Merge branch 'master' into fix_26964

83 files changed, 629 insertions, 312 deletions

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? }