb b/activerecord/lib/active_record/store.rb
index 066573192e..d4be20d999 100644
--- a/activerecord/lib/active_record/store.rb
+++ b/activerecord/lib/active_record/store.rb
@@ -121,18 +121,17 @@ module ActiveRecord
       end
     end
 
-    protected
-      def read_store_attribute(store_attribute, key)
+    private
+      def read_store_attribute(store_attribute, key) # :doc:
         accessor = store_accessor_for(store_attribute)
         accessor.read(self, store_attribute, key)
       end
 
-      def write_store_attribute(store_attribute, key, value)
+      def write_store_attribute(store_attribute, key, value) # :doc:
         accessor = store_accessor_for(store_attribute)
         accessor.write(self, store_attribute, key, value)
       end
 
-    private
       def store_accessor_for(store_attribute)
         type_for_attribute(store_attribute.to_s).accessor
       end
diff --git a/activerecord/lib/active_record/table_metadata.rb b/activerecord/lib/active_record/table_metadata.rb
index 58184f3872..b618e5cfcd 100644
--- a/activerecord/lib/active_record/table_metadata.rb
+++ b/activerecord/lib/active_record/table_metadata.rb
@@ -64,6 +64,8 @@ module ActiveRecord
       association && association.polymorphic?
     end
 
+    # TODO Change this to private once we've dropped Ruby 2.2 support.
+    # Workaround for Ruby 2.2 "private attribute?" warning.
     protected
 
       attr_reader :klass, :arel_table, :association
diff --git a/activerecord/lib/active_record/transactions.rb b/activerecord/lib/active_record/transactions.rb
index af3fc88282..f22acd0f77 100644
--- a/activerecord/lib/active_record/transactions.rb
+++ b/activerecord/lib/active_record/transactions.rb
@@ -407,10 +407,10 @@ module ActiveRecord
       end
     end
 
-    protected
+    private
 
       # Save the new record state and id of a record so it can be restored later if a transaction fails.
-      def remember_transaction_record_state #:nodoc:
+      def remember_transaction_record_state
         @_start_transaction_state[:id] = id
         @_start_transaction_state.reverse_merge!(
           new_record: @new_record,
@@ -421,18 +421,18 @@ module ActiveRecord
       end
 
       # Clear the new record state and id of a record.
-      def clear_transaction_record_state #:nodoc:
+      def clear_transaction_record_state
         @_start_transaction_state[:level] = (@_start_transaction_state[:level] || 0) - 1
         force_clear_transaction_record_state if @_start_transaction_state[:level] < 1
       end
 
       # Force to clear the transaction record state.
-      def force_clear_transaction_record_state #:nodoc:
+      def force_clear_transaction_record_state
         @_start_transaction_state.clear
       end
 
       # Restore the new record state and id of a record that was previously saved by a call to save_record_state.
-      def restore_transaction_record_state(force = false) #:nodoc:
+      def restore_transaction_record_state(force = false)
         unless @_start_transaction_state.empty?
           transaction_level = (@_start_transaction_state[:level] || 0) - 1
           if transaction_level < 1 || force
@@ -450,31 +450,30 @@ module ActiveRecord
       end
 
       # Determine if a record was created or destroyed in a transaction. State should be one of :new_record or :destroyed.
-      def transaction_record_state(state) #:nodoc:
+      def transaction_record_state(state)
         @_start_transaction_state[state]
       end
 
       # Determine if a transaction included an action for :create, :update, or :destroy. Used in filtering callbacks.
-      def transaction_include_any_action?(actions) #:nodoc:
+      def transaction_include_any_action?(actions)
         actions.any? do |action|
           case action
           when :create
             transaction_record_state(:new_record)
           when :destroy
-            destroyed?
+            defined?(@_trigger_destroy_callback) && @_trigger_destroy_callback
           when :update
-            !(transaction_record_state(:new_record) || destroyed?)
+            !(transaction_record_state(:new_record) || destroyed?) &&
+              (defined?(@_trigger_update_callback) && @_trigger_update_callback)
           end
         end
       end
 
-    private
-
-      def set_transaction_state(state) # :nodoc:
+      def set_transaction_state(state)
         @transaction_state = state
       end
 
-      def has_transactional_callbacks? # :nodoc:
+      def has_transactional_callbacks?
         !_rollback_callbacks.empty? || !_commit_callbacks.empty? || !_before_commit_callbacks.empty?
       end
 
diff --git a/activerecord/lib/active_record/type.rb b/activerecord/lib/active_record/type.rb
index 0b48d2186a..4f632660a8 100644
--- a/activerecord/lib/active_record/type.rb
+++ b/activerecord/lib/active_record/type.rb
@@ -5,7 +5,10 @@ require "active_record/type/internal/timezone"
 
 require "active_record/type/date"
 require "active_record/type/date_time"
+require "active_record/type/decimal_without_scale"
 require "active_record/type/time"
+require "active_record/type/text"
+require "active_record/type/unsigned_integer"
 
 require "active_record/type/serialized"
 require "active_record/type/adapter_specific_registry"
@@ -53,12 +56,9 @@ module ActiveRecord
     Binary = ActiveModel::Type::Binary
     Boolean = ActiveModel::Type::Boolean
     Decimal = ActiveModel::Type::Decimal
-    DecimalWithoutScale = ActiveModel::Type::DecimalWithoutScale
     Float = ActiveModel::Type::Float
     Integer = ActiveModel::Type::Integer
     String = ActiveModel::Type::String
-    Text = ActiveModel::Type::Text
-    UnsignedInteger = ActiveModel::Type::UnsignedInteger
     Value = ActiveModel::Type::Value
 
     register(:big_integer, Type::BigInteger, override: false)
diff --git a/activerecord/lib/active_record/type/adapter_specific_registry.rb b/activerecord/lib/active_record/type/adapter_specific_registry.rb
index d0f9581576..7cc866f7a7 100644
--- a/activerecord/lib/active_record/type/adapter_specific_registry.rb
+++ b/activerecord/lib/active_record/type/adapter_specific_registry.rb
@@ -50,6 +50,8 @@ module ActiveRecord
         priority <=> other.priority
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
       protected
 
         attr_reader :name, :block, :adapter, :override
@@ -110,6 +112,8 @@ module ActiveRecord
         super | 4
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
       protected
 
         attr_reader :options, :klass
diff --git a/activerecord/lib/active_record/type/decimal_without_scale.rb b/activerecord/lib/active_record/type/decimal_without_scale.rb
new file mode 100644
index 0000000000..7ce33e9cd3
--- /dev/null
+++ b/activerecord/lib/active_record/type/decimal_without_scale.rb
@@ -0,0 +1,9 @@
+module ActiveRecord
+  module Type
+    class DecimalWithoutScale < ActiveModel::Type::BigInteger # :nodoc:
+      def type
+        :decimal
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/type/text.rb b/activerecord/lib/active_record/type/text.rb
new file mode 100644
index 0000000000..cb1949700a
--- /dev/null
+++ b/activerecord/lib/active_record/type/text.rb
@@ -0,0 +1,9 @@
+module ActiveRecord
+  module Type
+    class Text < ActiveModel::Type::String # :nodoc:
+      def type
+        :text
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/type/unsigned_integer.rb b/activerecord/lib/active_record/type/unsigned_integer.rb
new file mode 100644
index 0000000000..9ae0109f9f
--- /dev/null
+++ b/activerecord/lib/active_record/type/unsigned_integer.rb
@@ -0,0 +1,15 @@
+module ActiveRecord
+  module Type
+    class UnsignedInteger < ActiveModel::Type::Integer # :nodoc:
+      private
+
+        def max_value
+          super * 2
+        end
+
+        def min_value
+          0
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/type_caster/connection.rb b/activerecord/lib/active_record/type_caster/connection.rb
index 6c54792e26..9f7bbe8843 100644
--- a/activerecord/lib/active_record/type_caster/connection.rb
+++ b/activerecord/lib/active_record/type_caster/connection.rb
@@ -12,6 +12,8 @@ module ActiveRecord
         connection.type_cast_from_column(column, value)
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
       protected
 
         attr_reader :table_name
diff --git a/activerecord/lib/active_record/type_caster/map.rb b/activerecord/lib/active_record/type_caster/map.rb
index 52529a6b42..9f79723125 100644
--- a/activerecord/lib/active_record/type_caster/map.rb
+++ b/activerecord/lib/active_record/type_caster/map.rb
@@ -11,6 +11,8 @@ module ActiveRecord
         type.serialize(value)
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
       protected
 
         attr_reader :types
diff --git a/activerecord/lib/active_record/validations.rb b/activerecord/lib/active_record/validations.rb
index c013a4518f..9633f226f0 100644
--- a/activerecord/lib/active_record/validations.rb
+++ b/activerecord/lib/active_record/validations.rb
@@ -68,7 +68,7 @@ module ActiveRecord
 
     alias_method :validate, :valid?
 
-  protected
+  private
 
     def default_validation_context
       new_record? ? :create : :update
@@ -78,7 +78,7 @@ module ActiveRecord
       raise(RecordInvalid.new(self))
     end
 
-    def perform_validations(options = {}) # :nodoc:
+    def perform_validations(options = {})
       options[:validate] == false || valid?(options[:context])
     end
   end
diff --git a/activerecord/lib/active_record/validations/uniqueness.rb b/activerecord/lib/active_record/validations/uniqueness.rb
index 512fdadacc..9e8edfbfaf 100644
--- a/activerecord/lib/active_record/validations/uniqueness.rb
+++ b/activerecord/lib/active_record/validations/uniqueness.rb
@@ -33,13 +33,13 @@ module ActiveRecord
         end
       end
 
-    protected
+    private
       # The check for an existing value should be run from a class that
       # isn't abstract. This means working down from the current class
       # (self), to the first non-abstract class. Since classes don't know
       # their subclasses, we have to build the hierarchy between self and
       # the record's class.
-      def find_finder_class_for(record) #:nodoc:
+      def find_finder_class_for(record)
         class_hierarchy = [record.class]
 
         while class_hierarchy.first != @klass
@@ -49,7 +49,7 @@ module ActiveRecord
         class_hierarchy.detect { |klass| !klass.abstract_class? }
       end
 
-      def build_relation(klass, attribute, value) # :nodoc:
+      def build_relation(klass, attribute, value)
         if reflection = klass._reflect_on_association(attribute)
           attribute = reflection.foreign_key
           value = value.attributes[reflection.klass.primary_key] unless value.nil?
diff --git a/activerecord/lib/rails/generators/active_record/migration/migration_generator.rb b/activerecord/lib/rails/generators/active_record/migration/migration_generator.rb
index 12d1f58f67..8511531af7 100644
--- a/activerecord/lib/rails/generators/active_record/migration/migration_generator.rb
+++ b/activerecord/lib/rails/generators/active_record/migration/migration_generator.rb
@@ -13,9 +13,13 @@ module ActiveRecord
         migration_template @migration_template, "db/migrate/#{file_name}.rb"
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
       protected
         attr_reader :migration_action, :join_tables
 
+      private
+
         # Sets the default migration template that is being used for the generation of the migration.
         # Depending on command line arguments, the migration template and the table name instance
         # variables are set up.
@@ -52,7 +56,6 @@ module ActiveRecord
           end.to_sym
         end
 
-      private
         def attributes_with_index
           attributes.select { |a| !a.reference? && a.has_index? }
         end
diff --git a/activerecord/lib/rails/generators/active_record/model/model_generator.rb b/activerecord/lib/rails/generators/active_record/model/model_generator.rb
index f1ddc61688..61a8d3c100 100644
--- a/activerecord/lib/rails/generators/active_record/model/model_generator.rb
+++ b/activerecord/lib/rails/generators/active_record/model/model_generator.rb
@@ -33,7 +33,7 @@ module ActiveRecord
 
       hook_for :test_framework
 
-      protected
+      private
 
         def attributes_with_index
           attributes.select { |a| !a.reference? && a.has_index? }
diff --git a/activerecord/test/assets/schema_dump_5_1.yml b/activerecord/test/assets/schema_dump_5_1.yml
new file mode 100644
index 0000000000..f37977daf2
--- /dev/null
+++ b/activerecord/test/assets/schema_dump_5_1.yml
@@ -0,0 +1,345 @@
+--- !ruby/object:ActiveRecord::ConnectionAdapters::SchemaCache
+columns:
+  posts:
+  - &1 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: id
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: INTEGER
+      type: :integer
+      limit: 
+      precision: 
+      scale: 
+    'null': false
+    default: 
+    default_function: 
+    collation: 
+    comment: 
+  - &2 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: author_id
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: integer
+      type: :integer
+      limit: 
+      precision: 
+      scale: 
+    'null': true
+    default: 
+    default_function: 
+    collation: 
+    comment: 
+  - &3 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: title
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: varchar
+      type: :string
+      limit: 
+      precision: 
+      scale: 
+    'null': false
+    default: 
+    default_function: 
+    collation: 
+    comment: 
+  - &4 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: body
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: text
+      type: :text
+      limit: 
+      precision: 
+      scale: 
+    'null': false
+    default: 
+    default_function: 
+    collation: 
+    comment: 
+  - &5 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: type
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: varchar
+      type: :string
+      limit: 
+      precision: 
+      scale: 
+    'null': true
+    default: 
+    default_function: 
+    collation: 
+    comment: 
+  - &6 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: comments_count
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: integer
+      type: :integer
+      limit: 
+      precision: 
+      scale: 
+    'null': true
+    default: '0'
+    default_function: 
+    collation: 
+    comment: 
+  - &7 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: taggings_with_delete_all_count
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: integer
+      type: :integer
+      limit: 
+      precision: 
+      scale: 
+    'null': true
+    default: '0'
+    default_function: 
+    collation: 
+    comment: 
+  - &8 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: taggings_with_destroy_count
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: integer
+      type: :integer
+      limit: 
+      precision: 
+      scale: 
+    'null': true
+    default: '0'
+    default_function: 
+    collation: 
+    comment: 
+  - &9 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: tags_count
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: integer
+      type: :integer
+      limit: 
+      precision: 
+      scale: 
+    'null': true
+    default: '0'
+    default_function: 
+    collation: 
+    comment: 
+  - &10 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: tags_with_destroy_count
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: integer
+      type: :integer
+      limit: 
+      precision: 
+      scale: 
+    'null': true
+    default: '0'
+    default_function: 
+    collation: 
+    comment: 
+  - &11 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: tags_with_nullify_count
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: integer
+      type: :integer
+      limit: 
+      precision: 
+      scale: 
+    'null': true
+    default: '0'
+    default_function: 
+    collation: 
+    comment: 
+columns_hash:
+  posts:
+    id: *1
+    author_id: *2
+    title: *3
+    body: *4
+    type: *5
+    comments_count: *6
+    taggings_with_delete_all_count: *7
+    taggings_with_destroy_count: *8
+    tags_count: *9
+    tags_with_destroy_count: *10
+    tags_with_nullify_count: *11
+primary_keys:
+  posts: id
+data_sources:
+  ar_internal_metadata: true
+  table_with_autoincrement: true
+  accounts: true
+  admin_accounts: true
+  admin_users: true
+  aircraft: true
+  articles: true
+  articles_magazines: true
+  articles_tags: true
+  audit_logs: true
+  authors: true
+  author_addresses: true
+  author_favorites: true
+  auto_id_tests: true
+  binaries: true
+  birds: true
+  books: true
+  booleans: true
+  bulbs: true
+  CamelCase: true
+  cars: true
+  carriers: true
+  categories: true
+  categories_posts: true
+  categorizations: true
+  citations: true
+  clubs: true
+  collections: true
+  colnametests: true
+  columns: true
+  comments: true
+  companies: true
+  content: true
+  content_positions: true
+  vegetables: true
+  computers: true
+  computers_developers: true
+  contracts: true
+  customers: true
+  customer_carriers: true
+  dashboards: true
+  developers: true
+  developers_projects: true
+  dog_lovers: true
+  dogs: true
+  doubloons: true
+  edges: true
+  engines: true
+  entrants: true
+  essays: true
+  events: true
+  eyes: true
+  funny_jokes: true
+  cold_jokes: true
+  friendships: true
+  goofy_string_id: true
+  having: true
+  guids: true
+  guitars: true
+  inept_wizards: true
+  integer_limits: true
+  invoices: true
+  iris: true
+  items: true
+  jobs: true
+  jobs_pool: true
+  keyboards: true
+  legacy_things: true
+  lessons: true
+  lessons_students: true
+  students: true
+  lint_models: true
+  line_items: true
+  lions: true
+  lock_without_defaults: true
+  lock_without_defaults_cust: true
+  magazines: true
+  mateys: true
+  members: true
+  member_details: true
+  member_friends: true
+  memberships: true
+  member_types: true
+  mentors: true
+  minivans: true
+  minimalistics: true
+  mixed_case_monkeys: true
+  mixins: true
+  movies: true
+  notifications: true
+  numeric_data: true
+  orders: true
+  organizations: true
+  owners: true
+  paint_colors: true
+  paint_textures: true
+  parrots: true
+  parrots_pirates: true
+  parrots_treasures: true
+  people: true
+  peoples_treasures: true
+  personal_legacy_things: true
+  pets: true
+  pets_treasures: true
+  pirates: true
+  posts: true
+  serialized_posts: true
+  images: true
+  price_estimates: true
+  products: true
+  product_types: true
+  projects: true
+  randomly_named_table1: true
+  randomly_named_table2: true
+  randomly_named_table3: true
+  ratings: true
+  readers: true
+  references: true
+  shape_expressions: true
+  ships: true
+  ship_parts: true
+  prisoners: true
+  shop_accounts: true
+  speedometers: true
+  sponsors: true
+  string_key_objects: true
+  subscribers: true
+  subscriptions: true
+  tags: true
+  taggings: true
+  tasks: true
+  topics: true
+  toys: true
+  traffic_lights: true
+  treasures: true
+  tuning_pegs: true
+  tyres: true
+  variants: true
+  vertices: true
+  warehouse-things: true
+  circles: true
+  squares: true
+  triangles: true
+  non_poly_ones: true
+  non_poly_twos: true
+  men: true
+  faces: true
+  interests: true
+  zines: true
+  wheels: true
+  countries: true
+  treaties: true
+  countries_treaties: true
+  liquid: true
+  molecules: true
+  electrons: true
+  weirds: true
+  nodes: true
+  trees: true
+  hotels: true
+  departments: true
+  cake_designers: true
+  drink_designers: true
+  chefs: true
+  recipes: true
+  records: true
+  overloaded_types: true
+  users: true
+  test_with_keyword_column_name: true
+  fk_test_has_pk: true
+  fk_test_has_fk: true
+version: 0
diff --git a/activerecord/test/cases/adapter_test.rb b/activerecord/test/cases/adapter_test.rb
index 8bcecf2ed3..3fce0a1df1 100644
--- a/activerecord/test/cases/adapter_test.rb
+++ b/activerecord/test/cases/adapter_test.rb
@@ -182,6 +182,14 @@ module ActiveRecord
       assert_not_nil error.cause
     end
 
+    def test_not_null_violations_are_translated_to_specific_exception
+      error = assert_raises(ActiveRecord::NotNullViolation) do
+        Post.create
+      end
+
+      assert_not_nil error.cause
+    end
+
     unless current_adapter?(:SQLite3Adapter)
       def test_foreign_key_violations_are_translated_to_specific_exception
         error = assert_raises(ActiveRecord::InvalidForeignKey) do
@@ -218,6 +226,14 @@ module ActiveRecord
 
         assert_not_nil error.cause
       end
+
+      def test_numeric_value_out_of_ranges_are_translated_to_specific_exception
+        error = assert_raises(ActiveRecord::RangeError) do
+          Book.connection.create("INSERT INTO books(author_id) VALUES (2147483648)")
+        end
+
+        assert_not_nil error.cause
+      end
     end
 
     def test_disable_referential_integrity
@@ -269,13 +285,13 @@ module ActiveRecord
 
     unless current_adapter?(:PostgreSQLAdapter)
       def test_log_invalid_encoding
-        error = assert_raise ActiveRecord::StatementInvalid do
+        error = assert_raises RuntimeError do
           @connection.send :log, "SELECT 'ы' FROM DUAL" do
             raise "ы".force_encoding(Encoding::ASCII_8BIT)
           end
         end
 
-        assert_not_nil error.cause
+        assert_not_nil error.message
       end
     end
 
diff --git a/activerecord/test/cases/adapters/mysql2/active_schema_test.rb b/activerecord/test/cases/adapters/mysql2/active_schema_test.rb
index a70eb5a094..2a528b2cb1 100644
--- a/activerecord/test/cases/adapters/mysql2/active_schema_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/active_schema_test.rb
@@ -28,12 +28,15 @@ class Mysql2ActiveSchemaTest < ActiveRecord::Mysql2TestCase
 
     expected = "CREATE  INDEX `index_people_on_last_name_and_first_name`  ON `people` (`last_name`(15), `first_name`(15)) "
     assert_equal expected, add_index(:people, [:last_name, :first_name], length: 15)
+    assert_equal expected, add_index(:people, ["last_name", "first_name"], length: 15)
 
     expected = "CREATE  INDEX `index_people_on_last_name_and_first_name`  ON `people` (`last_name`(15), `first_name`) "
     assert_equal expected, add_index(:people, [:last_name, :first_name], length: { last_name: 15 })
+    assert_equal expected, add_index(:people, ["last_name", "first_name"], length: { last_name: 15 })
 
     expected = "CREATE  INDEX `index_people_on_last_name_and_first_name`  ON `people` (`last_name`(15), `first_name`(10)) "
     assert_equal expected, add_index(:people, [:last_name, :first_name], length: { last_name: 15, first_name: 10 })
+    assert_equal expected, add_index(:people, ["last_name", :first_name], length: { last_name: 15, "first_name" => 10 })
 
     %w(SPATIAL FULLTEXT UNIQUE).each do |type|
       expected = "CREATE #{type} INDEX `index_people_on_last_name`  ON `people` (`last_name`) "
diff --git a/activerecord/test/cases/adapters/mysql2/connection_test.rb b/activerecord/test/cases/adapters/mysql2/connection_test.rb
index 9c109d8a24..c1de2218e2 100644
--- a/activerecord/test/cases/adapters/mysql2/connection_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/connection_test.rb
@@ -186,7 +186,7 @@ class Mysql2ConnectionTest < ActiveRecord::Mysql2TestCase
       "expected release_advisory_lock to return false when there was no lock to release"
   end
 
-  protected
+  private
 
     def test_lock_free(lock_name)
       @connection.select_value("SELECT IS_FREE_LOCK(#{@connection.quote(lock_name)})") == 1
diff --git a/activerecord/test/cases/adapters/mysql2/json_test.rb b/activerecord/test/cases/adapters/mysql2/json_test.rb
index 5d4db1be91..6954006003 100644
--- a/activerecord/test/cases/adapters/mysql2/json_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/json_test.rb
@@ -93,7 +93,7 @@ if ActiveRecord::Base.connection.supports_json?
     def test_null_json
       @connection.execute "insert into json_data_type (payload) VALUES(null)"
       x = JsonDataType.first
-      assert_equal(nil, x.payload)
+      assert_nil(x.payload)
     end
 
     def test_select_array_json_value
@@ -111,7 +111,7 @@ if ActiveRecord::Base.connection.supports_json?
     def test_select_nil_json_after_update
       json = JsonDataType.create(payload: "foo")
       x = JsonDataType.where(payload: nil).first
-      assert_equal(nil, x)
+      assert_nil(x)
 
       json.update_attributes payload: nil
       x = JsonDataType.where(payload: nil).first
diff --git a/activerecord/test/cases/adapters/mysql2/legacy_migration_test.rb b/activerecord/test/cases/adapters/mysql2/legacy_migration_test.rb
new file mode 100644
index 0000000000..5d3125c2be
--- /dev/null
+++ b/activerecord/test/cases/adapters/mysql2/legacy_migration_test.rb
@@ -0,0 +1,60 @@
+require "cases/helper"
+
+class MysqlLegacyMigrationTest < ActiveRecord::Mysql2TestCase
+  self.use_transactional_tests = false
+
+  class GenerateTableWithoutBigint < ActiveRecord::Migration[5.0]
+    def change
+      create_table :legacy_integer_pk do |table|
+        table.string :foo
+      end
+
+      create_table :override_pk, id: :bigint do |table|
+        table.string :bar
+      end
+    end
+  end
+
+  def setup
+    super
+    @connection = ActiveRecord::Base.connection
+
+    @migration_verbose_old = ActiveRecord::Migration.verbose
+    ActiveRecord::Migration.verbose = false
+
+    migrations = [GenerateTableWithoutBigint.new(nil, 1)]
+
+    ActiveRecord::Migrator.new(:up, migrations).migrate
+  end
+
+  def teardown
+    ActiveRecord::Migration.verbose = @migration_verbose_old
+    @connection.drop_table("legacy_integer_pk")
+    @connection.drop_table("override_pk")
+    ActiveRecord::SchemaMigration.delete_all rescue nil
+    super
+  end
+
+  def test_create_table_uses_integer_as_pkey_by_default
+    col = column(:legacy_integer_pk, :id)
+    assert_equal "int(11)", sql_type_for(col)
+    assert col.auto_increment?
+  end
+
+  def test_create_tables_respects_pk_column_type_override
+    col = column(:override_pk, :id)
+    assert_equal "bigint(20)", sql_type_for(col)
+  end
+
+  private
+
+    def column(table_name, column_name)
+      ActiveRecord::Base.connection
+        .columns(table_name.to_s)
+        .detect { |c| c.name == column_name.to_s }
+    end
+
+    def sql_type_for(col)
+      col && col.sql_type
+    end
+end
diff --git a/activerecord/test/cases/adapters/mysql2/mysql2_adapter_test.rb b/activerecord/test/cases/adapters/mysql2/mysql2_adapter_test.rb
index 69336eb906..aab3dcb724 100644
--- a/activerecord/test/cases/adapters/mysql2/mysql2_adapter_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/mysql2_adapter_test.rb
@@ -65,6 +65,19 @@ class Mysql2AdapterTest < ActiveRecord::Mysql2TestCase
       @conn.columns_for_distinct("posts.id", [order])
   end
 
+  def test_errors_for_bigint_fks_on_integer_pk_table
+    # table old_cars has primary key of integer
+
+    error = assert_raises(ActiveRecord::MismatchedForeignKey) do
+      @conn.add_reference :engines, :old_car
+      @conn.add_foreign_key :engines, :old_cars
+    end
+
+    assert_match "Column `old_car_id` on table `engines` has a type of `bigint(20)`", error.message
+    assert_not_nil error.cause
+    @conn.exec_query("ALTER TABLE engines DROP COLUMN old_car_id")
+  end
+
   private
 
     def with_example_table(definition = "id int auto_increment primary key, number int, data varchar(255)", &block)
diff --git a/activerecord/test/cases/adapters/mysql2/reserved_word_test.rb b/activerecord/test/cases/adapters/mysql2/reserved_word_test.rb
index b400f4d2f9..2c778b1150 100644
--- a/activerecord/test/cases/adapters/mysql2/reserved_word_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/reserved_word_test.rb
@@ -143,7 +143,7 @@ class Mysql2ReservedWordTest < ActiveRecord::Mysql2TestCase
     end
 
     # custom create table, uses execute on connection to create a table, note: escapes table_name, does NOT escape columns
-    def create_tables_directly (tables, connection = @connection)
+    def create_tables_directly(tables, connection = @connection)
       tables.each do |table_name, column_properties|
         connection.execute("CREATE TABLE `#{table_name}` ( #{column_properties} )")
       end
diff --git a/activerecord/test/cases/adapters/mysql2/unsigned_type_test.rb b/activerecord/test/cases/adapters/mysql2/unsigned_type_test.rb
index 59475ad177..a0823be143 100644
--- a/activerecord/test/cases/adapters/mysql2/unsigned_type_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/unsigned_type_test.rb
@@ -15,6 +15,7 @@ class Mysql2UnsignedTypeTest < ActiveRecord::Mysql2TestCase
       t.bigint  :unsigned_bigint,  unsigned: true
       t.float   :unsigned_float,   unsigned: true
       t.decimal :unsigned_decimal, unsigned: true, precision: 10, scale: 2
+      t.column  :unsigned_zerofill, "int unsigned zerofill"
     end
   end
 
@@ -34,10 +35,10 @@ class Mysql2UnsignedTypeTest < ActiveRecord::Mysql2TestCase
     assert_raise(ActiveModel::RangeError) do
       UnsignedType.create(unsigned_bigint: -10)
     end
-    assert_raise(ActiveRecord::StatementInvalid) do
+    assert_raise(ActiveRecord::RangeError) do
       UnsignedType.create(unsigned_float: -10.0)
     end
-    assert_raise(ActiveRecord::StatementInvalid) do
+    assert_raise(ActiveRecord::RangeError) do
       UnsignedType.create(unsigned_decimal: -10.0)
     end
   end
@@ -48,7 +49,6 @@ class Mysql2UnsignedTypeTest < ActiveRecord::Mysql2TestCase
       t.unsigned_bigint  :unsigned_bigint_t
       t.unsigned_float   :unsigned_float_t
       t.unsigned_decimal :unsigned_decimal_t, precision: 10, scale: 2
-      t.column :unsigned_zerofill, "int unsigned zerofill"
     end
 
     @connection.columns("unsigned_types").select { |c| /^unsigned_/.match?(c.name) }.each do |column|
diff --git a/activerecord/test/cases/adapters/postgresql/active_schema_test.rb b/activerecord/test/cases/adapters/postgresql/active_schema_test.rb
index d3c65f3d94..b787de8453 100644
--- a/activerecord/test/cases/adapters/postgresql/active_schema_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/active_schema_test.rb
@@ -39,6 +39,10 @@ class PostgresqlActiveSchemaTest < ActiveRecord::PostgreSQLTestCase
     expected = %(CREATE  INDEX CONCURRENTLY "index_people_on_last_name" ON "people"  ("last_name"))
     assert_equal expected, add_index(:people, :last_name, algorithm: :concurrently)
 
+    expected = %(CREATE  INDEX  "index_people_on_last_name_and_first_name" ON "people"  ("last_name" DESC, "first_name" ASC))
+    assert_equal expected, add_index(:people, [:last_name, :first_name], order: { last_name: :desc, first_name: :asc })
+    assert_equal expected, add_index(:people, ["last_name", :first_name], order: { last_name: :desc, "first_name" => :asc })
+
     %w(gin gist hash btree).each do |type|
       expected = %(CREATE  INDEX  "index_people_on_last_name" ON "people" USING #{type} ("last_name"))
       assert_equal expected, add_index(:people, :last_name, using: type)
diff --git a/activerecord/test/cases/adapters/postgresql/bytea_test.rb b/activerecord/test/cases/adapters/postgresql/bytea_test.rb
index dc0df8715a..5c207116c4 100644
--- a/activerecord/test/cases/adapters/postgresql/bytea_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/bytea_test.rb
@@ -52,7 +52,7 @@ class PostgresqlByteaTest < ActiveRecord::PostgreSQLTestCase
   end
 
   def test_type_case_nil
-    assert_equal(nil, @type.deserialize(nil))
+    assert_nil(@type.deserialize(nil))
   end
 
   def test_read_value
@@ -66,7 +66,7 @@ class PostgresqlByteaTest < ActiveRecord::PostgreSQLTestCase
   def test_read_nil_value
     @connection.execute "insert into bytea_data_type (payload) VALUES (null)"
     record = ByteaDataType.first
-    assert_equal(nil, record.payload)
+    assert_nil(record.payload)
     record.delete
   end
 
@@ -106,8 +106,8 @@ class PostgresqlByteaTest < ActiveRecord::PostgreSQLTestCase
   def test_write_nil
     record = ByteaDataType.create(payload: nil)
     assert_not record.new_record?
-    assert_equal(nil, record.payload)
-    assert_equal(nil, ByteaDataType.where(id: record.id).first.payload)
+    assert_nil(record.payload)
+    assert_nil(ByteaDataType.where(id: record.id).first.payload)
   end
 
   class Serializer
diff --git a/activerecord/test/cases/adapters/postgresql/connection_test.rb b/activerecord/test/cases/adapters/postgresql/connection_test.rb
index 48c82cb7b9..45aa748ffc 100644
--- a/activerecord/test/cases/adapters/postgresql/connection_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/connection_test.rb
@@ -245,7 +245,7 @@ module ActiveRecord
       end
     end
 
-    protected
+    private
 
       def with_warning_suppression
         log_level = @connection.client_min_messages
diff --git a/activerecord/test/cases/adapters/postgresql/geometric_test.rb b/activerecord/test/cases/adapters/postgresql/geometric_test.rb
index a65d4d1ad9..c1f3a4ae2c 100644
--- a/activerecord/test/cases/adapters/postgresql/geometric_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/geometric_test.rb
@@ -96,7 +96,7 @@ class PostgresqlPointTest < ActiveRecord::PostgreSQLTestCase
     assert_nothing_raised { PostgresqlPoint.new(x: "") }
 
     p = PostgresqlPoint.new(x: "")
-    assert_equal nil, p.x
+    assert_nil p.x
   end
 
   def test_array_of_points_round_trip
diff --git a/activerecord/test/cases/adapters/postgresql/json_test.rb b/activerecord/test/cases/adapters/postgresql/json_test.rb
index 991dedfdf1..93558ac4d2 100644
--- a/activerecord/test/cases/adapters/postgresql/json_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/json_test.rb
@@ -110,7 +110,7 @@ module PostgresqlJSONSharedTestCases
   def test_null_json
     @connection.execute "insert into json_data_type (payload) VALUES(null)"
     x = JsonDataType.first
-    assert_equal(nil, x.payload)
+    assert_nil(x.payload)
   end
 
   def test_select_nil_json_after_create
@@ -122,7 +122,7 @@ module PostgresqlJSONSharedTestCases
   def test_select_nil_json_after_update
     json = JsonDataType.create(payload: "foo")
     x = JsonDataType.where(payload: nil).first
-    assert_equal(nil, x)
+    assert_nil(x)
 
     json.update_attributes payload: nil
     x = JsonDataType.where(payload: nil).first
diff --git a/activerecord/test/cases/adapters/postgresql/legacy_migration_test.rb b/activerecord/test/cases/adapters/postgresql/legacy_migration_test.rb
new file mode 100644
index 0000000000..082fe95053
--- /dev/null
+++ b/activerecord/test/cases/adapters/postgresql/legacy_migration_test.rb
@@ -0,0 +1,54 @@
+require "cases/helper"
+
+class PostgresqlLegacyMigrationTest < ActiveRecord::PostgreSQLTestCase
+  class GenerateTableWithoutBigserial < ActiveRecord::Migration[5.0]
+    def change
+      create_table :legacy_integer_pk do |table|
+        table.string :foo
+      end
+
+      create_table :override_pk, id: :bigint do |table|
+        table.string :bar
+      end
+    end
+  end
+
+  def setup
+    super
+
+    @migration_verbose_old = ActiveRecord::Migration.verbose
+    ActiveRecord::Migration.verbose = false
+
+    migrations = [GenerateTableWithoutBigserial.new(nil, 1)]
+    ActiveRecord::Migrator.new(:up, migrations).migrate
+  end
+
+  def teardown
+    ActiveRecord::Migration.verbose = @migration_verbose_old
+
+    super
+  end
+
+  def test_create_table_uses_serial_as_pkey_by_default
+    col = column(:legacy_integer_pk, :id)
+    assert_equal "integer", sql_type_for(col)
+    assert col.serial?
+  end
+
+  def test_create_tables_respects_pk_column_type_override
+    col = column(:override_pk, :id)
+    assert_equal "bigint", sql_type_for(col)
+  end
+
+  private
+
+    def column(table_name, column_name)
+      ActiveRecord::Base.connection.
+        columns(table_name.to_s).
+        detect { |c| c.name == column_name.to_s }
+    end
+
+    def sql_type_for(col)
+      col && col.sql_type
+    end
+end
diff --git a/activerecord/test/cases/adapters/postgresql/quoting_test.rb b/activerecord/test/cases/adapters/postgresql/quoting_test.rb
index a9e81ab3d8..141baffa5b 100644
--- a/activerecord/test/cases/adapters/postgresql/quoting_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/quoting_test.rb
@@ -36,7 +36,7 @@ module ActiveRecord
         def test_quote_bit_string
           value = "'); SELECT * FROM users; /*\n01\n*/--"
           type = OID::Bit.new
-          assert_equal nil, @conn.quote(type.serialize(value))
+          assert_nil @conn.quote(type.serialize(value))
         end
       end
     end
diff --git a/activerecord/test/cases/adapters/postgresql/transaction_test.rb b/activerecord/test/cases/adapters/postgresql/transaction_test.rb
index f130e344c4..9b42d0383d 100644
--- a/activerecord/test/cases/adapters/postgresql/transaction_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/transaction_test.rb
@@ -89,7 +89,7 @@ module ActiveRecord
       end
     end
 
-    protected
+    private
 
       def with_warning_suppression
         log_level = ActiveRecord::Base.connection.client_min_messages
diff --git a/activerecord/test/cases/adapters/postgresql/utils_test.rb b/activerecord/test/cases/adapters/postgresql/utils_test.rb
index 7f6ea3887d..9f9e3bda2f 100644
--- a/activerecord/test/cases/adapters/postgresql/utils_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/utils_test.rb
@@ -56,7 +56,7 @@ class PostgreSQLNameTest < ActiveRecord::PostgreSQLTestCase
   test "can be used as hash key" do
     hash = { Name.new("schema", "article_seq") => "success" }
     assert_equal "success", hash[Name.new("schema", "article_seq")]
-    assert_equal nil, hash[Name.new("schema", "articles")]
-    assert_equal nil, hash[Name.new("public", "article_seq")]
+    assert_nil hash[Name.new("schema", "articles")]
+    assert_nil hash[Name.new("public", "article_seq")]
   end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/uuid_test.rb b/activerecord/test/cases/adapters/postgresql/uuid_test.rb
index 4604c2eb3b..f34d50e25c 100644
--- a/activerecord/test/cases/adapters/postgresql/uuid_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/uuid_test.rb
@@ -71,12 +71,12 @@ class PostgresqlUUIDTest < ActiveRecord::PostgreSQLTestCase
 
   def test_treat_blank_uuid_as_nil
     UUIDType.create! guid: ""
-    assert_equal(nil, UUIDType.last.guid)
+    assert_nil(UUIDType.last.guid)
   end
 
   def test_treat_invalid_uuid_as_nil
     uuid = UUIDType.create! guid: "foobar"
-    assert_equal(nil, uuid.guid)
+    assert_nil(uuid.guid)
   end
 
   def test_invalid_uuid_dont_modify_before_type_cast
@@ -210,7 +210,7 @@ class PostgresqlUUIDGenerationTest < ActiveRecord::PostgreSQLTestCase
     def test_pk_and_sequence_for_uuid_primary_key
       pk, seq = connection.pk_and_sequence_for("pg_uuids")
       assert_equal "id", pk
-      assert_equal nil, seq
+      assert_nil seq
     end
 
     def test_schema_dumper_for_uuid_primary_key
diff --git a/activerecord/test/cases/adapters/sqlite3/copy_table_test.rb b/activerecord/test/cases/adapters/sqlite3/copy_table_test.rb
index 8342b05870..91967c1e33 100644
--- a/activerecord/test/cases/adapters/sqlite3/copy_table_test.rb
+++ b/activerecord/test/cases/adapters/sqlite3/copy_table_test.rb
@@ -75,7 +75,7 @@ class CopyTableTest < ActiveRecord::SQLite3TestCase
     test_copy_table "binaries", "binaries2"
   end
 
-protected
+private
   def copy_table(from, to, options = {})
     @connection.copy_table(from, to, { temporary: true }.merge(options))
   end
diff --git a/activerecord/test/cases/adapters/sqlite3/legacy_migration_test.rb b/activerecord/test/cases/adapters/sqlite3/legacy_migration_test.rb
new file mode 100644
index 0000000000..fcca8d66b5
--- /dev/null
+++ b/activerecord/test/cases/adapters/sqlite3/legacy_migration_test.rb
@@ -0,0 +1,59 @@
+require "cases/helper"
+
+class SqliteLegacyMigrationTest < ActiveRecord::SQLite3TestCase
+  self.use_transactional_tests = false
+
+  class GenerateTableWithoutBigint < ActiveRecord::Migration[5.0]
+    def change
+      create_table :legacy_integer_pk do |table|
+        table.string :foo
+      end
+
+      create_table :override_pk, id: :bigint do |table|
+        table.string :bar
+      end
+    end
+  end
+
+  def setup
+    super
+    @connection = ActiveRecord::Base.connection
+
+    @migration_verbose_old = ActiveRecord::Migration.verbose
+    ActiveRecord::Migration.verbose = false
+
+    migrations = [GenerateTableWithoutBigint.new(nil, 1)]
+
+    ActiveRecord::Migrator.new(:up, migrations).migrate
+  end
+
+  def teardown
+    ActiveRecord::Migration.verbose = @migration_verbose_old
+    @connection.drop_table("legacy_integer_pk")
+    @connection.drop_table("override_pk")
+    ActiveRecord::SchemaMigration.delete_all rescue nil
+    super
+  end
+
+  def test_create_table_uses_integer_as_pkey_by_default
+    col = column(:legacy_integer_pk, :id)
+    assert_equal "INTEGER", sql_type_for(col)
+    assert primary_key?(:legacy_integer_pk, "id"), "id is not primary key"
+  end
+
+  private
+
+    def column(table_name, column_name)
+      ActiveRecord::Base.connection
+        .columns(table_name.to_s)
+        .detect { |c| c.name == column_name.to_s }
+    end
+
+    def sql_type_for(col)
+      col && col.sql_type
+    end
+
+    def primary_key?(table_name, column)
+      ActiveRecord::Base.connection.execute("PRAGMA table_info(#{table_name})").find { |col| col["name"] == column }["pk"] == 1
+    end
+end
diff --git a/activerecord/test/cases/adapters/sqlite3/quoting_test.rb b/activerecord/test/cases/adapters/sqlite3/quoting_test.rb
index 80a37e83ff..9750840051 100644
--- a/activerecord/test/cases/adapters/sqlite3/quoting_test.rb
+++ b/activerecord/test/cases/adapters/sqlite3/quoting_test.rb
@@ -37,7 +37,7 @@ class SQLite3QuotingTest < ActiveRecord::SQLite3TestCase
   end
 
   def test_type_cast_nil
-    assert_equal nil, @conn.type_cast(nil)
+    assert_nil @conn.type_cast(nil)
   end
 
   def test_type_cast_true
diff --git a/activerecord/test/cases/associations/belongs_to_associations_test.rb b/activerecord/test/cases/associations/belongs_to_associations_test.rb
index 72f1b3b125..b75e2a47a6 100644
--- a/activerecord/test/cases/associations/belongs_to_associations_test.rb
+++ b/activerecord/test/cases/associations/belongs_to_associations_test.rb
@@ -1057,7 +1057,7 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     comment.parent = nil
     comment.save!
 
-    assert_equal nil, comment.reload.parent
+    assert_nil comment.reload.parent
     assert_equal 0, comments(:greetings).reload.children_count
   end
 
@@ -1072,6 +1072,20 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     assert_equal 1, parent.reload.children_count
   end
 
+  def test_belongs_to_with_out_of_range_value_assigning
+    model = Class.new(Comment) do
+      def self.name; "Temp"; end
+      validates :post, presence: true
+    end
+
+    comment = model.new
+    comment.post_id = 9223372036854775808 # out of range in the bigint
+
+    assert_nil comment.post
+    assert_not comment.valid?
+    assert_equal [{ error: :blank }], comment.errors.details[:post]
+  end
+
   def test_polymorphic_with_custom_primary_key
     toy = Toy.create!
     sponsor = Sponsor.create!(sponsorable: toy)
diff --git a/activerecord/test/cases/associations/eager_load_nested_include_test.rb b/activerecord/test/cases/associations/eager_load_nested_include_test.rb
index ed1b0f5226..e9f551b6b2 100644
--- a/activerecord/test/cases/associations/eager_load_nested_include_test.rb
+++ b/activerecord/test/cases/associations/eager_load_nested_include_test.rb
@@ -12,7 +12,7 @@ module Remembered
 
   included do
     after_create :remember
-  protected
+  private
     def remember; self.class.remembered << self; end
   end
 
diff --git a/activerecord/test/cases/associations/eager_test.rb b/activerecord/test/cases/associations/eager_test.rb
index dc04ccdccc..ff1bf8acd4 100644
--- a/activerecord/test/cases/associations/eager_test.rb
+++ b/activerecord/test/cases/associations/eager_test.rb
@@ -241,7 +241,7 @@ class EagerAssociationTest < ActiveRecord::TestCase
     post = assert_queries(1) { Post.all.merge!(includes: { author_with_address: :author_address }).find(post.id) }
     # find the post, then find the author which is null so no query for the author or address
     assert_no_queries do
-      assert_equal nil, post.author_with_address
+      assert_nil post.author_with_address
     end
   end
 
@@ -250,7 +250,7 @@ class EagerAssociationTest < ActiveRecord::TestCase
     sponsor.update!(sponsorable: nil)
     sponsor = assert_queries(1) { Sponsor.all.merge!(includes: :sponsorable).find(sponsor.id) }
     assert_no_queries do
-      assert_equal nil, sponsor.sponsorable
+      assert_nil sponsor.sponsorable
     end
   end
 
@@ -261,7 +261,7 @@ class EagerAssociationTest < ActiveRecord::TestCase
       assert_nothing_raised { Sponsor.all.merge!(includes: :sponsorable).find(sponsor.id) }
     end
     assert_no_queries do
-      assert_equal nil, sponsor.sponsorable
+      assert_nil sponsor.sponsorable
     end
   end
 
diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index d657be71cc..482b086e5c 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -187,7 +187,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     ship.parts.clear
     part.reload
 
-    assert_equal nil, part.ship
+    assert_nil part.ship
     assert !part.updated_at_changed?
   end
 
@@ -2475,7 +2475,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   test "double insertion of new object to association when same association used in the after create callback of a new object" do
     reset_callbacks(:save, Bulb) do
-      Bulb.after_save { |record| record.car.bulbs.to_a }
+      Bulb.after_save { |record| record.car.bulbs.load }
       car = Car.create!
       car.bulbs << Bulb.new
       assert_equal 1, car.bulbs.size
diff --git a/activerecord/test/cases/associations/has_many_through_associations_test.rb b/activerecord/test/cases/associations/has_many_through_associations_test.rb
index 8defb09db7..fd79d4a5f9 100644
--- a/activerecord/test/cases/associations/has_many_through_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_through_associations_test.rb
@@ -402,7 +402,7 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
       end
     end
 
-    assert_equal nil, reference.reload.job_id
+    assert_nil reference.reload.job_id
   ensure
     Reference.make_comments = false
   end
@@ -423,7 +423,7 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     end
 
     # Check that the destroy callback on Reference did not run
-    assert_equal nil, person.reload.comments
+    assert_nil person.reload.comments
   ensure
     Reference.make_comments = false
   end
@@ -485,7 +485,7 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     end
 
     references.each do |reference|
-      assert_equal nil, reference.reload.job_id
+      assert_nil reference.reload.job_id
     end
   end
 
@@ -904,6 +904,13 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     assert_match(/Couldn't find all Clients with 'name'/, e.message)
   end
 
+  def test_collection_singular_ids_through_setter_raises_exception_when_invalid_ids_set
+    author = authors(:david)
+    ids = [categories(:general).name, "Unknown"]
+    e = assert_raises(ActiveRecord::RecordNotFound) { author.essay_category_ids = ids }
+    assert_equal "Couldn't find all Categories with 'name': (General, Unknown) (found 1 results, but was looking for 2)", e.message
+  end
+
   def test_build_a_model_from_hm_through_association_with_where_clause
     assert_nothing_raised { books(:awdr).subscribers.where(nick: "marklazz").build }
   end
diff --git a/activerecord/test/cases/associations/has_one_through_associations_test.rb b/activerecord/test/cases/associations/has_one_through_associations_test.rb
index 6ba062a248..432c3526a5 100644
--- a/activerecord/test/cases/associations/has_one_through_associations_test.rb
+++ b/activerecord/test/cases/associations/has_one_through_associations_test.rb
@@ -82,7 +82,7 @@ class HasOneThroughAssociationsTest < ActiveRecord::TestCase
   def test_set_record_to_nil_should_delete_association
     @member.club = nil
     @member.reload
-    assert_equal nil, @member.current_membership
+    assert_nil @member.current_membership
     assert_nil @member.club
   end
 
@@ -110,12 +110,12 @@ class HasOneThroughAssociationsTest < ActiveRecord::TestCase
     # conditions on the through table
     assert_equal clubs(:moustache_club), Member.all.merge!(includes: :favourite_club).find(@member.id).favourite_club
     memberships(:membership_of_favourite_club).update_columns(favourite: false)
-    assert_equal nil,                    Member.all.merge!(includes: :favourite_club).find(@member.id).reload.favourite_club
+    assert_nil Member.all.merge!(includes: :favourite_club).find(@member.id).reload.favourite_club
 
     # conditions on the source table
     assert_equal clubs(:moustache_club), Member.all.merge!(includes: :hairy_club).find(@member.id).hairy_club
     clubs(:moustache_club).update_columns(name: "Association of Clean-Shaven Persons")
-    assert_equal nil,                    Member.all.merge!(includes: :hairy_club).find(@member.id).reload.hairy_club
+    assert_nil Member.all.merge!(includes: :hairy_club).find(@member.id).reload.hairy_club
   end
 
   def test_has_one_through_polymorphic_with_source_type
diff --git a/activerecord/test/cases/attribute_methods_test.rb b/activerecord/test/cases/attribute_methods_test.rb
index ba6877a6a6..3dc0c0ce53 100644
--- a/activerecord/test/cases/attribute_methods_test.rb
+++ b/activerecord/test/cases/attribute_methods_test.rb
@@ -92,7 +92,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
 
   test "attribute keys on a new instance" do
     t = Topic.new
-    assert_equal nil, t.title, "The topics table has a title column, so it should be nil"
+    assert_nil t.title, "The topics table has a title column, so it should be nil"
     assert_raise(NoMethodError) { t.title2 }
   end
 
@@ -156,7 +156,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     keyboard = Keyboard.create
     keyboard.key_number = "10"
     assert_equal "10", keyboard.id_before_type_cast
-    assert_equal nil, keyboard.read_attribute_before_type_cast("id")
+    assert_nil keyboard.read_attribute_before_type_cast("id")
     assert_equal "10", keyboard.read_attribute_before_type_cast("key_number")
     assert_equal "10", keyboard.read_attribute_before_type_cast(:key_number)
   end
@@ -213,7 +213,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
 
       record.written_on = "345643456"
       assert_equal "345643456", record.written_on_before_type_cast
-      assert_equal nil, record.written_on
+      assert_nil record.written_on
 
       record.written_on = "2009-10-11 12:13:14"
       assert_equal "2009-10-11 12:13:14", record.written_on_before_type_cast
@@ -319,6 +319,13 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert_equal "Still another topic: part 4", topic.title
   end
 
+  test "write_attribute can write aliased attributes as well" do
+    topic = Topic.new(title: "Don't change the topic")
+    topic.write_attribute :heading, "New topic"
+
+    assert_equal "New topic", topic.title
+  end
+
   test "read_attribute" do
     topic = Topic.new
     topic.title = "Don't change the topic"
@@ -329,6 +336,16 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert_equal "Don't change the topic", topic[:title]
   end
 
+  test "read_attribute can read aliased attributes as well" do
+    topic = Topic.new(title: "Don't change the topic")
+
+    assert_equal "Don't change the topic", topic.read_attribute("heading")
+    assert_equal "Don't change the topic", topic["heading"]
+
+    assert_equal "Don't change the topic", topic.read_attribute(:heading)
+    assert_equal "Don't change the topic", topic[:heading]
+  end
+
   test "read_attribute raises ActiveModel::MissingAttributeError when the attribute does not exist" do
     computer = Computer.select("id").first
     assert_raises(ActiveModel::MissingAttributeError) { computer[:developer] }
@@ -737,7 +754,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
   test "time zone-aware attributes do not recurse infinitely on invalid values" do
     in_time_zone "Pacific Time (US & Canada)" do
       record = @target.new(bonus_time: [])
-      assert_equal nil, record.bonus_time
+      assert_nil record.bonus_time
     end
   end
 
diff --git a/activerecord/test/cases/attribute_set_test.rb b/activerecord/test/cases/attribute_set_test.rb
index 059b5b2401..bd4b200735 100644
--- a/activerecord/test/cases/attribute_set_test.rb
+++ b/activerecord/test/cases/attribute_set_test.rb
@@ -25,7 +25,7 @@ module ActiveRecord
       attributes = builder.build_from_database(foo: "3.3")
 
       assert_equal "3.3", attributes[:foo].value_before_type_cast
-      assert_equal nil, attributes[:bar].value_before_type_cast
+      assert_nil attributes[:bar].value_before_type_cast
       assert_equal :bar, attributes[:bar].name
     end
 
diff --git a/activerecord/test/cases/autosave_association_test.rb b/activerecord/test/cases/autosave_association_test.rb
index a3f82ed49d..6d31b7a091 100644
--- a/activerecord/test/cases/autosave_association_test.rb
+++ b/activerecord/test/cases/autosave_association_test.rb
@@ -36,11 +36,11 @@ class TestAutosaveAssociationsInGeneral < ActiveRecord::TestCase
 
       private
 
-      def should_be_cool
-        unless self.first_name == "cool"
-          errors.add :first_name, "not cool"
+        def should_be_cool
+          unless self.first_name == "cool"
+            errors.add :first_name, "not cool"
+          end
         end
-      end
     }
     reference = Class.new(ActiveRecord::Base) {
       self.table_name = "references"
@@ -1391,6 +1391,14 @@ module AutosaveAssociationOnACollectionAssociationTests
     assert_equal "Squawky", parrot.reload.name
   end
 
+  def test_should_not_update_children_when_parent_creation_with_no_reason
+    parrot = Parrot.create!(name: "Polly")
+    assert_equal 0, parrot.updated_count
+
+    Pirate.create!(parrot_ids: [parrot.id], catchphrase: "Arrrr")
+    assert_equal 0, parrot.reload.updated_count
+  end
+
   def test_should_automatically_validate_the_associated_models
     @pirate.send(@association_name).each { |child| child.name = "" }
 
@@ -1699,3 +1707,27 @@ class TestAutosaveAssociationWithTouch < ActiveRecord::TestCase
     assert_nothing_raised { invoice.line_items.create(amount: 10) }
   end
 end
+
+class TestAutosaveAssociationOnAHasManyAssociationWithInverse < ActiveRecord::TestCase
+  class Post < ActiveRecord::Base
+    has_many :comments, inverse_of: :post
+  end
+
+  class Comment < ActiveRecord::Base
+    belongs_to :post, inverse_of: :comments
+
+    attr_accessor :post_comments_count
+    after_save do
+      self.post_comments_count = post.comments.count
+    end
+  end
+
+  def test_after_save_callback_with_autosave
+    post = Post.new(title: "Test", body: "...")
+    comment = post.comments.build(body: "...")
+    post.save!
+
+    assert_equal 1, post.comments.count
+    assert_equal 1, comment.post_comments_count
+  end
+end
diff --git a/activerecord/test/cases/base_test.rb b/activerecord/test/cases/base_test.rb
index 4e9d78de5d..ad9bc60944 100644
--- a/activerecord/test/cases/base_test.rb
+++ b/activerecord/test/cases/base_test.rb
@@ -622,7 +622,7 @@ class BasicsTest < ActiveRecord::TestCase
       Topic.find(topic.id).destroy
     end
 
-    assert_equal nil, Topic.find_by_id(topic.id)
+    assert_nil Topic.find_by_id(topic.id)
   end
 
   def test_comparison_with_different_objects
diff --git a/activerecord/test/cases/callbacks_test.rb b/activerecord/test/cases/callbacks_test.rb
index 4b517e9d70..11ec6fb2c5 100644
--- a/activerecord/test/cases/callbacks_test.rb
+++ b/activerecord/test/cases/callbacks_test.rb
@@ -449,7 +449,7 @@ class CallbacksTest < ActiveRecord::TestCase
       assert david.valid?
       assert !david.save
       exc = assert_raise(ActiveRecord::RecordNotSaved) { david.save! }
-      assert_equal exc.record, david
+      assert_equal david, exc.record
       assert_equal "Failed to save the record", exc.message
     end
 
@@ -493,7 +493,7 @@ class CallbacksTest < ActiveRecord::TestCase
     assert_deprecated do
       assert !david.destroy
       exc = assert_raise(ActiveRecord::RecordNotDestroyed) { david.destroy! }
-      assert_equal exc.record, david
+      assert_equal david, exc.record
       assert_equal "Failed to destroy the record", exc.message
     end
     assert_not_nil ImmutableDeveloper.find_by_id(1)
@@ -527,7 +527,7 @@ class CallbacksTest < ActiveRecord::TestCase
     assert david.valid?
     assert !david.save
     exc = assert_raise(ActiveRecord::RecordNotSaved) { david.save! }
-    assert_equal exc.record, david
+    assert_equal david, exc.record
 
     david = DeveloperWithCanceledCallbacks.find(1)
     david.salary = 10_000_000
@@ -554,7 +554,7 @@ class CallbacksTest < ActiveRecord::TestCase
     david = DeveloperWithCanceledCallbacks.find(1)
     assert !david.destroy
     exc = assert_raise(ActiveRecord::RecordNotDestroyed) { david.destroy! }
-    assert_equal exc.record, david
+    assert_equal david, exc.record
     assert_not_nil ImmutableDeveloper.find_by_id(1)
 
     someone = CallbackHaltedDeveloper.find(1)
diff --git a/activerecord/test/cases/comment_test.rb b/activerecord/test/cases/comment_test.rb
index 262ad319be..a625299e8d 100644
--- a/activerecord/test/cases/comment_test.rb
+++ b/activerecord/test/cases/comment_test.rb
@@ -2,7 +2,6 @@ require "cases/helper"
 require "support/schema_dumping_helper"
 
 if ActiveRecord::Base.connection.supports_comments?
-
   class CommentTest < ActiveRecord::TestCase
     include SchemaDumpingHelper
 
@@ -102,6 +101,7 @@ if ActiveRecord::Base.connection.supports_comments?
       # Do all the stuff from other tests
       @connection.add_column    :commenteds, :rating, :integer, comment: "I am running out of imagination"
       @connection.change_column :commenteds, :content, :string, comment: "Whoa, content describes itself!"
+      @connection.change_column :commenteds, :content, :string
       @connection.change_column :commenteds, :obvious, :string, comment: nil
       @connection.add_index     :commenteds, :obvious, name: "idx_obvious", comment: "We need to see obvious comments"
 
@@ -135,5 +135,4 @@ if ActiveRecord::Base.connection.supports_comments?
       assert_no_match %r[t\.string\s+"absent_comment", comment:\n], output
     end
   end
-
 end
diff --git a/activerecord/test/cases/connection_adapters/merge_and_resolve_default_url_config_test.rb b/activerecord/test/cases/connection_adapters/merge_and_resolve_default_url_config_test.rb
index a8955152c3..8faa67255d 100644
--- a/activerecord/test/cases/connection_adapters/merge_and_resolve_default_url_config_test.rb
+++ b/activerecord/test/cases/connection_adapters/merge_and_resolve_default_url_config_test.rb
@@ -142,13 +142,13 @@ module ActiveRecord
                      "database" => "foo",
                      "host"     => "localhost" }
         assert_equal expected, actual["default_env"]
-        assert_equal nil,      actual["production"]
-        assert_equal nil,      actual["development"]
-        assert_equal nil,      actual["test"]
-        assert_equal nil,      actual[:default_env]
-        assert_equal nil,      actual[:production]
-        assert_equal nil,      actual[:development]
-        assert_equal nil,      actual[:test]
+        assert_nil actual["production"]
+        assert_nil actual["development"]
+        assert_nil actual["test"]
+        assert_nil actual[:default_env]
+        assert_nil actual[:production]
+        assert_nil actual[:development]
+        assert_nil actual[:test]
       end
 
       def test_blank_with_database_url_with_rails_env
@@ -162,15 +162,15 @@ module ActiveRecord
                      "host"     => "localhost" }
 
         assert_equal expected, actual["not_production"]
-        assert_equal nil,      actual["production"]
-        assert_equal nil,      actual["default_env"]
-        assert_equal nil,      actual["development"]
-        assert_equal nil,      actual["test"]
-        assert_equal nil,      actual[:default_env]
-        assert_equal nil,      actual[:not_production]
-        assert_equal nil,      actual[:production]
-        assert_equal nil,      actual[:development]
-        assert_equal nil,      actual[:test]
+        assert_nil actual["production"]
+        assert_nil actual["default_env"]
+        assert_nil actual["development"]
+        assert_nil actual["test"]
+        assert_nil actual[:default_env]
+        assert_nil actual[:not_production]
+        assert_nil actual[:production]
+        assert_nil actual[:development]
+        assert_nil actual[:test]
       end
 
       def test_blank_with_database_url_with_rack_env
@@ -184,15 +184,15 @@ module ActiveRecord
                      "host"     => "localhost" }
 
         assert_equal expected, actual["not_production"]
-        assert_equal nil,      actual["production"]
-        assert_equal nil,      actual["default_env"]
-        assert_equal nil,      actual["development"]
-        assert_equal nil,      actual["test"]
-        assert_equal nil,      actual[:default_env]
-        assert_equal nil,      actual[:not_production]
-        assert_equal nil,      actual[:production]
-        assert_equal nil,      actual[:development]
-        assert_equal nil,      actual[:test]
+        assert_nil actual["production"]
+        assert_nil actual["default_env"]
+        assert_nil actual["development"]
+        assert_nil actual["test"]
+        assert_nil actual[:default_env]
+        assert_nil actual[:not_production]
+        assert_nil actual[:production]
+        assert_nil actual[:development]
+        assert_nil actual[:test]
       end
 
       def test_database_url_with_ipv6_host_and_port
diff --git a/activerecord/test/cases/connection_adapters/schema_cache_test.rb b/activerecord/test/cases/connection_adapters/schema_cache_test.rb
index d4459603af..1b4f80fc67 100644
--- a/activerecord/test/cases/connection_adapters/schema_cache_test.rb
+++ b/activerecord/test/cases/connection_adapters/schema_cache_test.rb
@@ -12,6 +12,33 @@ module ActiveRecord
         assert_equal "id", @cache.primary_keys("posts")
       end
 
+      def test_yaml_dump_and_load
+        @cache.columns("posts")
+        @cache.columns_hash("posts")
+        @cache.data_sources("posts")
+        @cache.primary_keys("posts")
+
+        new_cache = YAML.load(YAML.dump(@cache))
+        assert_no_queries do
+          assert_equal 11, new_cache.columns("posts").size
+          assert_equal 11, new_cache.columns_hash("posts").size
+          assert new_cache.data_sources("posts")
+          assert_equal "id", new_cache.primary_keys("posts")
+        end
+      end
+
+      def test_yaml_loads_5_1_dump
+        body = File.open(schema_dump_path).read
+        cache = YAML.load(body)
+
+        assert_no_queries do
+          assert_equal 11, cache.columns("posts").size
+          assert_equal 11, cache.columns_hash("posts").size
+          assert cache.data_sources("posts")
+          assert_equal "id", cache.primary_keys("posts")
+        end
+      end
+
       def test_primary_key_for_non_existent_table
         assert_nil @cache.primary_keys("omgponies")
       end
@@ -45,10 +72,12 @@ module ActiveRecord
 
         @cache = Marshal.load(Marshal.dump(@cache))
 
-        assert_equal 11, @cache.columns("posts").size
-        assert_equal 11, @cache.columns_hash("posts").size
-        assert @cache.data_sources("posts")
-        assert_equal "id", @cache.primary_keys("posts")
+        assert_no_queries do
+          assert_equal 11, @cache.columns("posts").size
+          assert_equal 11, @cache.columns_hash("posts").size
+          assert @cache.data_sources("posts")
+          assert_equal "id", @cache.primary_keys("posts")
+        end
       end
 
       def test_table_methods_deprecation
@@ -56,6 +85,12 @@ module ActiveRecord
         assert_deprecated { assert @cache.tables("posts") }
         assert_deprecated { @cache.clear_table_cache!("posts") }
       end
+
+      private
+
+        def schema_dump_path
+          "test/assets/schema_dump_5_1.yml"
+        end
     end
   end
 end
diff --git a/activerecord/test/cases/connection_pool_test.rb b/activerecord/test/cases/connection_pool_test.rb
index 1d4cd3c78b..42600e53fd 100644
--- a/activerecord/test/cases/connection_pool_test.rb
+++ b/activerecord/test/cases/connection_pool_test.rb
@@ -501,11 +501,11 @@ module ActiveRecord
                 first_thread.join(2)
                 second_thread.join(2)
 
-                puts '---'
+                puts "---"
                 p [first_thread, second_thread]
                 p pool.stat
                 p pool.connections.map(&:owner)
-                puts '<<<'
+                puts "<<<"
                 puts
               end
 
diff --git a/activerecord/test/cases/defaults_test.rb b/activerecord/test/cases/defaults_test.rb
index fcaff38f82..6532efcf22 100644
--- a/activerecord/test/cases/defaults_test.rb
+++ b/activerecord/test/cases/defaults_test.rb
@@ -169,7 +169,7 @@ if current_adapter?(:Mysql2Adapter)
           assert_nil record.non_null_text
           assert_nil record.non_null_blob
 
-          assert_raises(ActiveRecord::StatementInvalid) { klass.create }
+          assert_raises(ActiveRecord::NotNullViolation) { klass.create }
         end
       end
     end
diff --git a/activerecord/test/cases/finder_test.rb b/activerecord/test/cases/finder_test.rb
index 7eaf31aa24..d6d24004fe 100644
--- a/activerecord/test/cases/finder_test.rb
+++ b/activerecord/test/cases/finder_test.rb
@@ -488,12 +488,12 @@ class FinderTest < ActiveRecord::TestCase
     assert_equal topics(:fourth), Topic.offset(1).second_to_last
     assert_equal topics(:fourth), Topic.offset(2).second_to_last
     assert_equal topics(:fourth), Topic.offset(3).second_to_last
-    assert_equal nil, Topic.offset(4).second_to_last
-    assert_equal nil, Topic.offset(5).second_to_last
+    assert_nil Topic.offset(4).second_to_last
+    assert_nil Topic.offset(5).second_to_last
 
     #test with limit
-    # assert_equal nil, Topic.limit(1).second # TODO: currently failing
-    assert_equal nil, Topic.limit(1).second_to_last
+    # assert_nil Topic.limit(1).second # TODO: currently failing
+    assert_nil Topic.limit(1).second_to_last
   end
 
   def test_second_to_last_have_primary_key_order_by_default
@@ -516,15 +516,15 @@ class FinderTest < ActiveRecord::TestCase
     # test with offset
     assert_equal topics(:third), Topic.offset(1).third_to_last
     assert_equal topics(:third), Topic.offset(2).third_to_last
-    assert_equal nil, Topic.offset(3).third_to_last
-    assert_equal nil, Topic.offset(4).third_to_last
-    assert_equal nil, Topic.offset(5).third_to_last
+    assert_nil Topic.offset(3).third_to_last
+    assert_nil Topic.offset(4).third_to_last
+    assert_nil Topic.offset(5).third_to_last
 
     # test with limit
-    # assert_equal nil, Topic.limit(1).third # TODO: currently failing
-    assert_equal nil, Topic.limit(1).third_to_last
-    # assert_equal nil, Topic.limit(2).third # TODO: currently failing
-    assert_equal nil, Topic.limit(2).third_to_last
+    # assert_nil Topic.limit(1).third # TODO: currently failing
+    assert_nil Topic.limit(1).third_to_last
+    # assert_nil Topic.limit(2).third # TODO: currently failing
+    assert_nil Topic.limit(2).third_to_last
   end
 
   def test_third_to_last_have_primary_key_order_by_default
@@ -983,7 +983,6 @@ class FinderTest < ActiveRecord::TestCase
 
     assert_equal devs[2], Developer.offset(2).first
     assert_equal devs[-3], Developer.offset(2).last
-    assert_equal devs[-3], Developer.offset(2).last
     assert_equal devs[-3], Developer.offset(2).order("id DESC").first
   end
 
@@ -1167,7 +1166,7 @@ class FinderTest < ActiveRecord::TestCase
   end
 
   test "find_by returns nil if the record is missing" do
-    assert_equal nil, Post.find_by("1 = 0")
+    assert_nil Post.find_by("1 = 0")
   end
 
   test "find_by with associations" do
@@ -1221,7 +1220,7 @@ class FinderTest < ActiveRecord::TestCase
     assert_equal tyre2, zyke.tyres.custom_find_by(id: tyre2.id)
   end
 
-  protected
+  private
     def table_with_custom_primary_key
       yield(Class.new(Toy) do
         def self.name
diff --git a/activerecord/test/cases/fixtures_test.rb b/activerecord/test/cases/fixtures_test.rb
index f3d0e4a1b1..dd48053823 100644
--- a/activerecord/test/cases/fixtures_test.rb
+++ b/activerecord/test/cases/fixtures_test.rb
@@ -12,9 +12,11 @@ require "models/company"
 require "models/computer"
 require "models/course"
 require "models/developer"
+require "models/dog"
 require "models/doubloon"
 require "models/joke"
 require "models/matey"
+require "models/other_dog"
 require "models/parrot"
 require "models/pirate"
 require "models/post"
@@ -211,9 +213,19 @@ class FixturesTest < ActiveRecord::TestCase
   end
 
   def test_dirty_dirty_yaml_file
-    assert_raise(ActiveRecord::Fixture::FormatError) do
-      ActiveRecord::FixtureSet.new(Account.connection, "courses", Course, FIXTURES_ROOT + "/naked/yml/courses")
+    fixture_path = FIXTURES_ROOT + "/naked/yml/courses"
+    error = assert_raise(ActiveRecord::Fixture::FormatError) do
+      ActiveRecord::FixtureSet.new(Account.connection, "courses", Course, fixture_path)
     end
+    assert_equal "fixture is not a hash: #{fixture_path}.yml", error.to_s
+  end
+
+  def test_yaml_file_with_one_invalid_fixture
+    fixture_path = FIXTURES_ROOT + "/naked/yml/courses_with_invalid_key"
+    error = assert_raise(ActiveRecord::Fixture::FormatError) do
+      ActiveRecord::FixtureSet.new(Account.connection, "courses", Course, fixture_path)
+    end
+    assert_equal "fixture key is not a hash: #{fixture_path}.yml, keys: [\"two\"]", error.to_s
   end
 
   def test_yaml_file_with_invalid_column
@@ -1011,3 +1023,16 @@ class FixtureClassNamesTest < ActiveRecord::TestCase
     assert_nil fixture_class_names["unregistered_identifier"]
   end
 end
+
+class SameNameDifferentDatabaseFixturesTest < ActiveRecord::TestCase
+  fixtures :dogs, :other_dogs
+
+  test "fixtures are properly loaded" do
+    # Force loading the fixtures again to reproduce issue
+    ActiveRecord::FixtureSet.reset_cache
+    create_fixtures("dogs", "other_dogs")
+
+    assert_kind_of Dog, dogs(:sophie)
+    assert_kind_of OtherDog, other_dogs(:lassie)
+  end
+end
diff --git a/activerecord/test/cases/integration_test.rb b/activerecord/test/cases/integration_test.rb
index 00457965d7..d7aa091623 100644
--- a/activerecord/test/cases/integration_test.rb
+++ b/activerecord/test/cases/integration_test.rb
@@ -15,7 +15,7 @@ class IntegrationTest < ActiveRecord::TestCase
 
   def test_to_param_returns_nil_if_not_persisted
     client = Client.new
-    assert_equal nil, client.to_param
+    assert_nil client.to_param
   end
 
   def test_to_param_returns_id_if_not_persisted_but_id_is_set
@@ -89,7 +89,7 @@ class IntegrationTest < ActiveRecord::TestCase
 
   def test_to_param_class_method_uses_default_if_not_persisted
     firm = Firm.new(name: "Fancy Shirts")
-    assert_equal nil, firm.to_param
+    assert_nil firm.to_param
   end
 
   def test_to_param_with_no_arguments
diff --git a/activerecord/test/cases/json_serialization_test.rb b/activerecord/test/cases/json_serialization_test.rb
index a2150483f3..155e858822 100644
--- a/activerecord/test/cases/json_serialization_test.rb
+++ b/activerecord/test/cases/json_serialization_test.rb
@@ -243,7 +243,7 @@ class DatabaseConnectedJsonEncodingTest < ActiveRecord::TestCase
 
     assert !@david.posts.first.respond_to?(:favorite_quote)
     assert_match %r{"favorite_quote":"Constraints are liberating"}, json
-    assert_equal %r{"favorite_quote":}.match(json).size, 1
+    assert_equal 1, %r{"favorite_quote":}.match(json).size
   end
 
   def test_should_allow_only_option_for_list_of_authors
diff --git a/activerecord/test/cases/locking_test.rb b/activerecord/test/cases/locking_test.rb
index 9b0ec54aa7..95fb670dac 100644
--- a/activerecord/test/cases/locking_test.rb
+++ b/activerecord/test/cases/locking_test.rb
@@ -579,7 +579,7 @@ unless in_memory_db?
         assert first.end > second.end
       end
 
-      protected
+      private
 
       def duel(zzz = 5)
         t0, t1, t2, t3 = nil, nil, nil, nil
diff --git a/activerecord/test/cases/migration/change_schema_test.rb b/activerecord/test/cases/migration/change_schema_test.rb
index bdb90eaa74..03f9c4a9ed 100644
--- a/activerecord/test/cases/migration/change_schema_test.rb
+++ b/activerecord/test/cases/migration/change_schema_test.rb
@@ -43,7 +43,7 @@ module ActiveRecord
           t.column :foo, :string, null: false
         end
 
-        assert_raises(ActiveRecord::StatementInvalid) do
+        assert_raises(ActiveRecord::NotNullViolation) do
           connection.execute "insert into testings (foo) values (NULL)"
         end
       end
@@ -233,7 +233,7 @@ module ActiveRecord
           end
           connection.add_column :testings, :bar, :string, null: false
 
-          assert_raise(ActiveRecord::StatementInvalid) do
+          assert_raise(ActiveRecord::NotNullViolation) do
             connection.execute "insert into testings (foo, bar) values ('hello', NULL)"
           end
         end
@@ -244,12 +244,16 @@ module ActiveRecord
           t.column :foo, :string
         end
 
-        con = connection
-        connection.execute "insert into testings (#{con.quote_column_name('id')}, #{con.quote_column_name('foo')}) values (1, 'hello')"
-        assert_nothing_raised { connection.add_column :testings, :bar, :string, null: false, default: "default" }
+        quoted_id  = connection.quote_column_name("id")
+        quoted_foo = connection.quote_column_name("foo")
+        quoted_bar = connection.quote_column_name("bar")
+        connection.execute("insert into testings (#{quoted_id}, #{quoted_foo}) values (1, 'hello')")
+        assert_nothing_raised do
+          connection.add_column :testings, :bar, :string, null: false, default: "default"
+        end
 
-        assert_raises(ActiveRecord::StatementInvalid) do
-          connection.execute "insert into testings (#{con.quote_column_name('id')}, #{con.quote_column_name('foo')}, #{con.quote_column_name('bar')}) values (2, 'hello', NULL)"
+        assert_raises(ActiveRecord::NotNullViolation) do
+          connection.execute("insert into testings (#{quoted_id}, #{quoted_foo}, #{quoted_bar}) values (2, 'hello', NULL)")
         end
       end
 
diff --git a/activerecord/test/cases/migration/change_table_test.rb b/activerecord/test/cases/migration/change_table_test.rb
index ec817a579b..8a4242cf1d 100644
--- a/activerecord/test/cases/migration/change_table_test.rb
+++ b/activerecord/test/cases/migration/change_table_test.rb
@@ -101,7 +101,12 @@ module ActiveRecord
 
       def test_primary_key_creates_primary_key_column
         with_change_table do |t|
-          @connection.expect :add_column, nil, [:delete_me, :id, :primary_key, primary_key: true, first: true]
+          if current_adapter?(:Mysql2Adapter)
+            @connection.expect :add_column, nil, [:delete_me, :id, :primary_key, { first: true, auto_increment: true, limit: 8, primary_key: true }]
+          else
+            @connection.expect :add_column, nil, [:delete_me, :id, :primary_key, primary_key: true, first: true]
+          end
+
           t.primary_key :id, first: true
         end
       end
diff --git a/activerecord/test/cases/migration/foreign_key_test.rb b/activerecord/test/cases/migration/foreign_key_test.rb
index cab2069754..9be6667aa1 100644
--- a/activerecord/test/cases/migration/foreign_key_test.rb
+++ b/activerecord/test/cases/migration/foreign_key_test.rb
@@ -76,7 +76,7 @@ if ActiveRecord::Base.connection.supports_foreign_keys?
         end
 
         def test_add_foreign_key_with_non_standard_primary_key
-          with_example_table @connection, "space_shuttles", "pk integer PRIMARY KEY" do
+          with_example_table @connection, "space_shuttles", "pk BIGINT PRIMARY KEY" do
             @connection.add_foreign_key(:astronauts, :space_shuttles,
                                         column: "rocket_id", primary_key: "pk", name: "custom_pk")
 
@@ -101,7 +101,7 @@ if ActiveRecord::Base.connection.supports_foreign_keys?
           fk = foreign_keys.first
           if current_adapter?(:Mysql2Adapter)
             # ON DELETE RESTRICT is the default on MySQL
-            assert_equal nil, fk.on_delete
+            assert_nil fk.on_delete
           else
             assert_equal :restrict, fk.on_delete
           end
@@ -229,7 +229,7 @@ if ActiveRecord::Base.connection.supports_foreign_keys?
             create_table("cities") { |t| }
 
             create_table("houses") do |t|
-              t.column :city_id, :integer
+              t.column :city_id, :bigint
             end
             add_foreign_key :houses, :cities, column: "city_id"
 
@@ -261,7 +261,7 @@ if ActiveRecord::Base.connection.supports_foreign_keys?
             create_table(:schools)
 
             create_table(:classes) do |t|
-              t.column :school_id, :integer
+              t.column :school_id, :bigint
             end
             add_foreign_key :classes, :schools
           end
diff --git a/activerecord/test/cases/migration/references_foreign_key_test.rb b/activerecord/test/cases/migration/references_foreign_key_test.rb
index 528811db49..4957ab8b3d 100644
--- a/activerecord/test/cases/migration/references_foreign_key_test.rb
+++ b/activerecord/test/cases/migration/references_foreign_key_test.rb
@@ -42,7 +42,7 @@ if ActiveRecord::Base.connection.supports_foreign_keys?
 
         test "options hash can be passed" do
           @connection.change_table :testing_parents do |t|
-            t.integer :other_id
+            t.bigint :other_id
             t.index :other_id, unique: true
           end
           @connection.create_table :testings do |t|
@@ -92,7 +92,7 @@ if ActiveRecord::Base.connection.supports_foreign_keys?
 
         test "foreign keys accept options when changing the table" do
           @connection.change_table :testing_parents do |t|
-            t.integer :other_id
+            t.bigint :other_id
             t.index :other_id, unique: true
           end
           @connection.create_table :testings
@@ -177,8 +177,8 @@ if ActiveRecord::Base.connection.supports_foreign_keys?
 
         test "multiple foreign keys can be added to the same table" do
           @connection.create_table :testings do |t|
-            t.integer :col_1
-            t.integer :col_2
+            t.bigint :col_1
+            t.bigint :col_2
 
             t.foreign_key :testing_parents, column: :col_1
             t.foreign_key :testing_parents, column: :col_2
diff --git a/activerecord/test/cases/migration_test.rb b/activerecord/test/cases/migration_test.rb
index 22484ad678..082cfd3242 100644
--- a/activerecord/test/cases/migration_test.rb
+++ b/activerecord/test/cases/migration_test.rb
@@ -705,7 +705,7 @@ class MigrationTest < ActiveRecord::TestCase
     end
   end
 
-  protected
+  private
     # This is needed to isolate class_attribute assignments like `table_name_prefix`
     # for each test case.
     def new_isolated_reminder_class
diff --git a/activerecord/test/cases/primary_keys_test.rb b/activerecord/test/cases/primary_keys_test.rb
index eaaf50d14f..1d72899102 100644
--- a/activerecord/test/cases/primary_keys_test.rb
+++ b/activerecord/test/cases/primary_keys_test.rb
@@ -129,12 +129,6 @@ class PrimaryKeysTest < ActiveRecord::TestCase
     assert_nothing_raised { MixedCaseMonkey.find(1).destroy }
   end
 
-  def test_supports_primary_key
-    assert_nothing_raised do
-      ActiveRecord::Base.connection.supports_primary_key?
-    end
-  end
-
   if ActiveRecord::Base.connection.supports_primary_key?
     def test_primary_key_returns_value_if_it_exists
       klass = Class.new(ActiveRecord::Base) do
@@ -216,6 +210,43 @@ class PrimaryKeyWithNoConnectionTest < ActiveRecord::TestCase
   end
 end
 
+class PrimaryKeyWithAutoIncrementTest < ActiveRecord::TestCase
+  self.use_transactional_tests = false
+
+  class AutoIncrement < ActiveRecord::Base
+  end
+
+  def setup
+    @connection = ActiveRecord::Base.connection
+  end
+
+  def teardown
+    @connection.drop_table(:auto_increments, if_exists: true)
+  end
+
+  def test_primary_key_with_auto_increment
+    @connection.create_table(:auto_increments, id: :integer, auto_increment: true, force: true)
+    assert_auto_incremented
+  end
+
+  def test_primary_key_with_auto_increment_and_bigint
+    @connection.create_table(:auto_increments, id: :bigint, auto_increment: true, force: true)
+    assert_auto_incremented
+  end
+
+  private
+    def assert_auto_incremented
+      record1 = AutoIncrement.create!
+      assert_not_nil record1.id
+
+      record1.destroy
+
+      record2 = AutoIncrement.create!
+      assert_not_nil record2.id
+      assert_operator record2.id, :>, record1.id
+    end
+end
+
 class PrimaryKeyAnyTypeTest < ActiveRecord::TestCase
   include SchemaDumpingHelper
 
@@ -289,85 +320,69 @@ class CompositePrimaryKeyTest < ActiveRecord::TestCase
 end
 
 if current_adapter?(:Mysql2Adapter)
-  class PrimaryKeyBigintNilDefaultTest < ActiveRecord::TestCase
+  class PrimaryKeyIntegerNilDefaultTest < ActiveRecord::TestCase
     include SchemaDumpingHelper
 
     self.use_transactional_tests = false
 
     def setup
       @connection = ActiveRecord::Base.connection
-      @connection.create_table(:bigint_defaults, id: :bigint, default: nil, force: true)
+      @connection.create_table(:int_defaults, id: :integer, default: nil, force: true)
     end
 
     def teardown
-      @connection.drop_table :bigint_defaults, if_exists: true
+      @connection.drop_table :int_defaults, if_exists: true
     end
 
-    test "primary key with bigint allows default override via nil" do
-      column = @connection.columns(:bigint_defaults).find { |c| c.name == "id" }
-      assert column.bigint?
+    test "primary key with integer allows default override via nil" do
+      column = @connection.columns(:int_defaults).find { |c| c.name == "id" }
+      assert_equal :integer, column.type
       assert_not column.auto_increment?
     end
 
-    test "schema dump primary key with bigint default nil" do
-      schema = dump_table_schema "bigint_defaults"
-      assert_match %r{create_table "bigint_defaults", id: :bigint, default: nil}, schema
+    test "schema dump primary key with int default nil" do
+      schema = dump_table_schema "int_defaults"
+      assert_match %r{create_table "int_defaults", id: :integer, default: nil}, schema
     end
   end
 end
 
-if current_adapter?(:PostgreSQLAdapter, :Mysql2Adapter)
-  class PrimaryKeyBigSerialTest < ActiveRecord::TestCase
-    include SchemaDumpingHelper
+class PrimaryKeyIntegerTest < ActiveRecord::TestCase
+  include SchemaDumpingHelper
 
-    self.use_transactional_tests = false
+  self.use_transactional_tests = false
 
-    class Widget < ActiveRecord::Base
-    end
+  class Widget < ActiveRecord::Base
+  end
 
-    setup do
-      @connection = ActiveRecord::Base.connection
-      if current_adapter?(:PostgreSQLAdapter)
-        @connection.create_table(:widgets, id: :bigserial, force: true)
-      else
-        @connection.create_table(:widgets, id: :bigint, force: true)
-      end
-    end
+  setup do
+    @connection = ActiveRecord::Base.connection
+    @connection.create_table(:widgets, force: true)
+  end
 
-    teardown do
-      @connection.drop_table :widgets, if_exists: true
-      Widget.reset_column_information
-    end
+  teardown do
+    @connection.drop_table :widgets, if_exists: true
+    Widget.reset_column_information
+  end
 
-    test "primary key column type with bigserial" do
-      column_type = Widget.type_for_attribute(Widget.primary_key)
-      assert_equal :integer, column_type.type
-      assert_equal 8, column_type.limit
+  if current_adapter?(:PostgreSQLAdapter, :Mysql2Adapter)
+    test "schema dump primary key with bigserial" do
+      schema = dump_table_schema "widgets"
+      assert_match %r{create_table "widgets", force: :cascade}, schema
     end
+  end
 
-    test "primary key with bigserial are automatically numbered" do
-      widget = Widget.create!
-      assert_not_nil widget.id
-    end
+  test "primary key column type" do
+    column_type = Widget.type_for_attribute(Widget.primary_key)
+    assert_equal :integer, column_type.type
 
-    test "schema dump primary key with bigserial" do
-      schema = dump_table_schema "widgets"
-      if current_adapter?(:PostgreSQLAdapter)
-        assert_match %r{create_table "widgets", id: :bigserial, force: :cascade}, schema
-      else
-        assert_match %r{create_table "widgets", id: :bigint, force: :cascade}, schema
-      end
+    if current_adapter?(:PostgreSQLAdapter, :Mysql2Adapter)
+      assert_equal 8, column_type.limit
     end
 
     if current_adapter?(:Mysql2Adapter)
-      test "primary key column type with options" do
-        @connection.create_table(:widgets, id: :primary_key, limit: 8, unsigned: true, force: true)
-        column = @connection.columns(:widgets).find { |c| c.name == "id" }
-        assert column.auto_increment?
-        assert_equal :integer, column.type
-        assert_equal 8, column.limit
-        assert column.unsigned?
-      end
+      column = @connection.columns(:widgets).find { |c| c.name == "id" }
+      assert column.auto_increment?
     end
   end
 end
diff --git a/activerecord/test/cases/query_cache_test.rb b/activerecord/test/cases/query_cache_test.rb
index 90054ce83d..4a49bfe9b1 100644
--- a/activerecord/test/cases/query_cache_test.rb
+++ b/activerecord/test/cases/query_cache_test.rb
@@ -202,6 +202,20 @@ class QueryCacheTest < ActiveRecord::TestCase
     ActiveSupport::Notifications.unsubscribe subscriber
   end
 
+  def test_query_cache_does_not_allow_sql_key_mutation
+    subscriber = ActiveSupport::Notifications.subscribe("sql.active_record") do |_, _, _, _, payload|
+      payload[:sql].downcase!
+    end
+
+    assert_raises RuntimeError do
+      ActiveRecord::Base.cache do
+        assert_queries(1) { Task.find(1); Task.find(1) }
+      end
+    end
+  ensure
+    ActiveSupport::Notifications.unsubscribe subscriber
+  end
+
   def test_cache_is_flat
     Task.cache do
       assert_queries(1) { Topic.find(1); Topic.find(1); }
diff --git a/activerecord/test/cases/reflection_test.rb b/activerecord/test/cases/reflection_test.rb
index 5dac3d064b..a90058e8bb 100644
--- a/activerecord/test/cases/reflection_test.rb
+++ b/activerecord/test/cases/reflection_test.rb
@@ -86,8 +86,8 @@ class ReflectionTest < ActiveRecord::TestCase
     column = @first.column_for_attribute("attribute_that_doesnt_exist")
     assert_instance_of ActiveRecord::ConnectionAdapters::NullColumn, column
     assert_equal "attribute_that_doesnt_exist", column.name
-    assert_equal nil, column.sql_type
-    assert_equal nil, column.type
+    assert_nil column.sql_type
+    assert_nil column.type
   end
 
   def test_non_existent_types_are_identity_types
diff --git a/activerecord/test/cases/relation/or_test.rb b/activerecord/test/cases/relation/or_test.rb
index 2796595523..abb7ca72dd 100644
--- a/activerecord/test/cases/relation/or_test.rb
+++ b/activerecord/test/cases/relation/or_test.rb
@@ -79,7 +79,7 @@ module ActiveRecord
       expected = Post.where("id = 1 or id = 2").to_a
       p = Post.where("id = 1")
       p.load
-      assert_equal p.loaded?, true
+      assert_equal true, p.loaded?
       assert_equal expected, p.or(Post.where("id = 2")).to_a
     end
 
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 96833ad428..981c2d758d 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -442,7 +442,7 @@ class RelationTest < ActiveRecord::TestCase
     assert_no_queries(ignore_none: false) do
       assert_equal 0, Developer.none.count
       assert_equal 0, Developer.none.calculate(:count, nil)
-      assert_equal nil, Developer.none.calculate(:average, "salary")
+      assert_nil Developer.none.calculate(:average, "salary")
     end
   end
 
@@ -485,28 +485,28 @@ class RelationTest < ActiveRecord::TestCase
   def test_null_relation_average
     ac = Aircraft.new
     assert_equal Hash.new, ac.engines.group(:car_id).average(:id)
-    assert_equal nil, ac.engines.average(:id)
+    assert_nil ac.engines.average(:id)
     ac.save
     assert_equal Hash.new, ac.engines.group(:car_id).average(:id)
-    assert_equal nil, ac.engines.average(:id)
+    assert_nil ac.engines.average(:id)
   end
 
   def test_null_relation_minimum
     ac = Aircraft.new
     assert_equal Hash.new, ac.engines.group(:car_id).minimum(:id)
-    assert_equal nil, ac.engines.minimum(:id)
+    assert_nil ac.engines.minimum(:id)
     ac.save
     assert_equal Hash.new, ac.engines.group(:car_id).minimum(:id)
-    assert_equal nil, ac.engines.minimum(:id)
+    assert_nil ac.engines.minimum(:id)
   end
 
   def test_null_relation_maximum
     ac = Aircraft.new
     assert_equal Hash.new, ac.engines.group(:car_id).maximum(:id)
-    assert_equal nil, ac.engines.maximum(:id)
+    assert_nil ac.engines.maximum(:id)
     ac.save
     assert_equal Hash.new, ac.engines.group(:car_id).maximum(:id)
-    assert_equal nil, ac.engines.maximum(:id)
+    assert_nil ac.engines.maximum(:id)
   end
 
   def test_null_relation_in_where_condition
@@ -1814,7 +1814,7 @@ class RelationTest < ActiveRecord::TestCase
   end
 
   test "find_by returns nil if the record is missing" do
-    assert_equal nil, Post.all.find_by("1 = 0")
+    assert_nil Post.all.find_by("1 = 0")
   end
 
   test "find_by doesn't have implicit ordering" do
diff --git a/activerecord/test/cases/schema_dumper_test.rb b/activerecord/test/cases/schema_dumper_test.rb
index 007f976f2e..bea78d2a95 100644
--- a/activerecord/test/cases/schema_dumper_test.rb
+++ b/activerecord/test/cases/schema_dumper_test.rb
@@ -148,12 +148,7 @@ class SchemaDumperTest < ActiveRecord::TestCase
       assert_match %r{c_int_4.*limit: 4}, output
     end
 
-    if current_adapter?(:SQLite3Adapter)
-      assert_match %r{c_int_5.*limit: 5}, output
-      assert_match %r{c_int_6.*limit: 6}, output
-      assert_match %r{c_int_7.*limit: 7}, output
-      assert_match %r{c_int_8.*limit: 8}, output
-    elsif current_adapter?(:OracleAdapter)
+    if current_adapter?(:SQLite3Adapter, :OracleAdapter)
       assert_match %r{c_int_5.*limit: 5}, output
       assert_match %r{c_int_6.*limit: 6}, output
       assert_match %r{c_int_7.*limit: 7}, output
@@ -346,7 +341,7 @@ class SchemaDumperTest < ActiveRecord::TestCase
 
       create_table("dogs") do |t|
         t.column :name, :string
-        t.column :owner_id, :integer
+        t.column :owner_id, :bigint
         t.index [:name]
         t.foreign_key :dog_owners, column: "owner_id" if supports_foreign_keys?
       end
diff --git a/activerecord/test/cases/scoping/default_scoping_test.rb b/activerecord/test/cases/scoping/default_scoping_test.rb
index b3dc979720..b408a6000b 100644
--- a/activerecord/test/cases/scoping/default_scoping_test.rb
+++ b/activerecord/test/cases/scoping/default_scoping_test.rb
@@ -50,7 +50,7 @@ class DefaultScopingTest < ActiveRecord::TestCase
 
   def test_default_scope_with_conditions_string
     assert_equal Developer.where(name: "David").map(&:id).sort, DeveloperCalledDavid.all.map(&:id).sort
-    assert_equal nil, DeveloperCalledDavid.create!.name
+    assert_nil DeveloperCalledDavid.create!.name
   end
 
   def test_default_scope_with_conditions_hash
@@ -314,7 +314,7 @@ class DefaultScopingTest < ActiveRecord::TestCase
   end
 
   def test_create_attribute_overwrites_default_values
-    assert_equal nil, PoorDeveloperCalledJamis.create!(salary: nil).salary
+    assert_nil PoorDeveloperCalledJamis.create!(salary: nil).salary
     assert_equal 50000, PoorDeveloperCalledJamis.create!(name: "David").salary
   end
 
diff --git a/activerecord/test/cases/scoping/relation_scoping_test.rb b/activerecord/test/cases/scoping/relation_scoping_test.rb
index 47310a151e..a1ae57fdbb 100644
--- a/activerecord/test/cases/scoping/relation_scoping_test.rb
+++ b/activerecord/test/cases/scoping/relation_scoping_test.rb
@@ -277,7 +277,7 @@ class NestedRelationScopingTest < ActiveRecord::TestCase
         assert_equal "David", Developer.first.name
 
         Developer.unscoped.where("name = 'Maiha'") do
-          assert_equal nil, Developer.first
+          assert_nil Developer.first
         end
 
         # ensure that scoping is restored
diff --git a/activerecord/test/cases/secure_token_test.rb b/activerecord/test/cases/secure_token_test.rb
index eda0229c26..7b9cbee40a 100644
--- a/activerecord/test/cases/secure_token_test.rb
+++ b/activerecord/test/cases/secure_token_test.rb
@@ -27,6 +27,6 @@ class SecureTokenTest < ActiveRecord::TestCase
     @user.token = "custom-secure-token"
     @user.save
 
-    assert_equal @user.token, "custom-secure-token"
+    assert_equal "custom-secure-token", @user.token
   end
 end
diff --git a/activerecord/test/cases/serialized_attribute_test.rb b/activerecord/test/cases/serialized_attribute_test.rb
index 1ccbf3ed4a..a469da0a5b 100644
--- a/activerecord/test/cases/serialized_attribute_test.rb
+++ b/activerecord/test/cases/serialized_attribute_test.rb
@@ -185,14 +185,14 @@ class SerializedAttributeTest < ActiveRecord::TestCase
     topic = Topic.new(content: true)
     assert topic.save
     topic = topic.reload
-    assert_equal topic.content, true
+    assert_equal true, topic.content
   end
 
   def test_serialized_boolean_value_false
     topic = Topic.new(content: false)
     assert topic.save
     topic = topic.reload
-    assert_equal topic.content, false
+    assert_equal false, topic.content
   end
 
   def test_serialize_with_coder
@@ -211,7 +211,7 @@ class SerializedAttributeTest < ActiveRecord::TestCase
     topic.save!
     topic.reload
     assert_kind_of some_class, topic.content
-    assert_equal topic.content, some_class.new("my value")
+    assert_equal some_class.new("my value"), topic.content
   end
 
   def test_serialize_attribute_via_select_method_when_time_zone_available
diff --git a/activerecord/test/cases/tasks/mysql_rake_test.rb b/activerecord/test/cases/tasks/mysql_rake_test.rb
index dbe935808e..285e718596 100644
--- a/activerecord/test/cases/tasks/mysql_rake_test.rb
+++ b/activerecord/test/cases/tasks/mysql_rake_test.rb
@@ -59,7 +59,7 @@ if current_adapter?(:Mysql2Adapter)
       def test_when_database_created_successfully_outputs_info_to_stdout
         ActiveRecord::Tasks::DatabaseTasks.create @configuration
 
-        assert_equal $stdout.string, "Created database 'my-app-db'\n"
+        assert_equal "Created database 'my-app-db'\n", $stdout.string
       end
 
       def test_create_when_database_exists_outputs_info_to_stderr
@@ -69,7 +69,7 @@ if current_adapter?(:Mysql2Adapter)
 
         ActiveRecord::Tasks::DatabaseTasks.create @configuration
 
-        assert_equal $stderr.string, "Database 'my-app-db' already exists\n"
+        assert_equal "Database 'my-app-db' already exists\n", $stderr.string
       end
     end
 
@@ -205,7 +205,7 @@ if current_adapter?(:Mysql2Adapter)
       def test_when_database_dropped_successfully_outputs_info_to_stdout
         ActiveRecord::Tasks::DatabaseTasks.drop @configuration
 
-        assert_equal $stdout.string, "Dropped database 'my-app-db'\n"
+        assert_equal "Dropped database 'my-app-db'\n", $stdout.string
       end
     end
 
diff --git a/activerecord/test/cases/tasks/postgresql_rake_test.rb b/activerecord/test/cases/tasks/postgresql_rake_test.rb
index b8c8ec88f0..1a73d410d0 100644
--- a/activerecord/test/cases/tasks/postgresql_rake_test.rb
+++ b/activerecord/test/cases/tasks/postgresql_rake_test.rb
@@ -74,7 +74,7 @@ if current_adapter?(:PostgreSQLAdapter)
       def test_when_database_created_successfully_outputs_info_to_stdout
         ActiveRecord::Tasks::DatabaseTasks.create @configuration
 
-        assert_equal $stdout.string, "Created database 'my-app-db'\n"
+        assert_equal "Created database 'my-app-db'\n", $stdout.string
       end
 
       def test_create_when_database_exists_outputs_info_to_stderr
@@ -84,7 +84,7 @@ if current_adapter?(:PostgreSQLAdapter)
 
         ActiveRecord::Tasks::DatabaseTasks.create @configuration
 
-        assert_equal $stderr.string, "Database 'my-app-db' already exists\n"
+        assert_equal "Database 'my-app-db' already exists\n", $stderr.string
       end
     end
 
@@ -126,7 +126,7 @@ if current_adapter?(:PostgreSQLAdapter)
       def test_when_database_dropped_successfully_outputs_info_to_stdout
         ActiveRecord::Tasks::DatabaseTasks.drop @configuration
 
-        assert_equal $stdout.string, "Dropped database 'my-app-db'\n"
+        assert_equal "Dropped database 'my-app-db'\n", $stdout.string
       end
     end
 
diff --git a/activerecord/test/cases/tasks/sqlite_rake_test.rb b/activerecord/test/cases/tasks/sqlite_rake_test.rb
index 141048bfe7..0d917f3f6c 100644
--- a/activerecord/test/cases/tasks/sqlite_rake_test.rb
+++ b/activerecord/test/cases/tasks/sqlite_rake_test.rb
@@ -34,7 +34,7 @@ if current_adapter?(:SQLite3Adapter)
       def test_when_db_created_successfully_outputs_info_to_stdout
         ActiveRecord::Tasks::DatabaseTasks.create @configuration, "/rails/root"
 
-        assert_equal $stdout.string, "Created database '#{@database}'\n"
+        assert_equal "Created database '#{@database}'\n", $stdout.string
       end
 
       def test_db_create_when_file_exists
@@ -42,7 +42,7 @@ if current_adapter?(:SQLite3Adapter)
 
         ActiveRecord::Tasks::DatabaseTasks.create @configuration, "/rails/root"
 
-        assert_equal $stderr.string, "Database '#{@database}' already exists\n"
+        assert_equal "Database '#{@database}' already exists\n", $stderr.string
       end
 
       def test_db_create_with_file_does_nothing
@@ -128,7 +128,7 @@ if current_adapter?(:SQLite3Adapter)
       def test_when_db_dropped_successfully_outputs_info_to_stdout
         ActiveRecord::Tasks::DatabaseTasks.drop @configuration, "/rails/root"
 
-        assert_equal $stdout.string, "Dropped database '#{@database}'\n"
+        assert_equal "Dropped database '#{@database}'\n", $stdout.string
       end
     end
 
diff --git a/activerecord/test/cases/transaction_callbacks_test.rb b/activerecord/test/cases/transaction_callbacks_test.rb
index dba100f5c9..391bbe8877 100644
--- a/activerecord/test/cases/transaction_callbacks_test.rb
+++ b/activerecord/test/cases/transaction_callbacks_test.rb
@@ -449,6 +449,51 @@ class CallbacksOnMultipleActionsTest < ActiveRecord::TestCase
   end
 end
 
+class CallbacksOnDestroyUpdateActionRaceTest < ActiveRecord::TestCase
+  class TopicWithHistory < ActiveRecord::Base
+    self.table_name = :topics
+
+    def self.clear_history
+      @@history = []
+    end
+
+    def self.history
+      @@history ||= []
+    end
+  end
+
+  class TopicWithCallbacksOnDestroy < TopicWithHistory
+    after_commit(on: :destroy) { |record| record.class.history << :destroy }
+  end
+
+  class TopicWithCallbacksOnUpdate < TopicWithHistory
+    after_commit(on: :update) { |record| record.class.history << :update }
+  end
+
+  def test_trigger_once_on_multiple_deletions
+    TopicWithCallbacksOnDestroy.clear_history
+    topic = TopicWithCallbacksOnDestroy.new
+    topic.save
+    topic_clone = TopicWithCallbacksOnDestroy.find(topic.id)
+    topic.destroy
+    topic_clone.destroy
+
+    assert_equal [:destroy], TopicWithCallbacksOnDestroy.history
+  end
+
+  def test_trigger_on_update_where_row_was_deleted
+    TopicWithCallbacksOnUpdate.clear_history
+    topic = TopicWithCallbacksOnUpdate.new
+    topic.save
+    topic_clone = TopicWithCallbacksOnUpdate.find(topic.id)
+    topic.destroy
+    topic_clone.author_name = "Test Author"
+    topic_clone.save
+
+    assert_equal [], TopicWithCallbacksOnUpdate.history
+  end
+end
+
 class TransactionEnrollmentCallbacksTest < ActiveRecord::TestCase
   class TopicWithoutTransactionalEnrollmentCallbacks < ActiveRecord::Base
     self.table_name = :topics
diff --git a/activerecord/test/cases/type/unsigned_integer_test.rb b/activerecord/test/cases/type/unsigned_integer_test.rb
new file mode 100644
index 0000000000..1cd4dbc2c5
--- /dev/null
+++ b/activerecord/test/cases/type/unsigned_integer_test.rb
@@ -0,0 +1,17 @@
+require "cases/helper"
+
+module ActiveRecord
+  module Type
+    class UnsignedIntegerTest < ActiveRecord::TestCase
+      test "unsigned int max value is in range" do
+        assert_equal(4294967295, UnsignedInteger.new.serialize(4294967295))
+      end
+
+      test "minus value is out of range" do
+        assert_raises(ActiveModel::RangeError) do
+          UnsignedInteger.new.serialize(-1)
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/yaml_serialization_test.rb b/activerecord/test/cases/yaml_serialization_test.rb
index 5192e5050a..1571b31329 100644
--- a/activerecord/test/cases/yaml_serialization_test.rb
+++ b/activerecord/test/cases/yaml_serialization_test.rb
@@ -95,7 +95,7 @@ class YamlSerializationTest < ActiveRecord::TestCase
     topic = YAML.load(yaml_fixture("rails_4_1"))
 
     assert topic.new_record?
-    assert_equal nil, topic.id
+    assert_nil topic.id
     assert_equal "The First Topic", topic.title
     assert_equal({ omg: :lol }, topic.content)
   end
diff --git a/activerecord/test/fixtures/naked/yml/courses_with_invalid_key.yml b/activerecord/test/fixtures/naked/yml/courses_with_invalid_key.yml
new file mode 100644
index 0000000000..6f9da79b45
--- /dev/null
+++ b/activerecord/test/fixtures/naked/yml/courses_with_invalid_key.yml
@@ -0,0 +1,3 @@
+one:
+  id: 1
+two: ['not a hash']
diff --git a/activerecord/test/fixtures/other_dogs.yml b/activerecord/test/fixtures/other_dogs.yml
new file mode 100644
index 0000000000..b576861929
--- /dev/null
+++ b/activerecord/test/fixtures/other_dogs.yml
@@ -0,0 +1,2 @@
+lassie:
+  id: 1
diff --git a/activerecord/test/models/company_in_module.rb b/activerecord/test/models/company_in_module.rb
index 682f99e365..0782c1eff4 100644
--- a/activerecord/test/models/company_in_module.rb
+++ b/activerecord/test/models/company_in_module.rb
@@ -88,7 +88,7 @@ module MyApplication
 
       validate :check_empty_credit_limit
 
-      protected
+      private
 
         def check_empty_credit_limit
           errors.add("credit_card", :blank) if credit_card.blank?
diff --git a/activerecord/test/models/other_dog.rb b/activerecord/test/models/other_dog.rb
new file mode 100644
index 0000000000..418caf34be
--- /dev/null
+++ b/activerecord/test/models/other_dog.rb
@@ -0,0 +1,5 @@
+require_dependency "models/arunit2_model"
+
+class OtherDog < ARUnit2Model
+  self.table_name = "dogs"
+end
diff --git a/activerecord/test/models/parrot.rb b/activerecord/test/models/parrot.rb
index 5b693664d4..1e5f9285a8 100644
--- a/activerecord/test/models/parrot.rb
+++ b/activerecord/test/models/parrot.rb
@@ -13,6 +13,11 @@ class Parrot < ActiveRecord::Base
   def cancel_save_callback_method
     throw(:abort)
   end
+
+  before_update :increment_updated_count
+  def increment_updated_count
+    self.updated_count += 1
+  end
 end
 
 class LiveParrot < Parrot
diff --git a/activerecord/test/models/subject.rb b/activerecord/test/models/subject.rb
index 29e290825e..504f68a296 100644
--- a/activerecord/test/models/subject.rb
+++ b/activerecord/test/models/subject.rb
@@ -5,7 +5,7 @@ class Subject < ActiveRecord::Base
   # as otherwise synonym test was failing
   after_initialize :set_email_address
 
-  protected
+  private
     def set_email_address
       unless persisted?
         self.author_email_address = "test@test.com"
diff --git a/activerecord/test/models/topic.rb b/activerecord/test/models/topic.rb
index db04735d01..0420e2d15c 100644
--- a/activerecord/test/models/topic.rb
+++ b/activerecord/test/models/topic.rb
@@ -73,7 +73,7 @@ class Topic < ActiveRecord::Base
     write_attribute(:approved, val)
   end
 
-  protected
+  private
 
     def default_written_on
       self.written_on = Time.now unless attribute_present?("written_on")
diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index d889f46031..ba6f5de894 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -54,7 +54,7 @@ ActiveRecord::Schema.define do
 
   create_table :authors, force: true do |t|
     t.string :name, null: false
-    t.integer :author_address_id
+    t.bigint :author_address_id
     t.integer :author_address_extra_id
     t.string :organization_id
     t.string :owned_essay_id
@@ -126,6 +126,9 @@ ActiveRecord::Schema.define do
     t.timestamps null: false
   end
 
+  create_table :old_cars, id: :integer, force: true do |t|
+  end
+
   create_table :carriers, force: true
 
   create_table :categories, force: true do |t|
@@ -303,7 +306,7 @@ ActiveRecord::Schema.define do
   end
 
   create_table :engines, force: true do |t|
-    t.integer :car_id
+    t.bigint :car_id
   end
 
   create_table :entrants, force: true do |t|
@@ -571,6 +574,7 @@ ActiveRecord::Schema.define do
     t.column :color, :string
     t.column :parrot_sti_class, :string
     t.column :killer_id, :integer
+    t.column :updated_count, :integer, default: 0
     if subsecond_precision_supported?
       t.column :created_at, :datetime, precision: 0
       t.column :created_on, :datetime, precision: 0
@@ -1004,7 +1008,7 @@ ActiveRecord::Schema.define do
   if supports_foreign_keys?
     # fk_test_has_fk should be before fk_test_has_pk
     create_table :fk_test_has_fk, force: true do |t|
-      t.integer :fk_id, null: false
+      t.bigint :fk_id, null: false
     end
 
     create_table :fk_test_has_pk, force: true, primary_key: "pk_id" do |t|
@@ -1047,3 +1051,5 @@ Professor.connection.create_table :courses_professors, id: false, force: true do
   t.references :course
   t.references :professor
 end
+
+OtherDog.connection.create_table :dogs, force: true
diff --git a/activerecord/test/support/connection.rb b/activerecord/test/support/connection.rb
index c9260398e2..bc5af36a28 100644
--- a/activerecord/test/support/connection.rb
+++ b/activerecord/test/support/connection.rb
@@ -2,6 +2,7 @@ require "active_support/logger"
 require "models/college"
 require "models/course"
 require "models/professor"
+require "models/other_dog"
 
 module ARTest
   def self.connection_name