Merge branch 'master' into pr/18316

Conflicts:
	activerecord/CHANGELOG.md

90 files changed, 1160 insertions, 1032 deletions

diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 14af55f327..35bc09bb10 100644
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -1245,6 +1245,10 @@ module ActiveRecord
       #   that is the inverse of this <tt>has_many</tt> association. Does not work in combination
       #   with <tt>:through</tt> or <tt>:as</tt> options.
       #   See ActiveRecord::Associations::ClassMethods's overview on Bi-directional associations for more detail.
+      # [:extend]
+      #   Specifies a module or array of modules that will be extended into the association object returned.
+      #   Useful for defining methods on associations, especially when they should be shared between multiple
+      #   association objects.
       #
       # Option examples:
       #   has_many :comments, -> { order "posted_on" }
diff --git a/activerecord/lib/active_record/associations/association_scope.rb b/activerecord/lib/active_record/associations/association_scope.rb
index d06b7b3508..2416167834 100644
--- a/activerecord/lib/active_record/associations/association_scope.rb
+++ b/activerecord/lib/active_record/associations/association_scope.rb
@@ -2,42 +2,30 @@ module ActiveRecord
   module Associations
     class AssociationScope #:nodoc:
       def self.scope(association, connection)
-        INSTANCE.scope association, connection
-      end
-
-      class BindSubstitution
-        def initialize(block)
-          @block = block
-        end
-
-        def bind_value(scope, column, value, connection)
-          substitute = connection.substitute_at(column)
-          scope.bind_values += [[column, @block.call(value)]]
-          substitute
-        end
+        INSTANCE.scope(association, connection)
       end
 
       def self.create(&block)
-        block = block ? block : lambda { |val| val }
-        new BindSubstitution.new(block)
+        block ||= lambda { |val| val }
+        new(block)
       end
 
-      def initialize(bind_substitution)
-        @bind_substitution = bind_substitution
+      def initialize(value_transformation)
+        @value_transformation = value_transformation
       end
 
       INSTANCE = create
 
       def scope(association, connection)
-        klass         = association.klass
-        reflection    = association.reflection
-        scope         = klass.unscoped
-        owner         = association.owner
+        klass = association.klass
+        reflection = association.reflection
+        scope = klass.unscoped
+        owner = association.owner
         alias_tracker = AliasTracker.create connection, association.klass.table_name, klass.type_caster
         chain_head, chain_tail = get_chain(reflection, association, alias_tracker)
 
         scope.extending! Array(reflection.options[:extend])
-        add_constraints(scope, owner, klass, reflection, connection, chain_head, chain_tail)
+        add_constraints(scope, owner, klass, reflection, chain_head, chain_tail)
       end
 
       def join_type
@@ -61,43 +49,36 @@ module ActiveRecord
         binds
       end
 
+      protected
+
+      attr_reader :value_transformation
+
       private
       def join(table, constraint)
         table.create_join(table, table.create_on(constraint), join_type)
       end
 
-      def column_for(table_name, column_name, connection)
-        columns = connection.schema_cache.columns_hash(table_name)
-        columns[column_name]
-      end
-
-      def bind_value(scope, column, value, connection)
-        @bind_substitution.bind_value scope, column, value, connection
-      end
-
-      def bind(scope, table_name, column_name, value, connection)
-        column   = column_for table_name, column_name, connection
-        bind_value scope, column, value, connection
-      end
-
-      def last_chain_scope(scope, table, reflection, owner, connection, association_klass)
+      def last_chain_scope(scope, table, reflection, owner, association_klass)
         join_keys = reflection.join_keys(association_klass)
         key = join_keys.key
         foreign_key = join_keys.foreign_key
 
-        bind_val = bind scope, table.table_name, key.to_s, owner[foreign_key], connection
-        scope    = scope.where(table[key].eq(bind_val))
+        value = transform_value(owner[foreign_key])
+        scope = scope.where(table.name => { key => value })
 
         if reflection.type
-          value    = owner.class.base_class.name
-          bind_val = bind scope, table.table_name, reflection.type, value, connection
-          scope    = scope.where(table[reflection.type].eq(bind_val))
-        else
-          scope
+          polymorphic_type = transform_value(owner.class.base_class.name)
+          scope = scope.where(table.name => { reflection.type => polymorphic_type })
         end
+
+        scope
+      end
+
+      def transform_value(value)
+        value_transformation.call(value)
       end
 
-      def next_chain_scope(scope, table, reflection, connection, association_klass, foreign_table, next_reflection)
+      def next_chain_scope(scope, table, reflection, association_klass, foreign_table, next_reflection)
         join_keys = reflection.join_keys(association_klass)
         key = join_keys.key
         foreign_key = join_keys.foreign_key
@@ -105,9 +86,8 @@ module ActiveRecord
         constraint = table[key].eq(foreign_table[foreign_key])
 
         if reflection.type
-          value    = next_reflection.klass.base_class.name
-          bind_val = bind scope, table.table_name, reflection.type, value, connection
-          scope    = scope.where(table[reflection.type].eq(bind_val))
+          value = transform_value(next_reflection.klass.base_class.name)
+          scope = scope.where(table.name => { reflection.type => value })
         end
 
         scope = scope.joins(join(foreign_table, constraint))
@@ -138,10 +118,10 @@ module ActiveRecord
         [runtime_reflection, previous_reflection]
       end
 
-      def add_constraints(scope, owner, association_klass, refl, connection, chain_head, chain_tail)
+      def add_constraints(scope, owner, association_klass, refl, chain_head, chain_tail)
         owner_reflection = chain_tail
         table = owner_reflection.alias_name
-        scope = last_chain_scope(scope, table, owner_reflection, owner, connection, association_klass)
+        scope = last_chain_scope(scope, table, owner_reflection, owner, association_klass)
 
         reflection = chain_head
         loop do
@@ -151,7 +131,7 @@ module ActiveRecord
           unless reflection == chain_tail
             next_reflection = reflection.next
             foreign_table = next_reflection.alias_name
-            scope = next_chain_scope(scope, table, reflection, connection, association_klass, foreign_table, next_reflection)
+            scope = next_chain_scope(scope, table, reflection, association_klass, foreign_table, next_reflection)
           end
 
           # Exclude the scope of the association itself, because that
@@ -160,15 +140,14 @@ module ActiveRecord
             item  = eval_scope(reflection.klass, scope_chain_item, owner)
 
             if scope_chain_item == refl.scope
-              scope.merge! item.except(:where, :includes, :bind)
+              scope.merge! item.except(:where, :includes)
             end
 
             reflection.all_includes do
               scope.includes! item.includes_values
             end
 
-            scope.where_values += item.where_values
-            scope.bind_values  += item.bind_values
+            scope.where_clause += item.where_clause
             scope.order_values |= item.order_values
           end
 
diff --git a/activerecord/lib/active_record/associations/belongs_to_association.rb b/activerecord/lib/active_record/associations/belongs_to_association.rb
index c63b42e2a0..265a65c4c1 100644
--- a/activerecord/lib/active_record/associations/belongs_to_association.rb
+++ b/activerecord/lib/active_record/associations/belongs_to_association.rb
@@ -68,6 +68,9 @@ module ActiveRecord
         def increment_counter(counter_cache_name)
           if foreign_key_present?
             klass.increment_counter(counter_cache_name, target_id)
+            if target && !stale_target?
+              target.increment(counter_cache_name)
+            end
           end
         end
 
diff --git a/activerecord/lib/active_record/associations/builder/singular_association.rb b/activerecord/lib/active_record/associations/builder/singular_association.rb
index 1369212837..f6274c027e 100644
--- a/activerecord/lib/active_record/associations/builder/singular_association.rb
+++ b/activerecord/lib/active_record/associations/builder/singular_association.rb
@@ -31,7 +31,7 @@ module ActiveRecord::Associations::Builder
     def self.define_validations(model, reflection)
       super
       if reflection.options[:required]
-        model.validates_presence_of reflection.name
+        model.validates_presence_of reflection.name, message: :required
       end
     end
   end
diff --git a/activerecord/lib/active_record/associations/collection_association.rb b/activerecord/lib/active_record/associations/collection_association.rb
index f2c96e9a2a..4b7591e15c 100644
--- a/activerecord/lib/active_record/associations/collection_association.rb
+++ b/activerecord/lib/active_record/associations/collection_association.rb
@@ -151,6 +151,7 @@ module ActiveRecord
       # be chained. Since << flattens its argument list and inserts each record,
       # +push+ and +concat+ behave identically.
       def concat(*records)
+        records = records.flatten
         if owner.new_record?
           load_target
           concat_records(records)
@@ -549,7 +550,7 @@ module ActiveRecord
         def concat_records(records, should_raise = false)
           result = true
 
-          records.flatten.each do |record|
+          records.each do |record|
             raise_on_type_mismatch!(record)
             add_to_target(record) do |rec|
               result &&= insert_record(rec, true, should_raise) unless owner.new_record?
diff --git a/activerecord/lib/active_record/associations/has_many_association.rb b/activerecord/lib/active_record/associations/has_many_association.rb
index d7f655d00c..b574185561 100644
--- a/activerecord/lib/active_record/associations/has_many_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_association.rb
@@ -17,7 +17,7 @@ module ActiveRecord
           unless empty?
             record = klass.human_attribute_name(reflection.name).downcase
             owner.errors.add(:base, :"restrict_dependent_destroy.many", record: record)
-            false
+            throw(:abort)
           end
 
         else
@@ -101,7 +101,7 @@ module ActiveRecord
         end
 
         def update_counter_in_memory(difference, reflection = reflection())
-          if has_cached_counter?(reflection)
+          if counter_must_be_updated_by_has_many?(reflection)
             counter = cached_counter_attribute_name(reflection)
             owner[counter] += difference
             owner.send(:clear_attribute_changes, counter) # eww
@@ -118,18 +118,28 @@ module ActiveRecord
         #     it will be decremented twice.
         #
         # Hence this method.
-        def inverse_updates_counter_cache?(reflection = reflection())
+        def inverse_which_updates_counter_cache(reflection = reflection())
           counter_name = cached_counter_attribute_name(reflection)
-          inverse_updates_counter_named?(counter_name, reflection)
+          inverse_which_updates_counter_named(counter_name, reflection)
         end
+        alias inverse_updates_counter_cache? inverse_which_updates_counter_cache
 
-        def inverse_updates_counter_named?(counter_name, reflection = reflection())
-          reflection.klass._reflections.values.any? { |inverse_reflection|
+        def inverse_which_updates_counter_named(counter_name, reflection)
+          reflection.klass._reflections.values.find { |inverse_reflection|
             inverse_reflection.belongs_to? &&
             inverse_reflection.counter_cache_column == counter_name
           }
         end
 
+        def inverse_updates_counter_in_memory?(reflection)
+          inverse = inverse_which_updates_counter_cache(reflection)
+          inverse && inverse == reflection.inverse_of
+        end
+
+        def counter_must_be_updated_by_has_many?(reflection)
+          !inverse_updates_counter_in_memory?(reflection) && has_cached_counter?(reflection)
+        end
+
         def delete_count(method, scope)
           if method == :delete_all
             scope.delete_all
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 7a050ca224..4fcbc98c62 100644
--- a/activerecord/lib/active_record/associations/has_many_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -1,5 +1,3 @@
-require 'active_support/core_ext/string/filters'
-
 module ActiveRecord
   # = Active Record Has Many Through Association
   module Associations
@@ -49,16 +47,7 @@ module ActiveRecord
         end
 
         save_through_record(record)
-        if has_cached_counter? && !through_reflection_updates_counter_cache?
-          ActiveSupport::Deprecation.warn(<<-MSG.squish)
-            Automatic updating of counter caches on through associations has been
-            deprecated, and will be removed in Rails 5. Instead, please set the
-            appropriate `counter_cache` options on the `has_many` and `belongs_to`
-            for your associations to #{through_reflection.name}.
-          MSG
 
-          update_counter_in_database(1)
-        end
         record
       end
 
@@ -154,7 +143,7 @@ module ActiveRecord
               stmt.from scope.klass.arel_table
               stmt.wheres = arel.constraints
 
-              count = scope.klass.connection.delete(stmt, 'SQL', scope.bind_values)
+              count = scope.klass.connection.delete(stmt, 'SQL', scope.bound_attributes)
             end
           when :nullify
             count = scope.update_all(source_reflection.foreign_key => nil)
@@ -211,11 +200,6 @@ module ActiveRecord
         def invertible_for?(record)
           false
         end
-
-        def through_reflection_updates_counter_cache?
-          counter_name = cached_counter_attribute_name
-          inverse_updates_counter_named?(counter_name, through_reflection)
-        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/associations/has_one_association.rb b/activerecord/lib/active_record/associations/has_one_association.rb
index 74b8c53758..41a75b820e 100644
--- a/activerecord/lib/active_record/associations/has_one_association.rb
+++ b/activerecord/lib/active_record/associations/has_one_association.rb
@@ -13,7 +13,7 @@ module ActiveRecord
           if load_target
             record = klass.human_attribute_name(reflection.name).downcase
             owner.errors.add(:base, :"restrict_dependent_destroy.one", record: record)
-            false
+            throw(:abort)
           end
 
         else
diff --git a/activerecord/lib/active_record/associations/join_dependency/join_association.rb b/activerecord/lib/active_record/associations/join_dependency/join_association.rb
index c1ef86a95b..a6ad09a38a 100644
--- a/activerecord/lib/active_record/associations/join_dependency/join_association.rb
+++ b/activerecord/lib/active_record/associations/join_dependency/join_association.rb
@@ -25,7 +25,7 @@ module ActiveRecord
 
         def join_constraints(foreign_table, foreign_klass, node, join_type, tables, scope_chain, chain)
           joins         = []
-          bind_values   = []
+          binds         = []
           tables        = tables.reverse
 
           scope_chain_index = 0
@@ -66,7 +66,7 @@ module ActiveRecord
             end
 
             if rel && !rel.arel.constraints.empty?
-              bind_values.concat rel.bind_values
+              binds += rel.bound_attributes
               constraint = constraint.and rel.arel.constraints
             end
 
@@ -75,7 +75,7 @@ module ActiveRecord
               column = klass.columns_hash[reflection.type.to_s]
 
               substitute = klass.connection.substitute_at(column)
-              bind_values.push [column, value]
+              binds << Relation::QueryAttribute.new(column.name, value, klass.type_for_attribute(column.name))
               constraint = constraint.and table[reflection.type].eq substitute
             end
 
@@ -85,7 +85,7 @@ module ActiveRecord
             foreign_table, foreign_klass = table, klass
           end
 
-          JoinInformation.new joins, bind_values
+          JoinInformation.new joins, binds
         end
 
         #  Builds equality condition.
diff --git a/activerecord/lib/active_record/associations/preloader.rb b/activerecord/lib/active_record/associations/preloader.rb
index 4358f3b581..97f4bd3811 100644
--- a/activerecord/lib/active_record/associations/preloader.rb
+++ b/activerecord/lib/active_record/associations/preloader.rb
@@ -89,7 +89,7 @@ module ActiveRecord
       #   { author: :avatar }
       #   [ :books, { author: :avatar } ]
 
-      NULL_RELATION = Struct.new(:values, :bind_values).new({}, [])
+      NULL_RELATION = Struct.new(:values, :where_clause, :joins_values).new({}, Relation::WhereClause.empty, [])
 
       def preload(records, associations, preload_scope = nil)
         records       = Array.wrap(records).compact.uniq
diff --git a/activerecord/lib/active_record/associations/preloader/association.rb b/activerecord/lib/active_record/associations/preloader/association.rb
index a6e1a24360..1dc8bff193 100644
--- a/activerecord/lib/active_record/associations/preloader/association.rb
+++ b/activerecord/lib/active_record/associations/preloader/association.rb
@@ -131,18 +131,19 @@ module ActiveRecord
         def build_scope
           scope = klass.unscoped
 
-          values         = reflection_scope.values
-          reflection_binds = reflection_scope.bind_values
+          values = reflection_scope.values
           preload_values = preload_scope.values
-          preload_binds  = preload_scope.bind_values
 
-          scope.where_values      = Array(values[:where])      + Array(preload_values[:where])
+          scope.where_clause = reflection_scope.where_clause + preload_scope.where_clause
           scope.references_values = Array(values[:references]) + Array(preload_values[:references])
-          scope.bind_values       = (reflection_binds + preload_binds)
 
-          scope._select!   preload_values[:select] || values[:select] || table[Arel.star]
+          scope._select! preload_values[:select] || values[:select] || table[Arel.star]
           scope.includes! preload_values[:includes] || values[:includes]
-          scope.joins! preload_values[:joins] || values[:joins]
+          if preload_scope.joins_values.any?
+            scope.joins!(preload_scope.joins_values)
+          else
+            scope.joins!(reflection_scope.joins_values)
+          end
           scope.order! preload_values[:order] || values[:order]
 
           if preload_values[:readonly] || values[:readonly]
diff --git a/activerecord/lib/active_record/associations/preloader/through_association.rb b/activerecord/lib/active_record/associations/preloader/through_association.rb
index 12bf3ef138..56aa23b173 100644
--- a/activerecord/lib/active_record/associations/preloader/through_association.rb
+++ b/activerecord/lib/active_record/associations/preloader/through_association.rb
@@ -78,10 +78,9 @@ module ActiveRecord
           if options[:source_type]
             scope.where! reflection.foreign_type => options[:source_type]
           else
-            unless reflection_scope.where_values.empty?
+            unless reflection_scope.where_clause.empty?
               scope.includes_values = Array(reflection_scope.values[:includes] || options[:source])
-              scope.where_values    = reflection_scope.values[:where]
-              scope.bind_values     = reflection_scope.bind_values
+              scope.where_clause = reflection_scope.where_clause
             end
 
             scope.references! reflection_scope.values[:references]
diff --git a/activerecord/lib/active_record/associations/through_association.rb b/activerecord/lib/active_record/associations/through_association.rb
index 09828dbd9b..3ce9cffdbc 100644
--- a/activerecord/lib/active_record/associations/through_association.rb
+++ b/activerecord/lib/active_record/associations/through_association.rb
@@ -18,7 +18,7 @@ module ActiveRecord
 
             reflection_scope = reflection.scope
             if reflection_scope && reflection_scope.arity.zero?
-              relation.merge!(reflection_scope)
+              relation = relation.merge(reflection_scope)
             end
 
             scope.merge!(
diff --git a/activerecord/lib/active_record/attribute.rb b/activerecord/lib/active_record/attribute.rb
index 88536eaac0..91886f1324 100644
--- a/activerecord/lib/active_record/attribute.rb
+++ b/activerecord/lib/active_record/attribute.rb
@@ -51,7 +51,7 @@ module ActiveRecord
     end
 
     def changed_in_place_from?(old_value)
-      type.changed_in_place?(old_value, value)
+      has_been_read? && type.changed_in_place?(old_value, value)
     end
 
     def with_value_from_user(value)
@@ -66,6 +66,10 @@ module ActiveRecord
       self.class.with_cast_value(name, value, type)
     end
 
+    def with_type(type)
+      self.class.new(name, value_before_type_cast, type)
+    end
+
     def type_cast(*)
       raise NotImplementedError
     end
@@ -74,12 +78,25 @@ module ActiveRecord
       true
     end
 
+    def came_from_user?
+      false
+    end
+
+    def has_been_read?
+      defined?(@value)
+    end
+
     def ==(other)
       self.class == other.class &&
         name == other.name &&
         value_before_type_cast == other.value_before_type_cast &&
         type == other.type
     end
+    alias eql? ==
+
+    def hash
+      [self.class, name, value_before_type_cast, type].hash
+    end
 
     protected
 
@@ -99,6 +116,10 @@ module ActiveRecord
       def type_cast(value)
         type.type_cast_from_user(value)
       end
+
+      def came_from_user?
+        true
+      end
     end
 
     class WithCastValue < Attribute # :nodoc:
@@ -120,6 +141,10 @@ module ActiveRecord
         nil
       end
 
+      def with_type(type)
+        self.class.with_cast_value(name, nil, type)
+      end
+
       def with_value_from_database(value)
         raise ActiveModel::MissingAttributeError, "can't write unknown attribute `#{name}`"
       end
@@ -144,6 +169,6 @@ module ActiveRecord
         false
       end
     end
-    private_constant :FromDatabase, :FromUser, :Null, :Uninitialized
+    private_constant :FromDatabase, :FromUser, :Null, :Uninitialized, :WithCastValue
   end
 end
diff --git a/activerecord/lib/active_record/attribute_assignment.rb b/activerecord/lib/active_record/attribute_assignment.rb
index bf64830417..fdc90df5b6 100644
--- a/activerecord/lib/active_record/attribute_assignment.rb
+++ b/activerecord/lib/active_record/attribute_assignment.rb
@@ -3,63 +3,32 @@ require 'active_model/forbidden_attributes_protection'
 module ActiveRecord
   module AttributeAssignment
     extend ActiveSupport::Concern
-    include ActiveModel::ForbiddenAttributesProtection
-
-    # Allows you to set all the attributes by passing in a hash of attributes with
-    # keys matching the attribute names (which again matches the column names).
-    #
-    # If the passed hash responds to <tt>permitted?</tt> method and the return value
-    # of this method is +false+ an <tt>ActiveModel::ForbiddenAttributesError</tt>
-    # exception is raised.
-    #
-    #   cat = Cat.new(name: "Gorby", status: "yawning")
-    #   cat.attributes # =>  { "name" => "Gorby", "status" => "yawning", "created_at" => nil, "updated_at" => nil}
-    #   cat.assign_attributes(status: "sleeping")
-    #   cat.attributes # =>  { "name" => "Gorby", "status" => "sleeping", "created_at" => nil, "updated_at" => nil }
-    #
-    # New attributes will be persisted in the database when the object is saved.
-    #
-    # Aliased to <tt>attributes=</tt>.
-    def assign_attributes(new_attributes)
-      if !new_attributes.respond_to?(:stringify_keys)
-        raise ArgumentError, "When assigning attributes, you must pass a hash as an argument."
-      end
-      return if new_attributes.blank?
+    include ActiveModel::AttributeAssignment
+
+    # Alias for `assign_attributes`. See +ActiveModel::AttributeAssignment+.
+    def attributes=(attributes)
+      assign_attributes(attributes)
+    end
 
-      attributes                  = new_attributes.stringify_keys
-      multi_parameter_attributes  = []
-      nested_parameter_attributes = []
+    private
 
-      attributes = sanitize_for_mass_assignment(attributes)
+    def _assign_attributes(attributes) # :nodoc:
+      multi_parameter_attributes  = {}
+      nested_parameter_attributes = {}
 
       attributes.each do |k, v|
         if k.include?("(")
-          multi_parameter_attributes << [ k, v ]
+          multi_parameter_attributes[k] = attributes.delete(k)
         elsif v.is_a?(Hash)
-          nested_parameter_attributes << [ k, v ]
-        else
-          _assign_attribute(k, v)
+          nested_parameter_attributes[k] = attributes.delete(k)
         end
       end
+      super(attributes)
 
       assign_nested_parameter_attributes(nested_parameter_attributes) unless nested_parameter_attributes.empty?
       assign_multiparameter_attributes(multi_parameter_attributes) unless multi_parameter_attributes.empty?
     end
 
-    alias attributes= assign_attributes
-
-    private
-
-    def _assign_attribute(k, v)
-      public_send("#{k}=", v)
-    rescue NoMethodError
-      if respond_to?("#{k}=")
-        raise
-      else
-        raise UnknownAttributeError.new(self, k)
-      end
-    end
-
     # Assign any deferred nested attributes after the base attributes have been set.
     def assign_nested_parameter_attributes(pairs)
       pairs.each { |k, v| _assign_attribute(k, v) }
diff --git a/activerecord/lib/active_record/attribute_decorators.rb b/activerecord/lib/active_record/attribute_decorators.rb
index 5b96623b6e..7d0ae32411 100644
--- a/activerecord/lib/active_record/attribute_decorators.rb
+++ b/activerecord/lib/active_record/attribute_decorators.rb
@@ -15,7 +15,7 @@ module ActiveRecord
       end
 
       def decorate_matching_attribute_types(matcher, decorator_name, &block)
-        clear_caches_calculated_from_columns
+        reload_schema_from_cache
         decorator_name = decorator_name.to_s
 
         # Create new hashes so we don't modify parent classes
@@ -24,10 +24,11 @@ module ActiveRecord
 
       private
 
-      def add_user_provided_columns(*)
-        super.map do |column|
-          decorated_type = attribute_type_decorations.apply(column.name, column.cast_type)
-          column.with_type(decorated_type)
+      def load_schema!
+        super
+        attribute_types.each do |name, type|
+          decorated_type = attribute_type_decorations.apply(name, type)
+          define_attribute(name, decorated_type)
         end
       end
     end
diff --git a/activerecord/lib/active_record/attribute_methods.rb b/activerecord/lib/active_record/attribute_methods.rb
index b7edac791e..9d58a19304 100644
--- a/activerecord/lib/active_record/attribute_methods.rb
+++ b/activerecord/lib/active_record/attribute_methods.rb
@@ -83,7 +83,7 @@ module ActiveRecord
         generated_attribute_methods.synchronize do
           return false if @attribute_methods_generated
           superclass.define_attribute_methods unless self == base_class
-          super(column_names)
+          super(attribute_names)
           @attribute_methods_generated = true
         end
         true
@@ -185,14 +185,15 @@ module ActiveRecord
       #   # => ["id", "created_at", "updated_at", "name", "age"]
       def attribute_names
         @attribute_names ||= if !abstract_class? && table_exists?
-            column_names
+            attribute_types.keys
           else
             []
           end
       end
 
       # Returns the column object for the named attribute.
-      # Returns nil if the named attribute does not exist.
+      # Returns a +ActiveRecord::ConnectionAdapters::NullColumn+ if the
+      # named attribute does not exist.
       #
       #   class Person < ActiveRecord::Base
       #   end
@@ -202,17 +203,12 @@ module ActiveRecord
       #   # => #<ActiveRecord::ConnectionAdapters::Column:0x007ff4ab083980 @name="name", @sql_type="varchar(255)", @null=true, ...>
       #
       #   person.column_for_attribute(:nothing)
-      #   # => nil
+      #   # => #<ActiveRecord::ConnectionAdapters::NullColumn:0xXXX @name=nil, @sql_type=nil, @cast_type=#<Type::Value>, ...>
       def column_for_attribute(name)
-        column = columns_hash[name.to_s]
-        if column.nil?
-          ActiveSupport::Deprecation.warn(<<-MSG.squish)
-            `#column_for_attribute` will return a null object for non-existent
-            columns in Rails 5. Use `#has_attribute?` if you need to check for
-            an attribute's existence.
-          MSG
+        name = name.to_s
+        columns_hash.fetch(name) do
+          ConnectionAdapters::NullColumn.new(name)
         end
-        column
       end
     end
 
@@ -373,6 +369,39 @@ module ActiveRecord
       write_attribute(attr_name, value)
     end
 
+    # Returns the name of all database fields which have been read from this
+    # model. This can be useful in development mode to determine which fields
+    # need to be selected. For performance critical pages, selecting only the
+    # required fields can be an easy performance win (assuming you aren't using
+    # all of the fields on the model).
+    #
+    # For example:
+    #
+    # class PostsController < ActionController::Base
+    #   after_action :print_accessed_fields, only: :index
+    #
+    #   def index
+    #     @posts = Post.all
+    #   end
+    #
+    #   private
+    #
+    #   def print_accessed_fields
+    #     p @posts.first.accessed_fields
+    #   end
+    # end
+    #
+    # Which allows you to quickly change your code to:
+    #
+    # class PostsController < ActionController::Base
+    #   def index
+    #     @posts = Post.select(:id, :title, :author_id, :updated_at)
+    #   end
+    # end
+    def accessed_fields
+      @attributes.accessed
+    end
+
     protected
 
     def clone_attribute_value(reader_method, attribute_name) # :nodoc:
diff --git a/activerecord/lib/active_record/attribute_methods/before_type_cast.rb b/activerecord/lib/active_record/attribute_methods/before_type_cast.rb
index fd61febd57..56c1898551 100644
--- a/activerecord/lib/active_record/attribute_methods/before_type_cast.rb
+++ b/activerecord/lib/active_record/attribute_methods/before_type_cast.rb
@@ -28,6 +28,7 @@ module ActiveRecord
 
       included do
         attribute_method_suffix "_before_type_cast"
+        attribute_method_suffix "_came_from_user?"
       end
 
       # Returns the value of the attribute identified by +attr_name+ before
@@ -66,6 +67,10 @@ module ActiveRecord
       def attribute_before_type_cast(attribute_name)
         read_attribute_before_type_cast(attribute_name)
       end
+
+      def attribute_came_from_user?(attribute_name)
+        @attributes[attribute_name].came_from_user?
+      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/attribute_methods/dirty.rb b/activerecord/lib/active_record/attribute_methods/dirty.rb
index d5702accaf..7ba907f786 100644
--- a/activerecord/lib/active_record/attribute_methods/dirty.rb
+++ b/activerecord/lib/active_record/attribute_methods/dirty.rb
@@ -108,7 +108,7 @@ module ActiveRecord
       end
 
       def save_changed_attribute(attr, old_value)
-        if attribute_changed?(attr)
+        if attribute_changed_by_setter?(attr)
           clear_attribute_changes(attr) unless _field_changed?(attr, old_value)
         else
           set_attribute_was(attr, old_value) if _field_changed?(attr, old_value)
@@ -131,10 +131,8 @@ module ActiveRecord
         partial_writes? ? super(keys_for_partial_write) : super
       end
 
-      # Serialized attributes should always be written in case they've been
-      # changed in place.
       def keys_for_partial_write
-        changed
+        changed & self.class.column_names
       end
 
       def _field_changed?(attr, old_value)
@@ -165,7 +163,7 @@ module ActiveRecord
       end
 
       def store_original_raw_attribute(attr_name)
-        original_raw_attributes[attr_name] = @attributes[attr_name].value_for_database
+        original_raw_attributes[attr_name] = @attributes[attr_name].value_for_database rescue nil
       end
 
       def store_original_raw_attributes
diff --git a/activerecord/lib/active_record/attribute_methods/query.rb b/activerecord/lib/active_record/attribute_methods/query.rb
index dc689f399a..83b858aae7 100644
--- a/activerecord/lib/active_record/attribute_methods/query.rb
+++ b/activerecord/lib/active_record/attribute_methods/query.rb
@@ -15,6 +15,7 @@ module ActiveRecord
         when false, nil  then false
         else
           column = self.class.columns_hash[attr_name]
+          type = self.class.type_for_attribute(attr_name)
           if column.nil?
             if Numeric === value || value !~ /[^0-9]/
               !value.to_i.zero?
@@ -22,7 +23,7 @@ module ActiveRecord
               return false if ActiveRecord::ConnectionAdapters::Column::FALSE_VALUES.include?(value)
               !value.blank?
             end
-          elsif column.number?
+          elsif type.number?
             !value.zero?
           else
             !value.blank?
diff --git a/activerecord/lib/active_record/attribute_methods/read.rb b/activerecord/lib/active_record/attribute_methods/read.rb
index 20f0936e52..24e30b6608 100644
--- a/activerecord/lib/active_record/attribute_methods/read.rb
+++ b/activerecord/lib/active_record/attribute_methods/read.rb
@@ -1,5 +1,3 @@
-require 'active_support/core_ext/module/method_transplanting'
-
 module ActiveRecord
   module AttributeMethods
     module Read
@@ -36,42 +34,24 @@ module ActiveRecord
       extend ActiveSupport::Concern
 
       module ClassMethods
-        [:cache_attributes, :cached_attributes, :cache_attribute?].each do |method_name|
-          define_method method_name do |*|
-            cached_attributes_deprecation_warning(method_name)
-            true
-          end
-        end
-
         protected
 
-        def cached_attributes_deprecation_warning(method_name)
-          ActiveSupport::Deprecation.warn "Calling `#{method_name}` is no longer necessary. All attributes are cached."
-        end
+        def define_method_attribute(name)
+          safe_name = name.unpack('h*').first
+          temp_method = "__temp__#{safe_name}"
 
-        if Module.methods_transplantable?
-          def define_method_attribute(name)
-            method = ReaderMethodCache[name]
-            generated_attribute_methods.module_eval { define_method name, method }
-          end
-        else
-          def define_method_attribute(name)
-            safe_name = name.unpack('h*').first
-            temp_method = "__temp__#{safe_name}"
+          ActiveRecord::AttributeMethods::AttrNames.set_name_cache safe_name, name
 
-            ActiveRecord::AttributeMethods::AttrNames.set_name_cache safe_name, name
-
-            generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
-              def #{temp_method}
-                name = ::ActiveRecord::AttributeMethods::AttrNames::ATTR_#{safe_name}
-                _read_attribute(name) { |n| missing_attribute(n, caller) }
-              end
-            STR
-
-            generated_attribute_methods.module_eval do
-              alias_method name, temp_method
-              undef_method temp_method
+          generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
+            def #{temp_method}
+              name = ::ActiveRecord::AttributeMethods::AttrNames::ATTR_#{safe_name}
+              _read_attribute(name) { |n| missing_attribute(n, caller) }
             end
+          STR
+
+          generated_attribute_methods.module_eval do
+            alias_method name, temp_method
+            undef_method temp_method
           end
         end
       end
@@ -92,12 +72,9 @@ module ActiveRecord
       def _read_attribute(attr_name) # :nodoc:
         @attributes.fetch_value(attr_name.to_s) { |n| yield n if block_given? }
       end
+      alias :attribute :_read_attribute
+      private :attribute
 
-      private
-
-      def attribute(attribute_name)
-        _read_attribute(attribute_name)
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/attribute_methods/serialization.rb b/activerecord/lib/active_record/attribute_methods/serialization.rb
index e5ec5ddca5..d0d8a968c5 100644
--- a/activerecord/lib/active_record/attribute_methods/serialization.rb
+++ b/activerecord/lib/active_record/attribute_methods/serialization.rb
@@ -1,5 +1,3 @@
-require 'active_support/core_ext/string/filters'
-
 module ActiveRecord
   module AttributeMethods
     module Serialization
@@ -51,19 +49,6 @@ module ActiveRecord
             Type::Serialized.new(type, coder)
           end
         end
-
-        def serialized_attributes
-          ActiveSupport::Deprecation.warn(<<-MSG.squish)
-            `serialized_attributes` is deprecated without replacement, and will
-            be removed in Rails 5.0.
-          MSG
-
-          @serialized_attributes ||= Hash[
-            columns.select { |t| t.cast_type.is_a?(Type::Serialized) }.map { |c|
-              [c.name, c.cast_type.coder]
-            }
-          ]
-        end
       end
     end
   end
diff --git a/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb b/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
index 777f7ab4d7..75cc88d4ee 100644
--- a/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
+++ b/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
@@ -13,7 +13,7 @@ module ActiveRecord
             value.map { |v| type_cast_from_user(v) }
           elsif value.respond_to?(:in_time_zone)
             begin
-              value.in_time_zone || super
+              user_input_in_time_zone(value) || super
             rescue ArgumentError
               nil
             end
@@ -39,6 +39,9 @@ module ActiveRecord
 
         class_attribute :skip_time_zone_conversion_for_attributes, instance_writer: false
         self.skip_time_zone_conversion_for_attributes = []
+
+        class_attribute :time_zone_aware_types, instance_writer: false
+        self.time_zone_aware_types = [:datetime, :not_explicitly_configured]
       end
 
       module ClassMethods
@@ -59,9 +62,31 @@ module ActiveRecord
         end
 
         def create_time_zone_conversion_attribute?(name, cast_type)
-          time_zone_aware_attributes &&
-            !self.skip_time_zone_conversion_for_attributes.include?(name.to_sym) &&
-            (:datetime == cast_type.type)
+          enabled_for_column = time_zone_aware_attributes &&
+            !self.skip_time_zone_conversion_for_attributes.include?(name.to_sym)
+          result = enabled_for_column &&
+            time_zone_aware_types.include?(cast_type.type)
+
+          if enabled_for_column &&
+            !result &&
+            cast_type.type == :time &&
+            time_zone_aware_types.include?(:not_explicitly_configured)
+            ActiveSupport::Deprecation.warn(<<-MESSAGE)
+              Time columns will become time zone aware in Rails 5.1. This
+              still causes `String`s to be parsed as if they were in `Time.zone`,
+              and `Time`s to be converted to `Time.zone`.
+
+              To keep the old behavior, you must add the following to your initializer:
+
+                  config.active_record.time_zone_aware_types = [:datetime]
+
+              To silence this deprecation warning, add the following:
+
+                  config.active_record.time_zone_aware_types << :time
+            MESSAGE
+          end
+
+          result
         end
       end
     end
diff --git a/activerecord/lib/active_record/attribute_methods/write.rb b/activerecord/lib/active_record/attribute_methods/write.rb
index 16804f86bf..ab017c7b54 100644
--- a/activerecord/lib/active_record/attribute_methods/write.rb
+++ b/activerecord/lib/active_record/attribute_methods/write.rb
@@ -1,5 +1,3 @@
-require 'active_support/core_ext/module/method_transplanting'
-
 module ActiveRecord
   module AttributeMethods
     module Write
@@ -25,27 +23,18 @@ module ActiveRecord
       module ClassMethods
         protected
 
-        if Module.methods_transplantable?
-          def define_method_attribute=(name)
-            method = WriterMethodCache[name]
-            generated_attribute_methods.module_eval {
-              define_method "#{name}=", method
-            }
-          end
-        else
-          def define_method_attribute=(name)
-            safe_name = name.unpack('h*').first
-            ActiveRecord::AttributeMethods::AttrNames.set_name_cache safe_name, name
+        def define_method_attribute=(name)
+          safe_name = name.unpack('h*').first
+          ActiveRecord::AttributeMethods::AttrNames.set_name_cache safe_name, name
 
-            generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
-              def __temp__#{safe_name}=(value)
-                name = ::ActiveRecord::AttributeMethods::AttrNames::ATTR_#{safe_name}
-                write_attribute(name, value)
-              end
-              alias_method #{(name + '=').inspect}, :__temp__#{safe_name}=
-              undef_method :__temp__#{safe_name}=
-            STR
-          end
+          generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
+            def __temp__#{safe_name}=(value)
+              name = ::ActiveRecord::AttributeMethods::AttrNames::ATTR_#{safe_name}
+              write_attribute(name, value)
+            end
+            alias_method #{(name + '=').inspect}, :__temp__#{safe_name}=
+            undef_method :__temp__#{safe_name}=
+          STR
         end
       end
 
diff --git a/activerecord/lib/active_record/attribute_set.rb b/activerecord/lib/active_record/attribute_set.rb
index 66fcaf6945..9142317646 100644
--- a/activerecord/lib/active_record/attribute_set.rb
+++ b/activerecord/lib/active_record/attribute_set.rb
@@ -10,6 +10,10 @@ module ActiveRecord
       attributes[name] || Attribute.null(name)
     end
 
+    def []=(name, value)
+      attributes[name] = value
+    end
+
     def values_before_type_cast
       attributes.transform_values(&:value_before_type_cast)
     end
@@ -24,7 +28,7 @@ module ActiveRecord
     end
 
     def keys
-      attributes.initialized_keys
+      attributes.each_key.select { |name| self[name].initialized? }
     end
 
     def fetch_value(name)
@@ -49,7 +53,7 @@ module ActiveRecord
     end
 
     def initialize_dup(_)
-      @attributes = attributes.dup
+      @attributes = attributes.deep_dup
       super
     end
 
@@ -64,6 +68,10 @@ module ActiveRecord
       end
     end
 
+    def accessed
+      attributes.select { |_, attr| attr.has_been_read? }.keys
+    end
+
     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 3a76f5262d..0f3c285a80 100644
--- a/activerecord/lib/active_record/attribute_set/builder.rb
+++ b/activerecord/lib/active_record/attribute_set/builder.rb
@@ -20,7 +20,7 @@ module ActiveRecord
   end
 
   class LazyAttributeHash # :nodoc:
-    delegate :select, :transform_values, to: :materialize
+    delegate :select, :transform_values, :each_key, to: :materialize
 
     def initialize(types, values, additional_types)
       @types = types
@@ -45,10 +45,6 @@ module ActiveRecord
       delegate_hash[key] = value
     end
 
-    def initialized_keys
-      delegate_hash.keys | values.keys
-    end
-
     def initialize_dup(_)
       @delegate_hash = delegate_hash.transform_values(&:dup)
       super
diff --git a/activerecord/lib/active_record/attributes.rb b/activerecord/lib/active_record/attributes.rb
index aafb990bc1..c1b69092bb 100644
--- a/activerecord/lib/active_record/attributes.rb
+++ b/activerecord/lib/active_record/attributes.rb
@@ -5,14 +5,12 @@ module ActiveRecord
     Type = ActiveRecord::Type
 
     included do
-      class_attribute :user_provided_columns, instance_accessor: false # :internal:
-      class_attribute :user_provided_defaults, instance_accessor: false # :internal:
-      self.user_provided_columns = {}
-      self.user_provided_defaults = {}
+      class_attribute :user_provided_types, instance_accessor: false # :internal:
+      self.user_provided_types = {}
     end
 
     module ClassMethods # :nodoc:
-      # Defines or overrides a attribute on this model. This allows customization of
+      # Defines or overrides an attribute on this model. This allows customization of
       # Active Record's type casting behavior, as well as adding support for user defined
       # types.
       #
@@ -75,65 +73,44 @@ module ActiveRecord
       #
       #   store_listing = StoreListing.new(price_in_cents: '$10.00')
       #   store_listing.price_in_cents # => 1000
-      def attribute(name, cast_type, options = {})
+      def attribute(name, cast_type, **options)
         name = name.to_s
-        clear_caches_calculated_from_columns
-        # Assign a new hash to ensure that subclasses do not share a hash
-        self.user_provided_columns = user_provided_columns.merge(name => cast_type)
+        reload_schema_from_cache
 
-        if options.key?(:default)
-          self.user_provided_defaults = user_provided_defaults.merge(name => options[:default])
-        end
-      end
-
-      # Returns an array of column objects for the table associated with this class.
-      def columns
-        @columns ||= add_user_provided_columns(connection.schema_cache.columns(table_name))
+        self.user_provided_types = user_provided_types.merge(name => [cast_type, options])
       end
 
-      # Returns a hash of column objects for the table associated with this class.
-      def columns_hash
-        @columns_hash ||= Hash[columns.map { |c| [c.name, c] }]
+      def define_attribute(
+        name,
+        cast_type,
+        default: NO_DEFAULT_PROVIDED,
+        user_provided_default: true
+      )
+        attribute_types[name] = cast_type
+        define_default_attribute(name, default, cast_type, from_user: user_provided_default)
       end
 
-      def reset_column_information # :nodoc:
+      def load_schema!
         super
-        clear_caches_calculated_from_columns
+        user_provided_types.each do |name, (type, options)|
+          define_attribute(name, type, **options)
+        end
       end
 
       private
 
-      def add_user_provided_columns(schema_columns)
-        existing_columns = schema_columns.map do |column|
-          new_type = user_provided_columns[column.name]
-          if new_type
-            column.with_type(new_type)
-          else
-            column
-          end
-        end
+      NO_DEFAULT_PROVIDED = Object.new # :nodoc:
+      private_constant :NO_DEFAULT_PROVIDED
 
-        existing_column_names = existing_columns.map(&:name)
-        new_columns = user_provided_columns.except(*existing_column_names).map do |(name, type)|
-          connection.new_column(name, nil, type)
+      def define_default_attribute(name, value, type, from_user:)
+        if value == NO_DEFAULT_PROVIDED
+          default_attribute = _default_attributes[name].with_type(type)
+        elsif from_user
+          default_attribute = Attribute.from_user(name, value, type)
+        else
+          default_attribute = Attribute.from_database(name, value, type)
         end
-
-        existing_columns + new_columns
-      end
-
-      def clear_caches_calculated_from_columns
-        @arel_table = nil
-        @attributes_builder = nil
-        @column_names = nil
-        @column_types = nil
-        @columns = nil
-        @columns_hash = nil
-        @content_columns = nil
-        @default_attributes = nil
-      end
-
-      def raw_default_values
-        super.merge(user_provided_defaults)
+        _default_attributes[name] = default_attribute
       end
     end
   end
diff --git a/activerecord/lib/active_record/autosave_association.rb b/activerecord/lib/active_record/autosave_association.rb
index c39b045a5e..0792d19c3e 100644
--- a/activerecord/lib/active_record/autosave_association.rb
+++ b/activerecord/lib/active_record/autosave_association.rb
@@ -177,10 +177,8 @@ module ActiveRecord
         # before actually defining them.
         def add_autosave_association_callbacks(reflection)
           save_method = :"autosave_associated_records_for_#{reflection.name}"
-          validation_method = :"validate_associated_records_for_#{reflection.name}"
-          collection = reflection.collection?
 
-          if collection
+          if reflection.collection?
             before_save :before_save_collection_association
 
             define_non_cyclic_method(save_method) { save_collection_association(reflection) }
@@ -200,13 +198,29 @@ module ActiveRecord
             after_create save_method
             after_update save_method
           else
-            define_non_cyclic_method(save_method) { save_belongs_to_association(reflection) }
+            define_non_cyclic_method(save_method) { throw(:abort) if save_belongs_to_association(reflection) == false }
             before_save save_method
           end
 
+          define_autosave_validation_callbacks(reflection)
+        end
+
+        def define_autosave_validation_callbacks(reflection)
+          validation_method = :"validate_associated_records_for_#{reflection.name}"
           if reflection.validate? && !method_defined?(validation_method)
-            method = (collection ? :validate_collection_association : :validate_single_association)
-            define_non_cyclic_method(validation_method) { send(method, reflection) }
+            if reflection.collection?
+              method = :validate_collection_association
+            else
+              method = :validate_single_association
+            end
+
+            define_non_cyclic_method(validation_method) do
+              send(method, reflection)
+              # TODO: remove the following line as soon as the return value of
+              # callbacks is ignored, that is, returning `false` does not
+              # display a deprecation warning or halts the callback chain.
+              true
+            end
             validate validation_method
           end
         end
@@ -272,11 +286,18 @@ module ActiveRecord
       # go through nested autosave associations that are loaded in memory (without loading
       # any new ones), and return true if is changed for autosave
       def nested_records_changed_for_autosave?
-        self.class._reflections.values.any? do |reflection|
-          if reflection.options[:autosave]
-            association = association_instance_get(reflection.name)
-            association && Array.wrap(association.target).any?(&:changed_for_autosave?)
+        @_nested_records_changed_for_autosave_already_called ||= false
+        return false if @_nested_records_changed_for_autosave_already_called
+        begin
+          @_nested_records_changed_for_autosave_already_called = true
+          self.class._reflections.values.any? do |reflection|
+            if reflection.options[:autosave]
+              association = association_instance_get(reflection.name)
+              association && Array.wrap(association.target).any?(&:changed_for_autosave?)
+            end
           end
+        ensure
+          @_nested_records_changed_for_autosave_already_called = false
         end
       end
 
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index bb01231bca..100d3780f6 100644
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -312,6 +312,7 @@ module ActiveRecord #:nodoc:
     include Reflection
     include Serialization
     include Store
+    include SecureToken
   end
 
   ActiveSupport.run_load_hooks(:active_record, Base)
diff --git a/activerecord/lib/active_record/callbacks.rb b/activerecord/lib/active_record/callbacks.rb
index 497ce8c15c..f44e5af5de 100644
--- a/activerecord/lib/active_record/callbacks.rb
+++ b/activerecord/lib/active_record/callbacks.rb
@@ -192,14 +192,14 @@ module ActiveRecord
   #
   # == <tt>before_validation*</tt> returning statements
   #
-  # If the returning value of a +before_validation+ callback can be evaluated to +false+, the process will be
+  # If the +before_validation+ callback throws +:abort+, the process will be
   # aborted and <tt>Base#save</tt> will return +false+. If Base#save! is called it will raise a
   # ActiveRecord::RecordInvalid exception. Nothing will be appended to the errors object.
   #
   # == Canceling callbacks
   #
-  # If a <tt>before_*</tt> callback returns +false+, all the later callbacks and the associated action are
-  # cancelled. If an <tt>after_*</tt> callback returns +false+, all the later callbacks are cancelled.
+  # If a <tt>before_*</tt> callback throws +:abort+, all the later callbacks and
+  # the associated action are cancelled.
   # Callbacks are generally run in the order they are defined, with the exception of callbacks defined as
   # methods on the model, which are called last.
   #
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
index 6235745fb2..d99dc9a5db 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
@@ -2,7 +2,6 @@ require 'thread'
 require 'thread_safe'
 require 'monitor'
 require 'set'
-require 'active_support/core_ext/string/filters'
 
 module ActiveRecord
   # Raised when a connection could not be obtained within the connection
@@ -454,6 +453,10 @@ module ActiveRecord
           c.verify!
         end
         c
+      rescue
+        remove c
+        c.disconnect!
+        raise
       end
     end
 
@@ -517,15 +520,7 @@ module ActiveRecord
       def connection_pool_list
         owner_to_pool.values.compact
       end
-
-      def connection_pools
-        ActiveSupport::Deprecation.warn(<<-MSG.squish)
-          In the next release, this will return the same as `#connection_pool_list`.
-          (An array of pools, rather than a hash mapping specs to pools.)
-        MSG
-
-        Hash[connection_pool_list.map { |pool| [pool.spec, pool] }]
-      end
+      alias :connection_pools :connection_pool_list
 
       def establish_connection(owner, spec)
         @class_to_pool.clear
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 59cdd8e98c..c3e5e9ad61 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
@@ -285,10 +285,17 @@ module ActiveRecord
       def insert_fixture(fixture, table_name)
         columns = schema_cache.columns_hash(table_name)
 
-        key_list   = []
-        value_list = fixture.map do |name, value|
-          key_list << quote_column_name(name)
-          quote(value, columns[name])
+        binds = fixture.map do |name, value|
+          type = lookup_cast_type_from_column(columns[name])
+          Relation::QueryAttribute.new(name, value, type)
+        end
+        key_list = fixture.keys.map { |name| quote_column_name(name) }
+        value_list = prepare_binds_for_database(binds).map do |value|
+          begin
+            quote(value)
+          rescue TypeError
+            quote(YAML.dump(value))
+          end
         end
 
         execute "INSERT INTO #{quote_table_name(table_name)} (#{key_list.join(', ')}) VALUES (#{value_list.join(', ')})", 'Fixture Insert'
@@ -375,7 +382,7 @@ module ActiveRecord
 
         def binds_from_relation(relation, binds)
           if relation.is_a?(Relation) && binds.empty?
-            relation, binds = relation.arel, relation.bind_values
+            relation, binds = relation.arel, relation.bound_attributes
           end
           [relation, binds]
         end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb b/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb
index 143d7d9574..2456376d6d 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb
@@ -10,7 +10,13 @@ module ActiveRecord
         return value.quoted_id if value.respond_to?(:quoted_id)
 
         if column
-          value = column.cast_type.type_cast_for_database(value)
+          ActiveSupport::Deprecation.warn(<<-MSG.squish)
+            Passing a column to `quote` has been deprecated. It is only used
+            for type casting, which should be handled elsewhere. See
+            https://github.com/rails/arel/commit/6160bfbda1d1781c3b08a33ec4955f170e95be11
+            for more information.
+          MSG
+          value = type_cast_from_column(column, value)
         end
 
         _quote(value)
@@ -25,7 +31,7 @@ module ActiveRecord
         end
 
         if column
-          value = column.cast_type.type_cast_for_database(value)
+          value = type_cast_from_column(column, value)
         end
 
         _type_cast(value)
@@ -34,6 +40,29 @@ module ActiveRecord
         raise TypeError, "can't cast #{value.class}#{to_type}"
       end
 
+      # If you are having to call this function, you are likely doing something
+      # wrong. The column does not have sufficient type information if the user
+      # provided a custom type on the class level either explicitly (via
+      # `attribute`) or implicitly (via `serialize`,
+      # `time_zone_aware_attributes`). In almost all cases, the sql type should
+      # only be used to change quoting behavior, when the primitive to
+      # represent the type doesn't sufficiently reflect the differences
+      # (varchar vs binary) for example. The type used to get this primitive
+      # should have been provided before reaching the connection adapter.
+      def type_cast_from_column(column, value) # :nodoc:
+        if column
+          type = lookup_cast_type_from_column(column)
+          type.type_cast_for_database(value)
+        else
+          value
+        end
+      end
+
+      # See docs for +type_cast_from_column+
+      def lookup_cast_type_from_column(column) # :nodoc:
+        lookup_cast_type(column.sql_type)
+      end
+
       # Quotes a string, escaping any ' (single quote) and \ (backslash)
       # characters.
       def quote_string(s)
@@ -90,6 +119,10 @@ module ActiveRecord
         value.to_s(:db)
       end
 
+      def prepare_binds_for_database(binds) # :nodoc:
+        binds.map(&:value_for_database)
+      end
+
       private
 
       def types_which_need_no_typecasting
@@ -109,8 +142,7 @@ module ActiveRecord
         when Date, Time then "'#{quoted_date(value)}'"
         when Symbol     then "'#{quote_string(value.to_s)}'"
         when Class      then "'#{value}'"
-        else
-          "'#{quote_string(YAML.dump(value))}'"
+        else raise TypeError, "can't quote #{value.class.name}"
         end
       end
 
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb
index 18ff869ea6..db20b60d60 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb
@@ -28,8 +28,8 @@ module ActiveRecord
           end
 
           def visit_ColumnDefinition(o)
-            sql_type = type_to_sql(o.type, o.limit, o.precision, o.scale)
-            column_sql = "#{quote_column_name(o.name)} #{sql_type}"
+            o.sql_type = type_to_sql(o.type, o.limit, o.precision, o.scale)
+            column_sql = "#{quote_column_name(o.name)} #{o.sql_type}"
             add_column_options!(column_sql, column_options(o)) unless o.type == :primary_key
             column_sql
           end
@@ -98,9 +98,7 @@ module ActiveRecord
           end
 
           def quote_default_expression(value, column)
-            column.sql_type ||= type_to_sql(column.type, column.limit, column.precision, column.scale)
             value = type_for_column(column).type_cast_for_database(value)
-
             @conn.quote(value)
           end
 
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 68d8a2cd6a..7eaa89c9a7 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
@@ -56,18 +56,6 @@ module ActiveRecord
       end
     end
 
-    module TimestampDefaultDeprecation # :nodoc:
-      def emit_warning_if_null_unspecified(options)
-        return if options.key?(:null)
-
-        ActiveSupport::Deprecation.warn(<<-MSG.squish)
-          `#timestamp` was called without specifying an option for `null`. In Rails 5,
-          this behavior will change to `null: false`. You should manually specify
-         `null: true` to prevent the behavior of your existing migrations from changing.
-        MSG
-      end
-    end
-
     class ReferenceDefinition # :nodoc:
       def initialize(
         name,
@@ -167,8 +155,6 @@ module ActiveRecord
     # The table definitions
     # The Columns are stored as a ColumnDefinition in the +columns+ attribute.
     class TableDefinition
-      include TimestampDefaultDeprecation
-
       # An array of ColumnDefinition objects, representing the column changes
       # that have been defined.
       attr_accessor :indexes
@@ -375,7 +361,9 @@ module ActiveRecord
       #   t.timestamps null: false
       def timestamps(*args)
         options = args.extract_options!
-        emit_warning_if_null_unspecified(options)
+
+        options[:null] = false if options[:null].nil?
+
         column(:created_at, :datetime, options)
         column(:updated_at, :datetime, options)
       end
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 42ea599a74..932aaf7aa7 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb
@@ -46,9 +46,10 @@ module ActiveRecord
       private
 
       def schema_default(column)
-        default = column.type_cast_from_database(column.default)
+        type = lookup_cast_type_from_column(column)
+        default = type.type_cast_from_database(column.default)
         unless default.nil?
-          column.type_cast_for_schema(default)
+          type.type_cast_for_schema(default)
         end
       end
     end
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 34d60493ea..f905669a24 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -380,7 +380,7 @@ module ActiveRecord
       # it can be helpful to provide these in a migration's +change+ method so it can be reverted.
       # In that case, +options+ and the block will be used by create_table.
       def drop_table(table_name, options = {})
-        execute "DROP TABLE #{quote_table_name(table_name)}"
+        execute "DROP TABLE#{' IF EXISTS' if options[:if_exists]} #{quote_table_name(table_name)}"
       end
 
       # Adds a new column to the named table.
@@ -851,14 +851,14 @@ module ActiveRecord
         columns
       end
 
-      include TimestampDefaultDeprecation
       # Adds timestamps (+created_at+ and +updated_at+) columns to +table_name+.
       # Additional options (like <tt>null: false</tt>) are forwarded to #add_column.
       #
       #   add_timestamps(:suppliers, null: false)
       #
       def add_timestamps(table_name, options = {})
-        emit_warning_if_null_unspecified(options)
+        options[:null] = false if options[:null].nil?
+
         add_column table_name, :created_at, :datetime, options
         add_column table_name, :updated_at, :datetime, options
       end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb b/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb
index fd666c8c39..7f738e89c9 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb
@@ -69,16 +69,11 @@ module ActiveRecord
       def rollback_records
         ite = records.uniq
         while record = ite.shift
-          begin
-            record.rolledback! full_rollback?
-          rescue => e
-            raise if ActiveRecord::Base.raise_in_transactional_callbacks
-            record.logger.error(e) if record.respond_to?(:logger) && record.logger
-          end
+          record.rolledback!(force_restore_state: full_rollback?)
         end
       ensure
         ite.each do |i|
-          i.rolledback!(full_rollback?, false)
+          i.rolledback!(force_restore_state: full_rollback?, should_run_callbacks: false)
         end
       end
 
@@ -89,16 +84,11 @@ module ActiveRecord
       def commit_records
         ite = records.uniq
         while record = ite.shift
-          begin
-            record.committed!
-          rescue => e
-            raise if ActiveRecord::Base.raise_in_transactional_callbacks
-            record.logger.error(e) if record.respond_to?(:logger) && record.logger
-          end
+          record.committed!
         end
       ensure
         ite.each do |i|
-          i.committed!(false)
+          i.committed!(should_run_callbacks: false)
         end
       end
 
@@ -121,14 +111,11 @@ module ActiveRecord
       def rollback
         connection.rollback_to_savepoint(savepoint_name)
         super
-        rollback_records
       end
 
       def commit
         connection.release_savepoint(savepoint_name)
         super
-        parent = connection.transaction_manager.current_transaction
-        records.each { |r| parent.add_record(r) }
       end
 
       def full_rollback?; false; end
@@ -148,13 +135,11 @@ module ActiveRecord
       def rollback
         connection.rollback_db_transaction
         super
-        rollback_records
       end
 
       def commit
         connection.commit_db_transaction
         super
-        commit_records
       end
     end
 
@@ -171,16 +156,28 @@ module ActiveRecord
           else
             SavepointTransaction.new(@connection, "active_record_#{@stack.size}", options)
           end
+
         @stack.push(transaction)
         transaction
       end
 
       def commit_transaction
-        @stack.pop.commit
+        inner_transaction = @stack.pop
+        inner_transaction.commit
+
+        if current_transaction.joinable?
+          inner_transaction.records.each do |r|
+            current_transaction.add_record(r)
+          end
+        else
+          inner_transaction.commit_records
+        end
       end
 
-      def rollback_transaction
-        @stack.pop.rollback
+      def rollback_transaction(transaction = nil)
+        transaction ||= @stack.pop
+        transaction.rollback
+        transaction.rollback_records
       end
 
       def within_new_transaction(options = {})
@@ -197,7 +194,7 @@ module ActiveRecord
             begin
               commit_transaction
             rescue Exception
-              transaction.rollback unless transaction.state.completed?
+              rollback_transaction(transaction) unless transaction.state.completed?
               raise
             end
           end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index fa24d9b43f..436552d300 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -25,7 +25,6 @@ module ActiveRecord
       autoload :TableDefinition
       autoload :Table
       autoload :AlterTable
-      autoload :TimestampDefaultDeprecation
     end
 
     autoload_at 'active_record/connection_adapters/abstract/connection_pool' do
@@ -114,7 +113,8 @@ module ActiveRecord
 
       class BindCollector < Arel::Collectors::Bind
         def compile(bvs, conn)
-          super(bvs.map { |bv| conn.quote(*bv.reverse) })
+          casted_binds = conn.prepare_binds_for_database(bvs)
+          super(casted_binds.map { |value| conn.quote(value) })
         end
       end
 
@@ -393,7 +393,7 @@ module ActiveRecord
       end
 
       def column_name_for_operation(operation, node) # :nodoc:
-        node.to_sql
+        visitor.accept(node, collector).value
       end
 
       protected
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 e9a3c26c32..b61b717a61 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -502,7 +502,7 @@ module ActiveRecord
       end
 
       def drop_table(table_name, options = {})
-        execute "DROP#{' TEMPORARY' if options[:temporary]} TABLE #{quote_table_name(table_name)}#{' CASCADE' if options[:force] == :cascade}"
+        execute "DROP#{' TEMPORARY' if options[:temporary]} TABLE#{' IF EXISTS' if options[:if_exists]} #{quote_table_name(table_name)}#{' CASCADE' if options[:force] == :cascade}"
       end
 
       def rename_index(table_name, old_name, new_name)
diff --git a/activerecord/lib/active_record/connection_adapters/column.rb b/activerecord/lib/active_record/connection_adapters/column.rb
index af307b57a4..a489141d1a 100644
--- a/activerecord/lib/active_record/connection_adapters/column.rb
+++ b/activerecord/lib/active_record/connection_adapters/column.rb
@@ -5,7 +5,6 @@ module ActiveRecord
   module ConnectionAdapters
     # An abstract definition of a column in a table.
     class Column
-      TRUE_VALUES = [true, 1, '1', 't', 'T', 'true', 'TRUE', 'on', 'ON'].to_set
       FALSE_VALUES = [false, 0, '0', 'f', 'F', 'false', 'FALSE', 'off', 'OFF'].to_set
 
       module Format
@@ -15,11 +14,7 @@ module ActiveRecord
 
       attr_reader :name, :cast_type, :null, :sql_type, :default, :default_function
 
-      delegate :type, :precision, :scale, :limit, :klass, :accessor,
-        :text?, :number?, :binary?, :changed?,
-        :type_cast_from_user, :type_cast_from_database, :type_cast_for_database,
-        :type_cast_for_schema,
-        to: :cast_type
+      delegate :precision, :scale, :limit, :type, to: :cast_type
 
       # Instantiates a new column in the table.
       #
@@ -30,13 +25,13 @@ module ActiveRecord
       # <tt>company_name varchar(60)</tt>.
       # It will be mapped to one of the standard Rails SQL types in the <tt>type</tt> attribute.
       # +null+ determines if this column allows +NULL+ values.
-      def initialize(name, default, cast_type, sql_type = nil, null = true)
+      def initialize(name, default, cast_type, sql_type = nil, null = true, default_function = nil)
         @name             = name
         @cast_type        = cast_type
         @sql_type         = sql_type
         @null             = null
         @default          = default
-        @default_function = nil
+        @default_function = default_function
       end
 
       def has_default?
@@ -77,6 +72,12 @@ module ActiveRecord
         [self.class, name, default, cast_type, sql_type, null, default_function]
       end
     end
+
+    class NullColumn < Column
+      def initialize(name)
+        super name, nil, Type::Value.new
+      end
+    end
   end
   # :startdoc:
 end
diff --git a/activerecord/lib/active_record/connection_adapters/connection_specification.rb b/activerecord/lib/active_record/connection_adapters/connection_specification.rb
index e54e3199ff..08d46fca96 100644
--- a/activerecord/lib/active_record/connection_adapters/connection_specification.rb
+++ b/activerecord/lib/active_record/connection_adapters/connection_specification.rb
@@ -1,5 +1,4 @@
 require 'uri'
-require 'active_support/core_ext/string/filters'
 
 module ActiveRecord
   module ConnectionAdapters
@@ -210,30 +209,12 @@ module ActiveRecord
           when Symbol
             resolve_symbol_connection spec
           when String
-            resolve_string_connection spec
+            resolve_url_connection spec
           when Hash
             resolve_hash_connection spec
           end
         end
 
-        def resolve_string_connection(spec)
-          # Rails has historically accepted a string to mean either
-          # an environment key or a URL spec, so we have deprecated
-          # this ambiguous behaviour and in the future this function
-          # can be removed in favor of resolve_url_connection.
-          if configurations.key?(spec) || spec !~ /:/
-            ActiveSupport::Deprecation.warn(<<-MSG.squish)
-              Passing a string to ActiveRecord::Base.establish_connection for a
-              configuration lookup is deprecated, please pass a symbol
-              (#{spec.to_sym.inspect}) instead.
-            MSG
-
-            resolve_symbol_connection(spec)
-          else
-            resolve_url_connection(spec)
-          end
-        end
-
         # Takes the environment such as +:production+ or +:development+.
         # This requires that the @configurations was initialized with a key that
         # matches.
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index 23d8389abb..16f50fc594 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -395,11 +395,9 @@ module ActiveRecord
 
       def exec_stmt(sql, name, binds)
         cache = {}
-        type_casted_binds = binds.map { |col, val|
-          [col, type_cast(val, col)]
-        }
+        type_casted_binds = binds.map { |attr| type_cast(attr.value_for_database) }
 
-        log(sql, name, type_casted_binds) do
+        log(sql, name, binds) do
           if binds.empty?
             stmt = @connection.prepare(sql)
           else
@@ -410,7 +408,7 @@ module ActiveRecord
           end
 
           begin
-            stmt.execute(*type_casted_binds.map { |_, val| val })
+            stmt.execute(*type_casted_binds)
           rescue Mysql::Error => e
             # Older versions of MySQL leave the prepared statement in a bad
             # place when an error occurs. To support older MySQL versions, we
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/column.rb b/activerecord/lib/active_record/connection_adapters/postgresql/column.rb
index 1458fbf496..8f3628ec0e 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/column.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/column.rb
@@ -2,18 +2,19 @@ module ActiveRecord
   module ConnectionAdapters
     # PostgreSQL-specific extensions to column definitions in a table.
     class PostgreSQLColumn < Column #:nodoc:
-      attr_accessor :array
+      attr_reader :array, :oid, :fmod
+      alias :array? :array
 
-      def initialize(name, default, cast_type, sql_type = nil, null = true, default_function = nil)
+      def initialize(name, default, cast_type, sql_type = nil, null = true, default_function = nil, oid = nil, fmod = nil)
         if sql_type =~ /\[\]$/
           @array = true
-          super(name, default, cast_type, sql_type[0..sql_type.length - 3], null)
+          sql_type = sql_type[0..sql_type.length - 3]
         else
           @array = false
-          super(name, default, cast_type, sql_type, null)
         end
-
-        @default_function = default_function
+        @oid = oid
+        @fmod = fmod
+        super(name, default, cast_type, sql_type, null, default_function)
       end
 
       def serial?
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb
index c203e6c604..e45a2f59d9 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb
@@ -18,7 +18,7 @@ module ActiveRecord
           end
 
           attr_reader :subtype, :delimiter
-          delegate :type, to: :subtype
+          delegate :type, :user_input_in_time_zone, to: :subtype
 
           def initialize(subtype, delimiter = ',')
             @subtype = subtype
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb
index e12ddd9901..7dadc09a44 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb
@@ -11,7 +11,7 @@ module ActiveRecord
 
           def type_cast_from_database(value)
             if value.is_a?(::String)
-              ::ActiveSupport::JSON.decode(value)
+              ::ActiveSupport::JSON.decode(value) rescue nil
             else
               super
             end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/range.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/range.rb
index 961e6224c4..3adfb8b9d8 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/range.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/range.rb
@@ -25,16 +25,7 @@ module ActiveRecord
             to = type_cast_single extracted[:to]
 
             if !infinity?(from) && extracted[:exclude_start]
-              if from.respond_to?(:succ)
-                from = from.succ
-                ActiveSupport::Deprecation.warn(<<-MSG.squish)
-                  Excluding the beginning of a Range is only partialy supported
-                  through `#succ`. This is not reliable and will be removed in
-                  the future.
-                MSG
-              else
-                raise ArgumentError, "The Ruby Range object does not support excluding the beginning of a Range. (unsupported value: '#{value}')"
-              end
+              raise ArgumentError, "The Ruby Range object does not support excluding the beginning of a Range. (unsupported value: '#{value}')"
             end
             ::Range.new(from, to, extracted[:exclude_end])
           end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb b/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb
index 607848884b..464adb4e23 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb
@@ -56,10 +56,15 @@ module ActiveRecord
           if column.type == :uuid && value =~ /\(\)/
             value
           else
-            quote(value, column)
+            value = type_cast_from_column(column, value)
+            quote(value)
           end
         end
 
+        def lookup_cast_type_from_column(column) # :nodoc:
+          type_map.lookup(column.oid, column.fmod, column.sql_type)
+        end
+
         private
 
         def _quote(value)
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
index a90adcf4aa..519a9727fb 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
@@ -112,7 +112,7 @@ module ActiveRecord
         end
 
         def drop_table(table_name, options = {})
-          execute "DROP TABLE #{quote_table_name(table_name)}#{' CASCADE' if options[:force] == :cascade}"
+          execute "DROP TABLE#{' IF EXISTS' if options[:if_exists]} #{quote_table_name(table_name)}#{' CASCADE' if options[:force] == :cascade}"
         end
 
         # Returns true if schema exists.
@@ -183,15 +183,17 @@ module ActiveRecord
         def columns(table_name)
           # Limit, precision, and scale are all handled by the superclass.
           column_definitions(table_name).map do |column_name, type, default, notnull, oid, fmod|
-            oid = get_oid_type(oid.to_i, fmod.to_i, column_name, type)
-            default_value = extract_value_from_default(oid, default)
+            oid = oid.to_i
+            fmod = fmod.to_i
+            cast_type = get_oid_type(oid, fmod, column_name, type)
+            default_value = extract_value_from_default(cast_type, default)
             default_function = extract_default_function(default_value, default)
-            new_column(column_name, default_value, oid, type, notnull == 'f', default_function)
+            new_column(column_name, default_value, cast_type, type, notnull == 'f', default_function, oid, fmod)
           end
         end
 
-        def new_column(name, default, cast_type, sql_type = nil, null = true, default_function = nil) # :nodoc:
-          PostgreSQLColumn.new(name, default, cast_type, sql_type, null, default_function)
+        def new_column(name, default, cast_type, sql_type = nil, null = true, default_function = nil, oid = nil, fmod = nil) # :nodoc:
+          PostgreSQLColumn.new(name, default, cast_type, sql_type, null, default_function, oid, fmod)
         end
 
         # Returns the current database name.
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 13bb5c187e..d789069f0b 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -64,7 +64,7 @@ module ActiveRecord
     #   <tt>SET client_min_messages TO <min_messages></tt> call on the connection.
     # * <tt>:variables</tt> - An optional hash of additional parameters that
     #   will be used in <tt>SET SESSION key = val</tt> calls on the connection.
-    # * <tt>:insert_returning</tt> - An optional boolean to control the use or <tt>RETURNING</tt> for <tt>INSERT</tt> statements
+    # * <tt>:insert_returning</tt> - An optional boolean to control the use of <tt>RETURNING</tt> for <tt>INSERT</tt> statements
     #   defaults to true.
     #
     # Any further options are used as connection parameters to libpq. See
@@ -144,7 +144,7 @@ module ActiveRecord
       # AbstractAdapter
       def prepare_column_options(column) # :nodoc:
         spec = super
-        spec[:array] = 'true' if column.respond_to?(:array) && column.array
+        spec[:array] = 'true' if column.array?
         spec[:default] = "\"#{column.default_function}\"" if column.default_function
         spec
       end
@@ -609,12 +609,10 @@ module ActiveRecord
 
         def exec_cache(sql, name, binds)
           stmt_key = prepare_statement(sql)
-          type_casted_binds = binds.map { |col, val|
-            [col, type_cast(val, col)]
-          }
+          type_casted_binds = binds.map { |attr| type_cast(attr.value_for_database) }
 
-          log(sql, name, type_casted_binds, stmt_key) do
-            @connection.exec_prepared(stmt_key, type_casted_binds.map { |_, val| val })
+          log(sql, name, binds, stmt_key) do
+            @connection.exec_prepared(stmt_key, type_casted_binds)
           end
         rescue ActiveRecord::StatementInvalid => e
           pgerror = e.original_exception
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
index 03dfd29a0a..02a3b65934 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
@@ -50,16 +50,6 @@ module ActiveRecord
       end
     end
 
-    class SQLite3String < Type::String # :nodoc:
-      def type_cast_for_database(value)
-        if value.is_a?(::String) && value.encoding == Encoding::ASCII_8BIT
-          value.encode(Encoding::UTF_8)
-        else
-          super
-        end
-      end
-    end
-
     # The SQLite3 adapter works SQLite 3.6.16 or newer
     # with the sqlite3-ruby drivers (available as gem from https://rubygems.org/gems/sqlite3).
     #
@@ -239,6 +229,12 @@ module ActiveRecord
         case value
         when BigDecimal
           value.to_f
+        when String
+          if value.encoding == Encoding::ASCII_8BIT
+            super(value.encode(Encoding::UTF_8))
+          else
+            super
+          end
         else
           super
         end
@@ -280,11 +276,9 @@ module ActiveRecord
       end
 
       def exec_query(sql, name = nil, binds = [])
-        type_casted_binds = binds.map { |col, val|
-          [col, type_cast(val, col)]
-        }
+        type_casted_binds = binds.map { |attr| type_cast(attr.value_for_database) }
 
-        log(sql, name, type_casted_binds) do
+        log(sql, name, binds) do
           # Don't cache statements if they are not prepared
           if without_prepared_statement?(binds)
             stmt    = @connection.prepare(sql)
@@ -302,7 +296,7 @@ module ActiveRecord
             stmt = cache[:stmt]
             cols = cache[:cols] ||= stmt.columns
             stmt.reset!
-            stmt.bind_params type_casted_binds.map { |_, val| val }
+            stmt.bind_params type_casted_binds
           end
 
           ActiveRecord::Result.new(cols, stmt.to_a)
@@ -498,7 +492,6 @@ module ActiveRecord
         def initialize_type_map(m)
           super
           m.register_type(/binary/i, SQLite3Binary.new)
-          register_class_with_limit m, %r(char)i, SQLite3String
         end
 
         def table_structure(table_name)
diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index 38b2d632d2..4416217897 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -87,13 +87,6 @@ module ActiveRecord
 
       mattr_accessor :maintain_test_schema, instance_accessor: false
 
-      def self.disable_implicit_join_references=(value)
-        ActiveSupport::Deprecation.warn(<<-MSG.squish)
-          Implicit join references were removed with Rails 4.1.
-          Make sure to remove this configuration because it does nothing.
-        MSG
-      end
-
       class_attribute :default_connection_handler, instance_writer: false
       class_attribute :find_by_statement_cache
 
@@ -217,7 +210,7 @@ module ActiveRecord
         elsif !connected?
           "#{super} (call '#{super}.connection' to establish a connection)"
         elsif table_exists?
-          attr_list = columns.map { |c| "#{c.name}: #{c.type}" } * ', '
+          attr_list = attribute_types.map { |name, type| "#{name}: #{type.type}" } * ', '
           "#{super}(#{attr_list})"
         else
           "#{super}(Table doesn't exist)"
@@ -281,16 +274,14 @@ module ActiveRecord
     # ==== Example:
     #   # Instantiates a single new object
     #   User.new(first_name: 'Jamie')
-    def initialize(attributes = nil, options = {})
+    def initialize(attributes = nil)
       @attributes = self.class._default_attributes.dup
+      self.class.define_attribute_methods
 
       init_internals
       initialize_internals_callback
 
-      self.class.define_attribute_methods
-      # +options+ argument is only needed to make protected_attributes gem easier to hook.
-      # Remove it when we drop support to this gem.
-      init_attributes(attributes, options) if attributes
+      assign_attributes(attributes) if attributes
 
       yield self if block_given?
       _run_initialize_callbacks
@@ -465,6 +456,7 @@ module ActiveRecord
     # Takes a PP and prettily prints this record to it, allowing you to get a nice result from `pp record`
     # when pp is required.
     def pretty_print(pp)
+      return super if custom_inspect_method_defined?
       pp.object_address_group(self) do
         if defined?(@attributes) && @attributes
           column_names = self.class.column_names.select { |name| has_attribute?(name) || new_record? }
@@ -564,16 +556,14 @@ module ActiveRecord
     def initialize_internals_callback
     end
 
-    # This method is needed to make protected_attributes gem easier to hook.
-    # Remove it when we drop support to this gem.
-    def init_attributes(attributes, options)
-      assign_attributes(attributes)
-    end
-
     def thaw
       if frozen?
         @attributes = @attributes.dup
       end
     end
+
+    def custom_inspect_method_defined?
+      self.class.instance_method(:inspect).owner != ActiveRecord::Base.instance_method(:inspect).owner
+    end
   end
 end
diff --git a/activerecord/lib/active_record/counter_cache.rb b/activerecord/lib/active_record/counter_cache.rb
index 7d8e0a2063..82596b63df 100644
--- a/activerecord/lib/active_record/counter_cache.rb
+++ b/activerecord/lib/active_record/counter_cache.rb
@@ -156,7 +156,7 @@ module ActiveRecord
 
       def each_counter_cached_associations
         _reflections.each do |name, reflection|
-          yield association(name) if reflection.belongs_to? && reflection.counter_cache_column
+          yield association(name.to_sym) if reflection.belongs_to? && reflection.counter_cache_column
         end
       end
 
diff --git a/activerecord/lib/active_record/errors.rb b/activerecord/lib/active_record/errors.rb
index fc28ab585f..d710d96a9a 100644
--- a/activerecord/lib/active_record/errors.rb
+++ b/activerecord/lib/active_record/errors.rb
@@ -178,18 +178,10 @@ module ActiveRecord
   class DangerousAttributeError < ActiveRecordError
   end
 
-  # Raised when unknown attributes are supplied via mass assignment.
-  class UnknownAttributeError < NoMethodError
-
-    attr_reader :record, :attribute
-
-    def initialize(record, attribute)
-      @record = record
-      @attribute = attribute.to_s
-      super("unknown attribute '#{attribute}' for #{@record.class}.")
-    end
-
-  end
+  UnknownAttributeError = ActiveSupport::Deprecation::DeprecatedConstantProxy.new( # :nodoc:
+    'ActiveRecord::UnknownAttributeError', 
+    'ActiveModel::AttributeAssignment::UnknownAttributeError'
+  )
 
   # Raised when an error occurred while doing a mass assignment to an attribute through the
   # +attributes=+ method. The exception has an +attribute+ property that is the name of the
diff --git a/activerecord/lib/active_record/fixtures.rb b/activerecord/lib/active_record/fixtures.rb
index 4732462b05..57db2faaff 100644
--- a/activerecord/lib/active_record/fixtures.rb
+++ b/activerecord/lib/active_record/fixtures.rb
@@ -1,6 +1,7 @@
 require 'erb'
 require 'yaml'
 require 'zlib'
+require 'set'
 require 'active_support/dependencies'
 require 'active_support/core_ext/digest/uuid'
 require 'active_record/fixture_set/file'
@@ -521,12 +522,16 @@ module ActiveRecord
           update_all_loaded_fixtures fixtures_map
 
           connection.transaction(:requires_new => true) do
+            deleted_tables = 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|
-                conn.delete "DELETE FROM #{conn.quote_table_name(table)}", 'Fixture Delete'
+                unless deleted_tables.include? table
+                  conn.delete "DELETE FROM #{conn.quote_table_name(table)}", 'Fixture Delete'
+                end
+                deleted_tables << table
               end
 
               table_rows.each do |fixture_set_name, rows|
@@ -633,7 +638,7 @@ module ActiveRecord
 
           # interpolate the fixture label
           row.each do |key, value|
-            row[key] = value.gsub("$LABEL", label) if value.is_a?(String)
+            row[key] = value.gsub("$LABEL", label.to_s) if value.is_a?(String)
           end
 
           # generate a primary key if necessary
@@ -661,7 +666,7 @@ module ActiveRecord
                   row[association.foreign_type] = $1
                 end
 
-                fk_type = association.active_record.columns_hash[fk_name].type
+                fk_type = association.active_record.type_for_attribute(fk_name).type
                 row[fk_name] = ActiveRecord::FixtureSet.identify(value, fk_type)
               end
             when :has_many
@@ -691,7 +696,7 @@ module ActiveRecord
       end
 
       def primary_key_type
-        @association.klass.column_types[@association.klass.primary_key].type
+        @association.klass.type_for_attribute(@association.klass.primary_key).type
       end
     end
 
@@ -711,7 +716,7 @@ module ActiveRecord
       end
 
       def primary_key_type
-        @primary_key_type ||= model_class && model_class.column_types[model_class.primary_key].type
+        @primary_key_type ||= model_class && model_class.type_for_attribute(model_class.primary_key).type
       end
 
       def add_join_records(rows, row, association)
@@ -768,12 +773,6 @@ module ActiveRecord
 
   end
 
-  #--
-  # Deprecate 'Fixtures' in favor of 'FixtureSet'.
-  #++
-  # :nodoc:
-  Fixtures = ActiveSupport::Deprecation::DeprecatedConstantProxy.new('ActiveRecord::Fixtures', 'ActiveRecord::FixtureSet')
-
   class Fixture #:nodoc:
     include Enumerable
 
@@ -888,7 +887,7 @@ module ActiveRecord
               @fixture_cache[fs_name] ||= {}
 
               instances = fixture_names.map do |f_name|
-                f_name = f_name.to_s
+                f_name = f_name.to_s if f_name.is_a?(Symbol)
                 @fixture_cache[fs_name].delete(f_name) if force_reload
 
                 if @loaded_fixtures[fs_name][f_name]
diff --git a/activerecord/lib/active_record/inheritance.rb b/activerecord/lib/active_record/inheritance.rb
index b91e9ac137..24098f72dc 100644
--- a/activerecord/lib/active_record/inheritance.rb
+++ b/activerecord/lib/active_record/inheritance.rb
@@ -79,16 +79,6 @@ module ActiveRecord
         :true == (@finder_needs_type_condition ||= descends_from_active_record? ? :false : :true)
       end
 
-      def symbolized_base_class
-        ActiveSupport::Deprecation.warn('`ActiveRecord::Base.symbolized_base_class` is deprecated and will be removed without replacement.')
-        @symbolized_base_class ||= base_class.to_s.to_sym
-      end
-
-      def symbolized_sti_name
-        ActiveSupport::Deprecation.warn('`ActiveRecord::Base.symbolized_sti_name` is deprecated and will be removed without replacement.')
-        @symbolized_sti_name ||= sti_name.present? ? sti_name.to_sym : symbolized_base_class
-      end
-
       # Returns the class descending directly from ActiveRecord::Base, or
       # an abstract class, if any, in the inheritance hierarchy.
       #
@@ -202,7 +192,7 @@ module ActiveRecord
       # If this is a StrongParameters hash, and access to inheritance_column is not permitted,
       # this will ignore the inheritance column and return nil
       def subclass_from_attributes?(attrs)
-        columns_hash.include?(inheritance_column) && attrs.is_a?(Hash)
+        attribute_names.include?(inheritance_column) && attrs.is_a?(Hash)
       end
 
       def subclass_from_attributes(attrs)
diff --git a/activerecord/lib/active_record/locking/optimistic.rb b/activerecord/lib/active_record/locking/optimistic.rb
index 9f053453bd..008cda46cd 100644
--- a/activerecord/lib/active_record/locking/optimistic.rb
+++ b/activerecord/lib/active_record/locking/optimistic.rb
@@ -66,6 +66,15 @@ module ActiveRecord
           send(lock_col + '=', previous_lock_value + 1)
         end
 
+        def _create_record(attribute_names = self.attribute_names, *) # :nodoc:
+          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
+            attribute_names |= [self.class.locking_column]
+          end
+          super
+        end
+
         def _update_record(attribute_names = self.attribute_names) #:nodoc:
           return super unless locking_enabled?
           return 0 if attribute_names.empty?
@@ -116,12 +125,8 @@ module ActiveRecord
           relation = super
 
           if locking_enabled?
-            column_name = self.class.locking_column
-            column      = self.class.columns_hash[column_name]
-            substitute  = self.class.connection.substitute_at(column)
-
-            relation = relation.where(self.class.arel_table[column_name].eq(substitute))
-            relation.bind_values << [column, self[column_name].to_i]
+            locking_column = self.class.locking_column
+            relation = relation.where(locking_column => _read_attribute(locking_column))
           end
 
           relation
@@ -139,7 +144,7 @@ module ActiveRecord
 
         # Set the column to use for optimistic locking. Defaults to +lock_version+.
         def locking_column=(value)
-          clear_caches_calculated_from_columns
+          reload_schema_from_cache
           @locking_column = value.to_s
         end
 
@@ -185,11 +190,6 @@ module ActiveRecord
         super.to_i
       end
 
-      def changed?(old_value, *)
-        # Ensure we save if the default was `nil`
-        super || old_value == 0
-      end
-
       def init_with(coder)
         __setobj__(coder['subtype'])
       end
diff --git a/activerecord/lib/active_record/log_subscriber.rb b/activerecord/lib/active_record/log_subscriber.rb
index eb64d197f0..6b26d7be78 100644
--- a/activerecord/lib/active_record/log_subscriber.rb
+++ b/activerecord/lib/active_record/log_subscriber.rb
@@ -20,18 +20,14 @@ module ActiveRecord
       @odd = false
     end
 
-    def render_bind(column, value)
-      if column
-        if column.binary?
-          # This specifically deals with the PG adapter that casts bytea columns into a Hash.
-          value = value[:value] if value.is_a?(Hash)
-          value = value ? "<#{value.bytesize} bytes of binary data>" : "<NULL binary data>"
-        end
-
-        [column.name, value]
+    def render_bind(attribute)
+      value = if attribute.type.binary? && attribute.value
+        "<#{attribute.value.bytesize} bytes of binary data>"
       else
-        [nil, value]
+        attribute.value_for_database
       end
+
+      [attribute.name, value]
     end
 
     def sql(event)
@@ -47,9 +43,7 @@ module ActiveRecord
       binds = nil
 
       unless (payload[:binds] || []).empty?
-        binds = "  " + payload[:binds].map { |col,v|
-          render_bind(col, v)
-        }.inspect
+        binds = "  " + payload[:binds].map { |attr| render_bind(attr) }.inspect
       end
 
       if odd?
diff --git a/activerecord/lib/active_record/model_schema.rb b/activerecord/lib/active_record/model_schema.rb
index 641512d323..293db1c57f 100644
--- a/activerecord/lib/active_record/model_schema.rb
+++ b/activerecord/lib/active_record/model_schema.rb
@@ -111,17 +111,6 @@ module ActiveRecord
       #   class Mouse < ActiveRecord::Base
       #     self.table_name = "mice"
       #   end
-      #
-      # Alternatively, you can override the table_name method to define your
-      # own computation. (Possibly using <tt>super</tt> to manipulate the default
-      # table name.) Example:
-      #
-      #   class Post < ActiveRecord::Base
-      #     def self.table_name
-      #       "special_" + super
-      #     end
-      #   end
-      #   Post.table_name # => "special_posts"
       def table_name
         reset_table_name unless defined?(@table_name)
         @table_name
@@ -132,9 +121,6 @@ module ActiveRecord
       #   class Project < ActiveRecord::Base
       #     self.table_name = "project"
       #   end
-      #
-      # You can also just define your own <tt>self.table_name</tt> method; see
-      # the documentation for ActiveRecord::Base#table_name.
       def table_name=(value)
         value = value && value.to_s
 
@@ -231,28 +217,37 @@ module ActiveRecord
       end
 
       def attributes_builder # :nodoc:
-        @attributes_builder ||= AttributeSet::Builder.new(column_types, primary_key)
+        @attributes_builder ||= AttributeSet::Builder.new(attribute_types, primary_key)
       end
 
-      def column_types # :nodoc:
-        @column_types ||= columns_hash.transform_values(&:cast_type).tap do |h|
-          h.default = Type::Value.new
-        end
+      def columns_hash # :nodoc:
+        load_schema
+        @columns_hash
+      end
+
+      def columns
+        load_schema
+        @columns ||= columns_hash.values
+      end
+
+      def attribute_types # :nodoc:
+        load_schema
+        @attribute_types ||= Hash.new(Type::Value.new)
       end
 
       def type_for_attribute(attr_name) # :nodoc:
-        column_types[attr_name]
+        attribute_types[attr_name]
       end
 
       # Returns a hash where the keys are column names and the values are
       # default values when instantiating the AR object for this table.
       def column_defaults
+        load_schema
         _default_attributes.to_hash
       end
 
       def _default_attributes # :nodoc:
-        @default_attributes ||= attributes_builder.build_from_database(
-          raw_default_values)
+        @default_attributes ||= AttributeSet.new({})
       end
 
       # Returns an array of column names as strings.
@@ -295,19 +290,53 @@ module ActiveRecord
       def reset_column_information
         connection.clear_cache!
         undefine_attribute_methods
-        connection.schema_cache.clear_table_cache!(table_name) if table_exists?
+        connection.schema_cache.clear_table_cache!(table_name)
 
-        @arel_engine        = nil
-        @arel_table         = nil
-        @column_names       = nil
-        @column_types       = nil
-        @content_columns    = nil
-        @default_attributes = nil
-        @inheritance_column = nil unless defined?(@explicit_inheritance_column) && @explicit_inheritance_column
+        reload_schema_from_cache
       end
 
       private
 
+      def schema_loaded?
+        defined?(@columns_hash) && @columns_hash
+      end
+
+      def load_schema
+        unless schema_loaded?
+          load_schema!
+        end
+      end
+
+      def load_schema!
+        @columns_hash = connection.schema_cache.columns_hash(table_name)
+        @columns_hash.each do |name, column|
+          define_attribute(
+            name,
+            column.cast_type,
+            default: column.default,
+            user_provided_default: false
+          )
+        end
+      end
+
+      def reload_schema_from_cache
+        @arel_engine = nil
+        @arel_table = nil
+        @column_names = nil
+        @attribute_types = nil
+        @content_columns = nil
+        @default_attributes = nil
+        @inheritance_column = nil unless defined?(@explicit_inheritance_column) && @explicit_inheritance_column
+        @attributes_builder = nil
+        @column_names = nil
+        @attribute_types = nil
+        @columns = nil
+        @columns_hash = nil
+        @content_columns = nil
+        @default_attributes = nil
+        @attribute_names = nil
+      end
+
       # Guesses the table name, but does not decorate it with prefix and suffix information.
       def undecorated_table_name(class_name = base_class.name)
         table_name = class_name.to_s.demodulize.underscore
@@ -331,10 +360,6 @@ module ActiveRecord
           base.table_name
         end
       end
-
-      def raw_default_values
-        columns_hash.transform_values(&:default)
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/nested_attributes.rb b/activerecord/lib/active_record/nested_attributes.rb
index 846e1162a9..117a128579 100644
--- a/activerecord/lib/active_record/nested_attributes.rb
+++ b/activerecord/lib/active_record/nested_attributes.rb
@@ -312,7 +312,7 @@ module ActiveRecord
         attr_names.each do |association_name|
           if reflection = _reflect_on_association(association_name)
             reflection.autosave = true
-            add_autosave_association_callbacks(reflection)
+            define_autosave_validation_callbacks(reflection)
 
             nested_attributes_options = self.nested_attributes_options.dup
             nested_attributes_options[association_name.to_sym] = options
diff --git a/activerecord/lib/active_record/null_relation.rb b/activerecord/lib/active_record/null_relation.rb
index b406da14dc..63ca29305d 100644
--- a/activerecord/lib/active_record/null_relation.rb
+++ b/activerecord/lib/active_record/null_relation.rb
@@ -75,5 +75,9 @@ module ActiveRecord
     def exists?(_id = false)
       false
     end
+
+    def or(other)
+      other.spawn
+    end
   end
 end
diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index f53c5f17ef..22112fe8ff 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -113,9 +113,9 @@ module ActiveRecord
     # the current time. However, if you supply <tt>touch: false</tt>, these
     # timestamps will not be updated.
     #
-    # There's a series of callbacks associated with +save+. If any of the
-    # <tt>before_*</tt> callbacks return +false+ the action is cancelled and
-    # +save+ returns +false+. See ActiveRecord::Callbacks for further
+    # There's a series of callbacks associated with #save. If any of the
+    # <tt>before_*</tt> callbacks throws +:abort+ the action is cancelled and
+    # #save returns +false+. See ActiveRecord::Callbacks for further
     # details.
     #
     # Attributes marked as readonly are silently ignored if the record is
@@ -139,9 +139,9 @@ module ActiveRecord
     # the current time. However, if you supply <tt>touch: false</tt>, these
     # timestamps will not be updated.
     #
-    # There's a series of callbacks associated with <tt>save!</tt>. If any of
-    # the <tt>before_*</tt> callbacks return +false+ the action is cancelled
-    # and <tt>save!</tt> raises ActiveRecord::RecordNotSaved. See
+    # There's a series of callbacks associated with #save!. If any of
+    # the <tt>before_*</tt> callbacks throws +:abort+ the action is cancelled
+    # and #save! raises ActiveRecord::RecordNotSaved. See
     # ActiveRecord::Callbacks for further details.
     #
     # Attributes marked as readonly are silently ignored if the record is
@@ -171,10 +171,10 @@ module ActiveRecord
     # Deletes the record in the database and freezes this instance to reflect
     # that no changes should be made (since they can't be persisted).
     #
-    # There's a series of callbacks associated with <tt>destroy</tt>. If
-    # the <tt>before_destroy</tt> callback return +false+ the action is cancelled
-    # and <tt>destroy</tt> returns +false+. See
-    # ActiveRecord::Callbacks for further details.
+    # There's a series of callbacks associated with #destroy. If the
+    # <tt>before_destroy</tt> callback throws +:abort+ the action is cancelled
+    # and #destroy returns +false+.
+    # See ActiveRecord::Callbacks for further details.
     def destroy
       raise ReadOnlyRecord, "#{self.class} is marked as readonly" if readonly?
       destroy_associations
@@ -186,10 +186,10 @@ module ActiveRecord
     # Deletes the record in the database and freezes this instance to reflect
     # that no changes should be made (since they can't be persisted).
     #
-    # There's a series of callbacks associated with <tt>destroy!</tt>. If
-    # the <tt>before_destroy</tt> callback return +false+ the action is cancelled
-    # and <tt>destroy!</tt> raises ActiveRecord::RecordNotDestroyed. See
-    # ActiveRecord::Callbacks for further details.
+    # There's a series of callbacks associated with #destroy!. If the
+    # <tt>before_destroy</tt> callback throws +:abort+ the action is cancelled
+    # and #destroy! raises ActiveRecord::RecordNotDestroyed.
+    # See ActiveRecord::Callbacks for further details.
     def destroy!
       destroy || raise(ActiveRecord::RecordNotDestroyed, self)
     end
@@ -245,8 +245,8 @@ module ActiveRecord
     def update_attribute(name, value)
       name = name.to_s
       verify_readonly_attribute(name)
-      send("#{name}=", value)
-      save(validate: false)
+      public_send("#{name}=", value)
+      save(validate: false) if changed?
     end
 
     # Updates the attributes of the model from the passed-in hash and saves the
@@ -352,7 +352,7 @@ module ActiveRecord
     # method toggles directly the underlying value without calling any setter.
     # Returns +self+.
     def toggle(attribute)
-      self[attribute] = !send("#{attribute}?")
+      self[attribute] = !public_send("#{attribute}?")
       self
     end
 
@@ -495,15 +495,7 @@ module ActiveRecord
     end
 
     def relation_for_destroy
-      pk         = self.class.primary_key
-      column     = self.class.columns_hash[pk]
-      substitute = self.class.connection.substitute_at(column)
-
-      relation = self.class.unscoped.where(
-        self.class.arel_table[pk].eq(substitute))
-
-      relation.bind_values = [[column, id]]
-      relation
+      self.class.unscoped.where(self.class.primary_key => id)
     end
 
     def create_or_update(*args)
diff --git a/activerecord/lib/active_record/querying.rb b/activerecord/lib/active_record/querying.rb
index e8de4db3a7..4e597590e9 100644
--- a/activerecord/lib/active_record/querying.rb
+++ b/activerecord/lib/active_record/querying.rb
@@ -7,7 +7,7 @@ module ActiveRecord
     delegate :find_by, :find_by!, to: :all
     delegate :destroy, :destroy_all, :delete, :delete_all, :update, :update_all, to: :all
     delegate :find_each, :find_in_batches, to: :all
-    delegate :select, :group, :order, :except, :reorder, :limit, :offset, :joins,
+    delegate :select, :group, :order, :except, :reorder, :limit, :offset, :joins, :or,
              :where, :rewhere, :preload, :eager_load, :includes, :from, :lock, :readonly,
              :having, :create_with, :uniq, :distinct, :references, :none, :unscope, to: :all
     delegate :count, :average, :minimum, :maximum, :sum, :calculate, to: :all
@@ -55,11 +55,12 @@ module ActiveRecord
     # The use of this method should be restricted to complicated SQL queries that can't be executed
     # using the ActiveRecord::Calculations class methods. Look into those before using this.
     #
-    # ==== Parameters
+    #   Product.count_by_sql "SELECT COUNT(*) FROM sales s, customers c WHERE s.customer_id = c.id"
+    #   # => 12
     #
-    # * +sql+ - An SQL statement which should return a count query from the database, see the example below.
+    # ==== Parameters
     #
-    #   Product.count_by_sql "SELECT COUNT(*) FROM sales s, customers c WHERE s.customer_id = c.id"
+    # * +sql+ - An SQL statement which should return a count query from the database, see the example above.
     def count_by_sql(sql)
       sql = sanitize_conditions(sql)
       connection.select_value(sql, "#{name} Count").to_i
diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index 7696ef13c7..dab5a502a5 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -153,15 +153,6 @@ module ActiveRecord
         JoinKeys.new(foreign_key, active_record_primary_key)
       end
 
-      def source_macro
-        ActiveSupport::Deprecation.warn(<<-MSG.squish)
-          ActiveRecord::Base.source_macro is deprecated and will be removed
-          without replacement.
-        MSG
-
-        macro
-      end
-
       def constraints
         scope_chain.flatten
       end
@@ -352,13 +343,10 @@ module ActiveRecord
         return unless scope
 
         if scope.arity > 0
-          ActiveSupport::Deprecation.warn(<<-MSG.squish)
+          raise ArgumentError, <<-MSG.squish
             The association scope '#{name}' is instance dependent (the scope
-            block takes an argument). Preloading happens before the individual
-            instances are created. This means that there is no instance being
-            passed to the association scope. This will most likely result in
-            broken or incorrect behavior. Joining, Preloading and eager loading
-            of these associations is deprecated and will be removed in the future.
+            block takes an argument). Preloading instance dependent scopes is
+            not supported.
           MSG
         end
       end
@@ -763,16 +751,6 @@ module ActiveRecord
         source_reflection.join_keys(association_klass)
       end
 
-      # The macro used by the source association
-      def source_macro
-        ActiveSupport::Deprecation.warn(<<-MSG.squish)
-          ActiveRecord::Base.source_macro is deprecated and will be removed
-          without replacement.
-        MSG
-
-        source_reflection.source_macro
-      end
-
       # A through association is nested if there would be more than one join table
       def nested?
         chain.length > 2
diff --git a/activerecord/lib/active_record/relation.rb b/activerecord/lib/active_record/relation.rb
index ab3debc03b..8073eb99dd 100644
--- a/activerecord/lib/active_record/relation.rb
+++ b/activerecord/lib/active_record/relation.rb
@@ -1,18 +1,19 @@
 # -*- coding: utf-8 -*-
-require 'arel/collectors/bind'
+require "arel/collectors/bind"
 
 module ActiveRecord
   # = Active Record Relation
   class Relation
     MULTI_VALUE_METHODS  = [:includes, :eager_load, :preload, :select, :group,
-                            :order, :joins, :where, :having, :bind, :references,
+                            :order, :joins, :references,
                             :extending, :unscope]
 
-    SINGLE_VALUE_METHODS = [:limit, :offset, :lock, :readonly, :from, :reordering,
+    SINGLE_VALUE_METHODS = [:limit, :offset, :lock, :readonly, :reordering,
                             :reverse_order, :distinct, :create_with, :uniq]
+    CLAUSE_METHODS = [:where, :having, :from]
     INVALID_METHODS_FOR_DELETE_ALL = [:limit, :distinct, :offset, :group, :having]
 
-    VALUE_METHODS = MULTI_VALUE_METHODS + SINGLE_VALUE_METHODS
+    VALUE_METHODS = MULTI_VALUE_METHODS + SINGLE_VALUE_METHODS + CLAUSE_METHODS
 
     include FinderMethods, Calculations, SpawnMethods, QueryMethods, Batches, Explain, Delegation
 
@@ -33,7 +34,6 @@ module ActiveRecord
       # This method is a hot spot, so for now, use Hash[] to dup the hash.
       #   https://bugs.ruby-lang.org/issues/7166
       @values        = Hash[@values]
-      @values[:bind] = @values[:bind].dup if @values.key? :bind
       reset
     end
 
@@ -81,7 +81,7 @@ module ActiveRecord
       end
 
       relation = scope.where(@klass.primary_key => (id_was || id))
-      bvs = binds + relation.bind_values
+      bvs = binds + relation.bound_attributes
       um = relation
         .arel
         .compile_update(substitutes, @klass.primary_key)
@@ -95,11 +95,11 @@ module ActiveRecord
 
     def substitute_values(values) # :nodoc:
       binds = values.map do |arel_attr, value|
-        [@klass.columns_hash[arel_attr.name], value]
+        QueryAttribute.new(arel_attr.name, value, klass.type_for_attribute(arel_attr.name))
       end
 
-      substitutes = values.each_with_index.map do |(arel_attr, _), i|
-        [arel_attr, @klass.connection.substitute_at(binds[i][0])]
+      substitutes = values.map do |(arel_attr, _)|
+        [arel_attr, connection.substitute_at(klass.columns_hash[arel_attr.name])]
       end
 
       [substitutes, binds]
@@ -342,8 +342,7 @@ module ActiveRecord
         stmt.wheres = arel.constraints
       end
 
-      bvs = arel.bind_values + bind_values
-      @klass.connection.update stmt, 'SQL', bvs
+      @klass.connection.update stmt, 'SQL', bound_attributes
     end
 
     # Updates an object (or multiple objects) and saves it to the database, if validations pass.
@@ -467,8 +466,10 @@ module ActiveRecord
       invalid_methods = INVALID_METHODS_FOR_DELETE_ALL.select { |method|
         if MULTI_VALUE_METHODS.include?(method)
           send("#{method}_values").any?
-        else
+        elsif SINGLE_VALUE_METHODS.include?(method)
           send("#{method}_value")
+        elsif CLAUSE_METHODS.include?(method)
+          send("#{method}_clause").any?
         end
       }
       if invalid_methods.any?
@@ -487,7 +488,7 @@ module ActiveRecord
           stmt.wheres = arel.constraints
         end
 
-        affected = @klass.connection.delete(stmt, 'SQL', bind_values)
+        affected = @klass.connection.delete(stmt, 'SQL', bound_attributes)
 
         reset
         affected
@@ -557,10 +558,10 @@ module ActiveRecord
                       find_with_associations { |rel| relation = rel }
                     end
 
-                    arel  = relation.arel
-                    binds = (arel.bind_values + relation.bind_values).dup
-                    binds.map! { |bv| connection.quote(*bv.reverse) }
-                    collect = visitor.accept(arel.ast, Arel::Collectors::Bind.new)
+                    binds = relation.bound_attributes
+                    binds = connection.prepare_binds_for_database(binds)
+                    binds.map! { |value| connection.quote(value) }
+                    collect = visitor.accept(relation.arel.ast, Arel::Collectors::Bind.new)
                     collect.substitute_binds(binds).join
                   end
     end
@@ -570,22 +571,7 @@ module ActiveRecord
     #   User.where(name: 'Oscar').where_values_hash
     #   # => {name: "Oscar"}
     def where_values_hash(relation_table_name = table_name)
-      equalities = where_values.grep(Arel::Nodes::Equality).find_all { |node|
-        node.left.relation.name == relation_table_name
-      }
-
-      binds = Hash[bind_values.find_all(&:first).map { |column, v| [column.name, v] }]
-
-      Hash[equalities.map { |where|
-        name = where.left.name
-        [name, binds.fetch(name.to_s) {
-          case where.right
-          when Array then where.right.map(&:val)
-          when Arel::Nodes::Casted, Arel::Nodes::Quoted
-            where.right.val
-          end
-        }]
-      }]
+      where_clause.to_h(relation_table_name)
     end
 
     def scope_for_create
@@ -648,7 +634,7 @@ module ActiveRecord
     private
 
     def exec_queries
-      @records = eager_loading? ? find_with_associations : @klass.find_by_sql(arel, arel.bind_values + bind_values)
+      @records = eager_loading? ? find_with_associations : @klass.find_by_sql(arel, bound_attributes)
 
       preload = preload_values
       preload +=  includes_values unless eager_loading?
diff --git a/activerecord/lib/active_record/relation/calculations.rb b/activerecord/lib/active_record/relation/calculations.rb
index 1d4cb1a83b..63e0d2fc21 100644
--- a/activerecord/lib/active_record/relation/calculations.rb
+++ b/activerecord/lib/active_record/relation/calculations.rb
@@ -166,8 +166,8 @@ module ActiveRecord
         relation.select_values = column_names.map { |cn|
           columns_hash.key?(cn) ? arel_table[cn] : cn
         }
-        result = klass.connection.select_all(relation.arel, nil, relation.arel.bind_values + bind_values)
-        result.cast_values(klass.column_types)
+        result = klass.connection.select_all(relation.arel, nil, bound_attributes)
+        result.cast_values(klass.attribute_types)
       end
     end
 
@@ -227,14 +227,11 @@ module ActiveRecord
 
       column_alias = column_name
 
-      bind_values = nil
-
       if operation == "count" && (relation.limit_value || relation.offset_value)
         # Shortcut when limit is zero.
         return 0 if relation.limit_value == 0
 
         query_builder = build_count_subquery(relation, column_name, distinct)
-        bind_values = query_builder.bind_values + relation.bind_values
       else
         column = aggregate_column(column_name)
 
@@ -245,10 +242,9 @@ module ActiveRecord
         relation.select_values = [select_value]
 
         query_builder = relation.arel
-        bind_values = query_builder.bind_values + relation.bind_values
       end
 
-      result = @klass.connection.select_all(query_builder, nil, bind_values)
+      result = @klass.connection.select_all(query_builder, nil, bound_attributes)
       row    = result.first
       value  = row && row.values.first
       column = result.column_types.fetch(column_alias) do
@@ -290,7 +286,7 @@ module ActiveRecord
           operation,
           distinct).as(aggregate_alias)
       ]
-      select_values += select_values unless having_values.empty?
+      select_values += select_values unless having_clause.empty?
 
       select_values.concat group_fields.zip(group_aliases).map { |field,aliaz|
         if field.respond_to?(:as)
@@ -304,11 +300,11 @@ module ActiveRecord
       relation.group_values  = group
       relation.select_values = select_values
 
-      calculated_data = @klass.connection.select_all(relation, nil, relation.arel.bind_values + bind_values)
+      calculated_data = @klass.connection.select_all(relation, nil, relation.bound_attributes)
 
       if association
         key_ids     = calculated_data.collect { |row| row[group_aliases.first] }
-        key_records = association.klass.base_class.find(key_ids)
+        key_records = association.klass.base_class.where(association.klass.base_class.primary_key => key_ids)
         key_records = Hash[key_records.map { |r| [r.id, r] }]
       end
 
@@ -378,11 +374,9 @@ module ActiveRecord
 
       aliased_column = aggregate_column(column_name == :all ? 1 : column_name).as(column_alias)
       relation.select_values = [aliased_column]
-      arel = relation.arel
-      subquery = arel.as(subquery_alias)
+      subquery = relation.arel.as(subquery_alias)
 
       sm = Arel::SelectManager.new relation.engine
-      sm.bind_values = arel.bind_values
       select_value = operation_over_aggregate_column(column_alias, 'count', distinct)
       sm.project(select_value).from(subquery)
     end
diff --git a/activerecord/lib/active_record/relation/delegation.rb b/activerecord/lib/active_record/relation/delegation.rb
index 50f4d5c7ab..d4a8823cfe 100644
--- a/activerecord/lib/active_record/relation/delegation.rb
+++ b/activerecord/lib/active_record/relation/delegation.rb
@@ -1,6 +1,5 @@
 require 'set'
 require 'active_support/concern'
-require 'active_support/deprecation'
 
 module ActiveRecord
   module Delegation # :nodoc:
diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index 088bc203b7..fb47d915ff 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -307,11 +307,11 @@ module ActiveRecord
         relation = relation.where(conditions)
       else
         unless conditions == :none
-          relation = where(primary_key => conditions)
+          relation = relation.where(primary_key => conditions)
         end
       end
 
-      connection.select_value(relation, "#{name} Exists", relation.arel.bind_values + relation.bind_values) ? true : false
+      connection.select_value(relation, "#{name} Exists", relation.bound_attributes) ? true : false
     end
 
     # This method is called whenever no records are found with either a single
@@ -365,7 +365,7 @@ module ActiveRecord
           []
         else
           arel = relation.arel
-          rows = connection.select_all(arel, 'SQL', arel.bind_values + relation.bind_values)
+          rows = connection.select_all(arel, 'SQL', relation.bound_attributes)
           join_dependency.instantiate(rows, aliases)
         end
       end
@@ -410,7 +410,7 @@ module ActiveRecord
       relation = relation.except(:select).select(values).distinct!
       arel = relation.arel
 
-      id_rows = @klass.connection.select_all(arel, 'SQL', arel.bind_values + relation.bind_values)
+      id_rows = @klass.connection.select_all(arel, 'SQL', relation.bound_attributes)
       id_rows.map {|row| row[primary_key]}
     end
 
diff --git a/activerecord/lib/active_record/relation/from_clause.rb b/activerecord/lib/active_record/relation/from_clause.rb
new file mode 100644
index 0000000000..a93952fa30
--- /dev/null
+++ b/activerecord/lib/active_record/relation/from_clause.rb
@@ -0,0 +1,32 @@
+module ActiveRecord
+  class Relation
+    class FromClause
+      attr_reader :value, :name
+
+      def initialize(value, name)
+        @value = value
+        @name = name
+      end
+
+      def binds
+        if value.is_a?(Relation)
+          value.bound_attributes
+        else
+          []
+        end
+      end
+
+      def merge(other)
+        self
+      end
+
+      def empty?
+        value.nil?
+      end
+
+      def self.empty
+        new(nil, nil)
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/relation/merger.rb b/activerecord/lib/active_record/relation/merger.rb
index afb0b208c3..65b607ff1c 100644
--- a/activerecord/lib/active_record/relation/merger.rb
+++ b/activerecord/lib/active_record/relation/merger.rb
@@ -49,9 +49,9 @@ module ActiveRecord
         @other    = other
       end
 
-      NORMAL_VALUES = Relation::SINGLE_VALUE_METHODS +
-                      Relation::MULTI_VALUE_METHODS -
-                      [:joins, :where, :order, :bind, :reverse_order, :lock, :create_with, :reordering, :from] # :nodoc:
+      NORMAL_VALUES = Relation::VALUE_METHODS -
+                      Relation::CLAUSE_METHODS -
+                      [:joins, :order, :reverse_order, :lock, :create_with, :reordering] # :nodoc:
 
       def normal_values
         NORMAL_VALUES
@@ -75,6 +75,7 @@ module ActiveRecord
 
         merge_multi_values
         merge_single_values
+        merge_clauses
         merge_joins
 
         relation
@@ -107,20 +108,6 @@ module ActiveRecord
       end
 
       def merge_multi_values
-        lhs_wheres = relation.where_values
-        rhs_wheres = other.where_values
-
-        lhs_binds  = relation.bind_values
-        rhs_binds  = other.bind_values
-
-        removed, kept = partition_overwrites(lhs_wheres, rhs_wheres)
-
-        where_values = kept + rhs_wheres
-        bind_values  = filter_binds(lhs_binds, removed) + rhs_binds
-
-        relation.where_values = where_values
-        relation.bind_values  = bind_values
-
         if other.reordering_value
           # override any order specified in the original relation
           relation.reorder! other.order_values
@@ -133,36 +120,18 @@ module ActiveRecord
       end
 
       def merge_single_values
-        relation.from_value          = other.from_value unless relation.from_value
-        relation.lock_value          = other.lock_value unless relation.lock_value
+        relation.lock_value ||= other.lock_value
 
         unless other.create_with_value.blank?
           relation.create_with_value = (relation.create_with_value || {}).merge(other.create_with_value)
         end
       end
 
-      def filter_binds(lhs_binds, removed_wheres)
-        return lhs_binds if removed_wheres.empty?
-
-        set = Set.new removed_wheres.map { |x| x.left.name.to_s }
-        lhs_binds.dup.delete_if { |col,_| set.include? col.name }
-      end
-
-      # Remove equalities from the existing relation with a LHS which is
-      # present in the relation being merged in.
-      # returns [things_to_remove, things_to_keep]
-      def partition_overwrites(lhs_wheres, rhs_wheres)
-        if lhs_wheres.empty? || rhs_wheres.empty?
-          return [[], lhs_wheres]
-        end
-
-        nodes = rhs_wheres.find_all do |w|
-          w.respond_to?(:operator) && w.operator == :==
-        end
-        seen = Set.new(nodes) { |node| node.left }
-
-        lhs_wheres.partition do |w|
-          w.respond_to?(:operator) && w.operator == :== && seen.include?(w.left)
+      def merge_clauses
+        CLAUSE_METHODS.each do |name|
+          clause = relation.send("#{name}_clause")
+          other_clause = other.send("#{name}_clause")
+          relation.send("#{name}_clause=", clause.merge(other_clause))
         end
       end
     end
diff --git a/activerecord/lib/active_record/relation/predicate_builder.rb b/activerecord/lib/active_record/relation/predicate_builder.rb
index 567efce8ae..43e9afe853 100644
--- a/activerecord/lib/active_record/relation/predicate_builder.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder.rb
@@ -28,6 +28,11 @@ module ActiveRecord
       expand_from_hash(attributes)
     end
 
+    def create_binds(attributes)
+      attributes = convert_dot_notation_to_hash(attributes.stringify_keys)
+      create_binds_for_hash(attributes)
+    end
+
     def expand(column, value)
       # Find the foreign key when using queries such as:
       # Post.where(author: author)
@@ -80,16 +85,43 @@ module ActiveRecord
 
       attributes.flat_map do |key, value|
         if value.is_a?(Hash)
-          builder = self.class.new(table.associated_table(key))
-          builder.expand_from_hash(value)
+          associated_predicate_builder(key).expand_from_hash(value)
         else
           expand(key, value)
         end
       end
     end
 
+
+    def create_binds_for_hash(attributes)
+      result = attributes.dup
+      binds = []
+
+      attributes.each do |column_name, value|
+        case value
+        when Hash
+          attrs, bvs = associated_predicate_builder(column_name).create_binds_for_hash(value)
+          result[column_name] = attrs
+          binds += bvs
+        when Relation
+          binds += value.bound_attributes
+        else
+          if can_be_bound?(column_name, value)
+            result[column_name] = Arel::Nodes::BindParam.new
+            binds << Relation::QueryAttribute.new(column_name.to_s, value, table.type(column_name))
+          end
+        end
+      end
+
+      [result, binds]
+    end
+
     private
 
+    def associated_predicate_builder(association_name)
+      self.class.new(table.associated_table(association_name))
+    end
+
     def convert_dot_notation_to_hash(attributes)
       dot_notation = attributes.keys.select { |s| s.include?(".") }
 
@@ -107,5 +139,11 @@ module ActiveRecord
     def handler_for(object)
       @handlers.detect { |klass, _| klass === object }.last
     end
+
+    def can_be_bound?(column_name, value)
+      !value.nil? &&
+        handler_for(value).is_a?(BasicObjectHandler) &&
+        !table.associated_with?(column_name)
+    end
   end
 end
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 4b5f5773a0..95dbd6a77f 100644
--- a/activerecord/lib/active_record/relation/predicate_builder/array_handler.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder/array_handler.rb
@@ -1,5 +1,3 @@
-require 'active_support/core_ext/string/filters'
-
 module ActiveRecord
   class PredicateBuilder
     class ArrayHandler # :nodoc:
diff --git a/activerecord/lib/active_record/relation/query_attribute.rb b/activerecord/lib/active_record/relation/query_attribute.rb
new file mode 100644
index 0000000000..e69319b4de
--- /dev/null
+++ b/activerecord/lib/active_record/relation/query_attribute.rb
@@ -0,0 +1,19 @@
+require 'active_record/attribute'
+
+module ActiveRecord
+  class Relation
+    class QueryAttribute < Attribute
+      def type_cast(value)
+        value
+      end
+
+      def value_for_database
+        @value_for_database ||= super
+      end
+
+      def with_cast_value(value)
+        QueryAttribute.new(name, value, type)
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index ef380abfe8..7514401072 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -1,6 +1,9 @@
-require 'active_support/core_ext/array/wrap'
-require 'active_support/core_ext/string/filters'
+require "active_record/relation/from_clause"
+require "active_record/relation/query_attribute"
+require "active_record/relation/where_clause"
+require "active_record/relation/where_clause_factory"
 require 'active_model/forbidden_attributes_protection'
+require 'active_support/core_ext/string/filters'
 
 module ActiveRecord
   module QueryMethods
@@ -39,38 +42,24 @@ module ActiveRecord
       #    User.where.not(name: "Jon", role: "admin")
       #    # SELECT * FROM users WHERE name != 'Jon' AND role != 'admin'
       def not(opts, *rest)
-        where_value = @scope.send(:build_where, opts, rest).map do |rel|
-          case rel
-          when NilClass
-            raise ArgumentError, 'Invalid argument for .where.not(), got nil.'
-          when Arel::Nodes::In
-            Arel::Nodes::NotIn.new(rel.left, rel.right)
-          when Arel::Nodes::Equality
-            Arel::Nodes::NotEqual.new(rel.left, rel.right)
-          when String
-            Arel::Nodes::Not.new(Arel::Nodes::SqlLiteral.new(rel))
-          else
-            Arel::Nodes::Not.new(rel)
-          end
-        end
+        where_clause = @scope.send(:where_clause_factory).build(opts, rest)
 
         @scope.references!(PredicateBuilder.references(opts)) if Hash === opts
-        @scope.where_values += where_value
+        @scope.where_clause += where_clause.invert
         @scope
       end
     end
 
     Relation::MULTI_VALUE_METHODS.each do |name|
       class_eval <<-CODE, __FILE__, __LINE__ + 1
-        def #{name}_values                   # def select_values
-          @values[:#{name}] || []            #   @values[:select] || []
-        end                                  # end
-                                             #
-        def #{name}_values=(values)          # def select_values=(values)
-          raise ImmutableRelation if @loaded #   raise ImmutableRelation if @loaded
-          check_cached_relation
-          @values[:#{name}] = values         #   @values[:select] = values
-        end                                  # end
+        def #{name}_values                    # def select_values
+          @values[:#{name}] || []             #   @values[:select] || []
+        end                                   # end
+                                              #
+        def #{name}_values=(values)           # def select_values=(values)
+          assert_mutability!                  #   assert_mutability!
+          @values[:#{name}] = values          #   @values[:select] = values
+        end                                   # end
       CODE
     end
 
@@ -85,21 +74,27 @@ module ActiveRecord
     Relation::SINGLE_VALUE_METHODS.each do |name|
       class_eval <<-CODE, __FILE__, __LINE__ + 1
         def #{name}_value=(value)            # def readonly_value=(value)
-          raise ImmutableRelation if @loaded #   raise ImmutableRelation if @loaded
-          check_cached_relation
+          assert_mutability!                 #   assert_mutability!
           @values[:#{name}] = value          #   @values[:readonly] = value
         end                                  # end
       CODE
     end
 
-    def check_cached_relation # :nodoc:
-      if defined?(@arel) && @arel
-        @arel = nil
-        ActiveSupport::Deprecation.warn(<<-MSG.squish)
-          Modifying already cached Relation. The cache will be reset. Use a
-          cloned Relation to prevent this warning.
-        MSG
-      end
+    Relation::CLAUSE_METHODS.each do |name|
+      class_eval <<-CODE, __FILE__, __LINE__ + 1
+        def #{name}_clause                           # def where_clause
+          @values[:#{name}] || new_#{name}_clause    #   @values[:where] || new_where_clause
+        end                                          # end
+                                                     #
+        def #{name}_clause=(value)                   # def where_clause=(value)
+          assert_mutability!                         #   assert_mutability!
+          @values[:#{name}] = value                  #   @values[:where] = value
+        end                                          # end
+      CODE
+    end
+
+    def bound_attributes
+      from_clause.binds + arel.bind_values + where_clause.binds + having_clause.binds
     end
 
     def create_with_value # :nodoc:
@@ -404,9 +399,8 @@ module ActiveRecord
               raise ArgumentError, "Hash arguments in .unscope(*args) must have :where as the key."
             end
 
-            Array(target_value).each do |val|
-              where_unscoping(val)
-            end
+            target_values = Array(target_value).map(&:to_s)
+            self.where_clause = where_clause.except(*target_values)
           end
         else
           raise ArgumentError, "Unrecognized scoping: #{args.inspect}. Use .unscope(where: :attribute_name) or .unscope(:order), for example."
@@ -437,15 +431,6 @@ module ActiveRecord
       self
     end
 
-    def bind(value) # :nodoc:
-      spawn.bind!(value)
-    end
-
-    def bind!(value) # :nodoc:
-      self.bind_values += [value]
-      self
-    end
-
     # Returns a new relation, which is the result of filtering the current relation
     # according to the conditions in the arguments.
     #
@@ -581,7 +566,7 @@ module ActiveRecord
         references!(PredicateBuilder.references(opts))
       end
 
-      self.where_values += build_where(opts, rest)
+      self.where_clause += where_clause_factory.build(opts, rest)
       self
     end
 
@@ -597,6 +582,37 @@ module ActiveRecord
       unscope(where: conditions.keys).where(conditions)
     end
 
+    # Returns a new relation, which is the logical union of this relation and the one passed as an
+    # argument.
+    #
+    # The two relations must be structurally compatible: they must be scoping the same model, and
+    # they must differ only by +where+ (if no +group+ has been defined) or +having+ (if a +group+ is
+    # present). Neither relation may have a +limit+, +offset+, or +uniq+ set.
+    #
+    #    Post.where("id = 1").or(Post.where("id = 2"))
+    #    # SELECT `posts`.* FROM `posts`  WHERE (('id = 1' OR 'id = 2'))
+    #
+    def or(other)
+      spawn.or!(other)
+    end
+
+    def or!(other) # :nodoc:
+      unless structurally_compatible_for_or?(other)
+        raise ArgumentError, 'Relation passed to #or must be structurally compatible'
+      end
+
+      self.where_clause = self.where_clause.or(other.where_clause)
+      self.having_clause = self.having_clause.or(other.having_clause)
+
+      self
+    end
+
+    private def structurally_compatible_for_or?(other) # :nodoc:
+      Relation::SINGLE_VALUE_METHODS.all? { |m| send("#{m}_value") == other.send("#{m}_value") } &&
+        (Relation::MULTI_VALUE_METHODS - [:extending]).all? { |m| send("#{m}_values") == other.send("#{m}_values") } &&
+        (Relation::CLAUSE_METHODS - [:having, :where]).all? { |m| send("#{m}_clause") != other.send("#{m}_clause") }
+    end
+
     # Allows to specify a HAVING clause. Note that you can't use HAVING
     # without also specifying a GROUP clause.
     #
@@ -608,7 +624,7 @@ module ActiveRecord
     def having!(opts, *rest) # :nodoc:
       references!(PredicateBuilder.references(opts)) if Hash === opts
 
-      self.having_values += build_where(opts, rest)
+      self.having_clause += having_clause_factory.build(opts, rest)
       self
     end
 
@@ -756,7 +772,7 @@ module ActiveRecord
     end
 
     def from!(value, subquery_name = nil) # :nodoc:
-      self.from_value = [value, subquery_name]
+      self.from_clause = Relation::FromClause.new(value, subquery_name)
       self
     end
 
@@ -857,26 +873,28 @@ module ActiveRecord
 
     private
 
+    def assert_mutability!
+      raise ImmutableRelation if @loaded
+      raise ImmutableRelation if defined?(@arel) && @arel
+    end
+
     def build_arel
       arel = Arel::SelectManager.new(table)
 
       build_joins(arel, joins_values.flatten) unless joins_values.empty?
 
-      collapse_wheres(arel, (where_values - [''])) #TODO: Add uniq with real value comparison / ignore uniqs that have binds
-
-      arel.having(*having_values.uniq.reject(&:blank?)) unless having_values.empty?
-
+      arel.where(where_clause.ast) unless where_clause.empty?
+      arel.having(having_clause.ast) unless having_clause.empty?
       arel.take(connection.sanitize_limit(limit_value)) if limit_value
       arel.skip(offset_value.to_i) if offset_value
-
-      arel.group(*group_values.uniq.reject(&:blank?)) unless group_values.empty?
+      arel.group(*arel_columns(group_values.uniq.reject(&:blank?))) unless group_values.empty?
 
       build_order(arel)
 
-      build_select(arel, select_values.uniq)
+      build_select(arel)
 
       arel.distinct(distinct_value)
-      arel.from(build_from) if from_value
+      arel.from(build_from) unless from_clause.empty?
       arel.lock(lock_value) if lock_value
 
       arel
@@ -887,114 +905,24 @@ module ActiveRecord
         raise ArgumentError, "Called unscope() with invalid unscoping argument ':#{scope}'. Valid arguments are :#{VALID_UNSCOPING_VALUES.to_a.join(", :")}."
       end
 
-      single_val_method = Relation::SINGLE_VALUE_METHODS.include?(scope)
-      unscope_code = "#{scope}_value#{'s' unless single_val_method}="
+      clause_method = Relation::CLAUSE_METHODS.include?(scope)
+      multi_val_method = Relation::MULTI_VALUE_METHODS.include?(scope)
+      if clause_method
+        unscope_code = "#{scope}_clause="
+      else
+        unscope_code = "#{scope}_value#{'s' if multi_val_method}="
+      end
 
       case scope
       when :order
         result = []
-      when :where
-        self.bind_values = []
       else
-        result = [] unless single_val_method
+        result = [] if multi_val_method
       end
 
       self.send(unscope_code, result)
     end
 
-    def where_unscoping(target_value)
-      target_value = target_value.to_s
-
-      where_values.reject! do |rel|
-        case rel
-        when Arel::Nodes::Between, Arel::Nodes::In, Arel::Nodes::NotIn, Arel::Nodes::Equality, Arel::Nodes::NotEqual, Arel::Nodes::LessThanOrEqual, Arel::Nodes::GreaterThanOrEqual
-          subrelation = (rel.left.kind_of?(Arel::Attributes::Attribute) ? rel.left : rel.right)
-          subrelation.name.to_s == target_value
-        end
-      end
-
-      bind_values.reject! { |col,_| col.name == target_value }
-    end
-
-    def custom_join_ast(table, joins)
-      joins = joins.reject(&:blank?)
-
-      return [] if joins.empty?
-
-      joins.map! do |join|
-        case join
-        when Array
-          join = Arel.sql(join.join(' ')) if array_of_strings?(join)
-        when String
-          join = Arel.sql(join)
-        end
-        table.create_string_join(join)
-      end
-    end
-
-    def collapse_wheres(arel, wheres)
-      predicates = wheres.map do |where|
-        next where if ::Arel::Nodes::Equality === where
-        where = Arel.sql(where) if String === where
-        Arel::Nodes::Grouping.new(where)
-      end
-
-      arel.where(Arel::Nodes::And.new(predicates)) if predicates.present?
-    end
-
-    def build_where(opts, other = [])
-      case opts
-      when String, Array
-        [@klass.send(:sanitize_sql, other.empty? ? opts : ([opts] + other))]
-      when Hash
-        opts = predicate_builder.resolve_column_aliases(opts)
-
-        tmp_opts, bind_values = create_binds(opts)
-        self.bind_values += bind_values
-
-        attributes = @klass.send(:expand_hash_conditions_for_aggregates, tmp_opts)
-        add_relations_to_bind_values(attributes)
-
-        predicate_builder.build_from_hash(attributes)
-      else
-        [opts]
-      end
-    end
-
-    def create_binds(opts)
-      bindable, non_binds = opts.partition do |column, value|
-        case value
-        when String, Integer, ActiveRecord::StatementCache::Substitute
-          @klass.columns_hash.include? column.to_s
-        else
-          false
-        end
-      end
-
-      association_binds, non_binds = non_binds.partition do |column, value|
-        value.is_a?(Hash) && association_for_table(column)
-      end
-
-      new_opts = {}
-      binds = []
-
-      bindable.each do |(column,value)|
-        binds.push [@klass.columns_hash[column.to_s], value]
-        new_opts[column] = connection.substitute_at(column)
-      end
-
-      association_binds.each do |(column, value)|
-        association_relation = association_for_table(column).klass.send(:relation)
-        association_new_opts, association_bind = association_relation.send(:create_binds, value)
-        new_opts[column] = association_new_opts
-        binds += association_bind
-      end
-
-      non_binds.each { |column,value| new_opts[column] = value }
-
-      [new_opts, binds]
-    end
-
     def association_for_table(table_name)
       table_name = table_name.to_s
       @klass._reflect_on_association(table_name) ||
@@ -1002,11 +930,11 @@ module ActiveRecord
     end
 
     def build_from
-      opts, name = from_value
+      opts = from_clause.value
+      name = from_clause.name
       case opts
       when Relation
         name ||= 'subquery'
-        self.bind_values = opts.bind_values + self.bind_values
         opts.arel.as(name.to_s)
       else
         opts
@@ -1028,13 +956,14 @@ module ActiveRecord
           raise 'unknown class: %s' % join.class.name
         end
       end
+      buckets.default = []
 
-      association_joins         = buckets[:association_join] || []
-      stashed_association_joins = buckets[:stashed_join] || []
-      join_nodes                = (buckets[:join_node] || []).uniq
-      string_joins              = (buckets[:string_join] || []).map(&:strip).uniq
+      association_joins         = buckets[:association_join]
+      stashed_association_joins = buckets[:stashed_join]
+      join_nodes                = buckets[:join_node].uniq
+      string_joins              = buckets[:string_join].map(&:strip).uniq
 
-      join_list = join_nodes + custom_join_ast(manager, string_joins)
+      join_list = join_nodes + convert_join_strings_to_ast(manager, string_joins)
 
       join_dependency = ActiveRecord::Associations::JoinDependency.new(
         @klass,
@@ -1054,22 +983,31 @@ module ActiveRecord
       manager
     end
 
-    def build_select(arel, selects)
-      if !selects.empty?
-        expanded_select = selects.map do |field|
-          if (Symbol === field || String === field) && columns_hash.key?(field.to_s)
-            arel_table[field]
-          else
-            field
-          end
-        end
+    def convert_join_strings_to_ast(table, joins)
+      joins
+        .flatten
+        .reject(&:blank?)
+        .map { |join| table.create_string_join(Arel.sql(join)) }
+    end
 
-        arel.project(*expanded_select)
+    def build_select(arel)
+      if select_values.any?
+        arel.project(*arel_columns(select_values.uniq))
       else
         arel.project(@klass.arel_table[Arel.star])
       end
     end
 
+    def arel_columns(columns)
+      columns.map do |field|
+        if (Symbol === field || String === field) && columns_hash.key?(field.to_s)
+          arel_table[field]
+        else
+          field
+        end
+      end
+    end
+
     def reverse_sql_order(order_query)
       order_query = ["#{quoted_table_name}.#{quoted_primary_key} ASC"] if order_query.empty?
 
@@ -1088,10 +1026,6 @@ module ActiveRecord
       end
     end
 
-    def array_of_strings?(o)
-      o.is_a?(Array) && o.all? { |obj| obj.is_a?(String) }
-    end
-
     def build_order(arel)
       orders = order_values.uniq
       orders.reject!(&:blank?)
@@ -1159,18 +1093,18 @@ module ActiveRecord
       end
     end
 
-    # This function is recursive just for better readablity.
-    # #where argument doesn't support more than one level nested hash in real world.
-    def add_relations_to_bind_values(attributes)
-      if attributes.is_a?(Hash)
-        attributes.each_value do |value|
-          if value.is_a?(ActiveRecord::Relation)
-            self.bind_values += value.bind_values
-          else
-            add_relations_to_bind_values(value)
-          end
-        end
-      end
+    def new_where_clause
+      Relation::WhereClause.empty
+    end
+    alias new_having_clause new_where_clause
+
+    def where_clause_factory
+      @where_clause_factory ||= Relation::WhereClauseFactory.new(klass, predicate_builder)
+    end
+    alias having_clause_factory where_clause_factory
+
+    def new_from_clause
+      Relation::FromClause.empty
     end
   end
 end
diff --git a/activerecord/lib/active_record/relation/spawn_methods.rb b/activerecord/lib/active_record/relation/spawn_methods.rb
index 01bddea6c9..dd3610d7aa 100644
--- a/activerecord/lib/active_record/relation/spawn_methods.rb
+++ b/activerecord/lib/active_record/relation/spawn_methods.rb
@@ -58,9 +58,6 @@ module ActiveRecord
     #   Post.order('id asc').only(:where)         # discards the order condition
     #   Post.order('id asc').only(:where, :order) # uses the specified order
     def only(*onlies)
-      if onlies.any? { |o| o == :where }
-        onlies << :bind
-      end
       relation_with values.slice(*onlies)
     end
 
diff --git a/activerecord/lib/active_record/relation/where_clause.rb b/activerecord/lib/active_record/relation/where_clause.rb
new file mode 100644
index 0000000000..f9b9e640ec
--- /dev/null
+++ b/activerecord/lib/active_record/relation/where_clause.rb
@@ -0,0 +1,173 @@
+module ActiveRecord
+  class Relation
+    class WhereClause # :nodoc:
+      attr_reader :binds
+
+      delegate :any?, :empty?, to: :predicates
+
+      def initialize(predicates, binds)
+        @predicates = predicates
+        @binds = binds
+      end
+
+      def +(other)
+        WhereClause.new(
+          predicates + other.predicates,
+          binds + other.binds,
+        )
+      end
+
+      def merge(other)
+        WhereClause.new(
+          predicates_unreferenced_by(other) + other.predicates,
+          non_conflicting_binds(other) + other.binds,
+        )
+      end
+
+      def except(*columns)
+        WhereClause.new(
+          predicates_except(columns),
+          binds_except(columns),
+        )
+      end
+
+      def or(other)
+        if empty?
+          self
+        elsif other.empty?
+          other
+        else
+          WhereClause.new(
+            [ast.or(other.ast)],
+            binds + other.binds
+          )
+        end
+      end
+
+      def to_h(table_name = nil)
+        equalities = predicates.grep(Arel::Nodes::Equality)
+        if table_name
+          equalities = equalities.select do |node|
+            node.left.relation.name == table_name
+          end
+        end
+
+        binds = self.binds.map { |attr| [attr.name, attr.value] }.to_h
+
+        equalities.map { |node|
+          name = node.left.name
+          [name, binds.fetch(name.to_s) {
+            case node.right
+            when Array then node.right.map(&:val)
+            when Arel::Nodes::Casted, Arel::Nodes::Quoted
+              node.right.val
+            end
+          }]
+        }.to_h
+      end
+
+      def ast
+        Arel::Nodes::And.new(predicates_with_wrapped_sql_literals)
+      end
+
+      def ==(other)
+        other.is_a?(WhereClause) &&
+          predicates == other.predicates &&
+          binds == other.binds
+      end
+
+      def invert
+        WhereClause.new(inverted_predicates, binds)
+      end
+
+      def self.empty
+        new([], [])
+      end
+
+      protected
+
+      attr_reader :predicates
+
+      def referenced_columns
+        @referenced_columns ||= begin
+          equality_nodes = predicates.select { |n| equality_node?(n) }
+          Set.new(equality_nodes, &:left)
+        end
+      end
+
+      private
+
+      def predicates_unreferenced_by(other)
+        predicates.reject do |n|
+          equality_node?(n) && other.referenced_columns.include?(n.left)
+        end
+      end
+
+      def equality_node?(node)
+        node.respond_to?(:operator) && node.operator == :==
+      end
+
+      def non_conflicting_binds(other)
+        conflicts = referenced_columns & other.referenced_columns
+        conflicts.map! { |node| node.name.to_s }
+        binds.reject { |attr| conflicts.include?(attr.name) }
+      end
+
+      def inverted_predicates
+        predicates.map { |node| invert_predicate(node) }
+      end
+
+      def invert_predicate(node)
+        case node
+        when NilClass
+          raise ArgumentError, 'Invalid argument for .where.not(), got nil.'
+        when Arel::Nodes::In
+          Arel::Nodes::NotIn.new(node.left, node.right)
+        when Arel::Nodes::Equality
+          Arel::Nodes::NotEqual.new(node.left, node.right)
+        when String
+          Arel::Nodes::Not.new(Arel::Nodes::SqlLiteral.new(node))
+        else
+          Arel::Nodes::Not.new(node)
+        end
+      end
+
+      def predicates_except(columns)
+        predicates.reject do |node|
+          case node
+          when Arel::Nodes::Between, Arel::Nodes::In, Arel::Nodes::NotIn, Arel::Nodes::Equality, Arel::Nodes::NotEqual, Arel::Nodes::LessThanOrEqual, Arel::Nodes::GreaterThanOrEqual
+            subrelation = (node.left.kind_of?(Arel::Attributes::Attribute) ? node.left : node.right)
+            columns.include?(subrelation.name.to_s)
+          end
+        end
+      end
+
+      def binds_except(columns)
+        binds.reject do |attr|
+          columns.include?(attr.name)
+        end
+      end
+
+      def predicates_with_wrapped_sql_literals
+        non_empty_predicates.map do |node|
+          if Arel::Nodes::Equality === node
+            node
+          else
+            wrap_sql_literal(node)
+          end
+        end
+      end
+
+      def non_empty_predicates
+        predicates - ['']
+      end
+
+      def wrap_sql_literal(node)
+        if ::String === node
+          node = Arel.sql(node)
+        end
+        Arel::Nodes::Grouping.new(node)
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/relation/where_clause_factory.rb b/activerecord/lib/active_record/relation/where_clause_factory.rb
new file mode 100644
index 0000000000..0430922be3
--- /dev/null
+++ b/activerecord/lib/active_record/relation/where_clause_factory.rb
@@ -0,0 +1,34 @@
+module ActiveRecord
+  class Relation
+    class WhereClauseFactory
+      def initialize(klass, predicate_builder)
+        @klass = klass
+        @predicate_builder = predicate_builder
+      end
+
+      def build(opts, other)
+        binds = []
+
+        case opts
+        when String, Array
+          parts = [klass.send(:sanitize_sql, other.empty? ? opts : ([opts] + other))]
+        when Hash
+          attributes = predicate_builder.resolve_column_aliases(opts)
+          attributes = klass.send(:expand_hash_conditions_for_aggregates, attributes)
+
+          attributes, binds = predicate_builder.create_binds(attributes)
+
+          parts = predicate_builder.build_from_hash(attributes)
+        else
+          parts = [opts]
+        end
+
+        WhereClause.new(parts, binds)
+      end
+
+      protected
+
+      attr_reader :klass, :predicate_builder
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/sanitization.rb b/activerecord/lib/active_record/sanitization.rb
index f5aa60a69a..313e767dcb 100644
--- a/activerecord/lib/active_record/sanitization.rb
+++ b/activerecord/lib/active_record/sanitization.rb
@@ -3,14 +3,11 @@ module ActiveRecord
     extend ActiveSupport::Concern
 
     module ClassMethods
-      def quote_value(value, column) #:nodoc:
-        connection.quote(value, column)
-      end
-
       # Used to sanitize objects before they're used in an SQL SELECT statement. Delegates to <tt>connection.quote</tt>.
       def sanitize(object) #:nodoc:
         connection.quote(object)
       end
+      alias_method :quote_value, :sanitize
 
       protected
 
@@ -72,35 +69,6 @@ module ActiveRecord
         expanded_attrs
       end
 
-      # Sanitizes a hash of attribute/value pairs into SQL conditions for a WHERE clause.
-      #   { name: "foo'bar", group_id: 4 }
-      #     # => "name='foo''bar' and group_id= 4"
-      #   { status: nil, group_id: [1,2,3] }
-      #     # => "status IS NULL and group_id IN (1,2,3)"
-      #   { age: 13..18 }
-      #     # => "age BETWEEN 13 AND 18"
-      #   { 'other_records.id' => 7 }
-      #     # => "`other_records`.`id` = 7"
-      #   { other_records: { id: 7 } }
-      #     # => "`other_records`.`id` = 7"
-      # And for value objects on a composed_of relationship:
-      #   { address: Address.new("123 abc st.", "chicago") }
-      #     # => "address_street='123 abc st.' and address_city='chicago'"
-      def sanitize_sql_hash_for_conditions(attrs, default_table_name = self.table_name)
-        table = Arel::Table.new(table_name).alias(default_table_name)
-        predicate_builder = PredicateBuilder.new(TableMetadata.new(self, table))
-        ActiveSupport::Deprecation.warn(<<-EOWARN)
-sanitize_sql_hash_for_conditions is deprecated, and will be removed in Rails 5.0
-        EOWARN
-        attrs = predicate_builder.resolve_column_aliases(attrs)
-        attrs = expand_hash_conditions_for_aggregates(attrs)
-
-        predicate_builder.build_from_hash(attrs).map { |b|
-          connection.visitor.compile b
-        }.join(' AND ')
-      end
-      alias_method :sanitize_sql_hash, :sanitize_sql_hash_for_conditions
-
       # Sanitizes a hash of attribute/value pairs into SQL conditions for a SET clause.
       #   { status: nil, group_id: 1 }
       #     # => "status = NULL , group_id = 1"
@@ -185,7 +153,7 @@ sanitize_sql_hash_for_conditions is deprecated, and will be removed in Rails 5.0
 
     # TODO: Deprecate this
     def quoted_id
-      self.class.quote_value(id, column_for_attribute(self.class.primary_key))
+      self.class.quote_value(@attributes[self.class.primary_key].value_for_database)
     end
   end
 end
diff --git a/activerecord/lib/active_record/secure_token.rb b/activerecord/lib/active_record/secure_token.rb
new file mode 100644
index 0000000000..07031b6371
--- /dev/null
+++ b/activerecord/lib/active_record/secure_token.rb
@@ -0,0 +1,39 @@
+module ActiveRecord
+  module SecureToken
+    extend ActiveSupport::Concern
+
+    module ClassMethods
+      # Example using has_secure_token
+      #
+      #   # Schema: User(token:string, auth_token:string)
+      #   class User < ActiveRecord::Base
+      #     has_secure_token
+      #     has_secure_token :auth_token
+      #   end
+      #
+      #   user = User.new
+      #   user.save
+      #   user.token # => "4kUgL2pdQMSCQtjE"
+      #   user.auth_token # => "77TMHrHJFvFDwodq8w7Ev2m7"
+      #   user.regenerate_token # => true
+      #   user.regenerate_auth_token # => true
+      #
+      # SecureRandom::base58 is used to generate the 24-character unique token, so collisions are highly unlikely.
+      #
+      # Note that it's still possible to generate a race condition in the database in the same way that
+      # validates_presence_of can. You're encouraged to add a unique index in the database to deal with
+      # this even more unlikely scenario.
+      def has_secure_token(attribute = :token)
+        # Load securerandom only when has_secure_token is used.
+        require 'active_support/core_ext/securerandom'
+        define_method("regenerate_#{attribute}") { update! attribute => self.class.generate_unique_secure_token }
+        before_create { self.send("#{attribute}=", self.class.generate_unique_secure_token) }
+      end
+
+      def generate_unique_secure_token
+        SecureRandom.base58(24)
+      end
+    end
+  end
+end
+
diff --git a/activerecord/lib/active_record/serializers/xml_serializer.rb b/activerecord/lib/active_record/serializers/xml_serializer.rb
index c2484d02ed..89b7e0be82 100644
--- a/activerecord/lib/active_record/serializers/xml_serializer.rb
+++ b/activerecord/lib/active_record/serializers/xml_serializer.rb
@@ -180,9 +180,9 @@ module ActiveRecord #:nodoc:
     class Attribute < ActiveModel::Serializers::Xml::Serializer::Attribute #:nodoc:
       def compute_type
         klass = @serializable.class
-        column = klass.columns_hash[name] || Type::Value.new
+        cast_type = klass.type_for_attribute(name)
 
-        type = ActiveSupport::XmlMini::TYPE_NAMES[value.class.name] || column.type
+        type = ActiveSupport::XmlMini::TYPE_NAMES[value.class.name] || cast_type.type
 
         { :text => :string,
           :time => :datetime }[type] || type
diff --git a/activerecord/lib/active_record/statement_cache.rb b/activerecord/lib/active_record/statement_cache.rb
index 192a19f05d..95986c820c 100644
--- a/activerecord/lib/active_record/statement_cache.rb
+++ b/activerecord/lib/active_record/statement_cache.rb
@@ -47,8 +47,8 @@ module ActiveRecord
 
       def sql_for(binds, connection)
         val = @values.dup
-        binds = binds.dup
-        @indexes.each { |i| val[i] = connection.quote(*binds.shift.reverse) }
+        binds = connection.prepare_binds_for_database(binds)
+        @indexes.each { |i| val[i] = connection.quote(binds.shift) }
         val.join
       end
     end
@@ -67,21 +67,21 @@ module ActiveRecord
     end
 
     class BindMap # :nodoc:
-      def initialize(bind_values)
+      def initialize(bound_attributes)
         @indexes   = []
-        @bind_values = bind_values
+        @bound_attributes = bound_attributes
 
-        bind_values.each_with_index do |(_, value), i|
-          if Substitute === value
+        bound_attributes.each_with_index do |attr, i|
+          if Substitute === attr.value
             @indexes << i
           end
         end
       end
 
       def bind(values)
-        bvs = @bind_values.map(&:dup)
-        @indexes.each_with_index { |offset,i| bvs[offset][1] = values[i] }
-        bvs
+        bas = @bound_attributes.dup
+        @indexes.each_with_index { |offset,i| bas[offset] = bas[offset].with_cast_value(values[i]) }
+        bas
       end
     end
 
@@ -89,7 +89,7 @@ module ActiveRecord
 
     def self.create(connection, block = Proc.new)
       relation      = block.call Params.new
-      bind_map      = BindMap.new relation.bind_values
+      bind_map      = BindMap.new relation.bound_attributes
       query_builder = connection.cacheable_query relation.arel
       new query_builder, bind_map
     end
diff --git a/activerecord/lib/active_record/table_metadata.rb b/activerecord/lib/active_record/table_metadata.rb
index 11e33e8dfe..6c8792ee80 100644
--- a/activerecord/lib/active_record/table_metadata.rb
+++ b/activerecord/lib/active_record/table_metadata.rb
@@ -22,6 +22,14 @@ module ActiveRecord
       arel_table[column_name]
     end
 
+    def type(column_name)
+      if klass
+        klass.type_for_attribute(column_name.to_s)
+      else
+        Type::Value.new
+      end
+    end
+
     def associated_with?(association_name)
       klass && klass._reflect_on_association(association_name)
     end
@@ -34,7 +42,7 @@ module ActiveRecord
         association_klass = association.klass
         arel_table = association_klass.arel_table
       else
-        type_caster = TypeCaster::Connection.new(klass.connection, table_name)
+        type_caster = TypeCaster::Connection.new(klass, table_name)
         association_klass = nil
         arel_table = Arel::Table.new(table_name, type_caster: type_caster)
       end
diff --git a/activerecord/lib/active_record/transactions.rb b/activerecord/lib/active_record/transactions.rb
index de701edca0..0fd2862b2c 100644
--- a/activerecord/lib/active_record/transactions.rb
+++ b/activerecord/lib/active_record/transactions.rb
@@ -4,24 +4,10 @@ module ActiveRecord
     extend ActiveSupport::Concern
     #:nodoc:
     ACTIONS = [:create, :destroy, :update]
-    #:nodoc:
-    CALLBACK_WARN_MESSAGE = "Currently, Active Record suppresses errors raised " \
-      "within `after_rollback`/`after_commit` callbacks and only print them to " \
-      "the logs. In the next version, these errors will no longer be suppressed. " \
-      "Instead, the errors will propagate normally just like in other Active " \
-      "Record callbacks.\n" \
-      "\n" \
-      "You can opt into the new behavior and remove this warning by setting:\n" \
-      "\n" \
-      "  config.active_record.raise_in_transactional_callbacks = true\n\n"
 
     included do
       define_callbacks :commit, :rollback,
-                       terminator: ->(_, result) { result == false },
                        scope: [:kind, :name]
-
-      mattr_accessor :raise_in_transactional_callbacks, instance_writer: false
-      self.raise_in_transactional_callbacks = false
     end
 
     # = Active Record Transactions
@@ -237,9 +223,6 @@ module ActiveRecord
       def after_commit(*args, &block)
         set_options_for_callbacks!(args)
         set_callback(:commit, :after, *args, &block)
-        unless ActiveRecord::Base.raise_in_transactional_callbacks
-          ActiveSupport::Deprecation.warn(CALLBACK_WARN_MESSAGE)
-        end
       end
 
       # This callback is called after a create, update, or destroy are rolled back.
@@ -248,9 +231,16 @@ module ActiveRecord
       def after_rollback(*args, &block)
         set_options_for_callbacks!(args)
         set_callback(:rollback, :after, *args, &block)
-        unless ActiveRecord::Base.raise_in_transactional_callbacks
-          ActiveSupport::Deprecation.warn(CALLBACK_WARN_MESSAGE)
-        end
+      end
+
+      def raise_in_transactional_callbacks
+        ActiveSupport::Deprecation.warn('ActiveRecord::Base.raise_in_transactional_callbacks is deprecated and will be removed without replacement.')
+        true
+      end
+
+      def raise_in_transactional_callbacks=(value)
+        ActiveSupport::Deprecation.warn('ActiveRecord::Base.raise_in_transactional_callbacks= is deprecated, has no effect and will be removed without replacement.')
+        value
       end
 
       private
@@ -310,7 +300,7 @@ module ActiveRecord
     #
     # Ensure that it is not called if the object was never persisted (failed create),
     # but call it after the commit of a destroyed object.
-    def committed!(should_run_callbacks = true) #:nodoc:
+    def committed!(should_run_callbacks: true) #:nodoc:
       _run_commit_callbacks if should_run_callbacks && destroyed? || persisted?
     ensure
       force_clear_transaction_record_state
@@ -318,7 +308,7 @@ module ActiveRecord
 
     # Call the +after_rollback+ callbacks. The +force_restore_state+ argument indicates if the record
     # state should be rolled back to the beginning or just to the last savepoint.
-    def rolledback!(force_restore_state = false, should_run_callbacks = true) #:nodoc:
+    def rolledback!(force_restore_state: false, should_run_callbacks: true) #:nodoc:
       _run_rollback_callbacks if should_run_callbacks
     ensure
       restore_transaction_record_state(force_restore_state)
@@ -388,7 +378,7 @@ module ActiveRecord
           thaw unless restore_state[:frozen?]
           @new_record = restore_state[:new_record]
           @destroyed  = restore_state[:destroyed]
-          write_attribute(self.class.primary_key, restore_state[:id])
+          write_attribute(self.class.primary_key, restore_state[:id]) if self.class.primary_key
         end
       end
     end
diff --git a/activerecord/lib/active_record/type/boolean.rb b/activerecord/lib/active_record/type/boolean.rb
index 978d16d524..f6a75512fd 100644
--- a/activerecord/lib/active_record/type/boolean.rb
+++ b/activerecord/lib/active_record/type/boolean.rb
@@ -10,19 +10,8 @@ module ActiveRecord
       def cast_value(value)
         if value == ''
           nil
-        elsif ConnectionAdapters::Column::TRUE_VALUES.include?(value)
-          true
         else
-          if !ConnectionAdapters::Column::FALSE_VALUES.include?(value)
-            ActiveSupport::Deprecation.warn(<<-MSG.squish)
-              You attempted to assign a value which is not explicitly `true` or `false`
-              to a boolean column. Currently this value casts to `false`. This will
-              change to match Ruby's semantics, and will cast to `true` in Rails 5.
-              If you would like to maintain the current behavior, you should
-              explicitly handle the values you would like cast to `false`.
-            MSG
-          end
-          false
+          !ConnectionAdapters::Column::FALSE_VALUES.include?(value)
         end
       end
     end
diff --git a/activerecord/lib/active_record/type/integer.rb b/activerecord/lib/active_record/type/integer.rb
index fc260a081a..90ca9f88da 100644
--- a/activerecord/lib/active_record/type/integer.rb
+++ b/activerecord/lib/active_record/type/integer.rb
@@ -3,6 +3,10 @@ module ActiveRecord
     class Integer < Value # :nodoc:
       include Numeric
 
+      # Column storage size in bytes.
+      # 4 bytes means a MySQL int or Postgres integer as opposed to smallint etc.
+      DEFAULT_LIMIT = 4
+
       def initialize(*)
         super
         @range = min_value...max_value
@@ -12,13 +16,19 @@ module ActiveRecord
         :integer
       end
 
-      alias type_cast_for_database type_cast
-
       def type_cast_from_database(value)
         return if value.nil?
         value.to_i
       end
 
+      def type_cast_for_database(value)
+        result = type_cast(value)
+        if result
+          ensure_in_range(result)
+        end
+        result
+      end
+
       protected
 
       attr_reader :range
@@ -30,20 +40,18 @@ module ActiveRecord
         when true then 1
         when false then 0
         else
-          result = value.to_i rescue nil
-          ensure_in_range(result) if result
-          result
+          value.to_i rescue nil
         end
       end
 
       def ensure_in_range(value)
         unless range.cover?(value)
-          raise RangeError, "#{value} is out of range for #{self.class} with limit #{limit || 4}"
+          raise RangeError, "#{value} is out of range for #{self.class} with limit #{limit || DEFAULT_LIMIT}"
         end
       end
 
       def max_value
-        limit = self.limit || 4
+        limit = self.limit || DEFAULT_LIMIT
         1 << (limit * 8 - 1) # 8 bits per byte with one bit for sign
       end
 
diff --git a/activerecord/lib/active_record/type/time.rb b/activerecord/lib/active_record/type/time.rb
index 41f7d97f0c..cab1c7bf1e 100644
--- a/activerecord/lib/active_record/type/time.rb
+++ b/activerecord/lib/active_record/type/time.rb
@@ -7,6 +7,19 @@ module ActiveRecord
         :time
       end
 
+      def user_input_in_time_zone(value)
+        return unless value.present?
+
+        case value
+        when ::String
+          value = "2000-01-01 #{value}"
+        when ::Time
+          value = value.change(year: 2000, day: 1, month: 1)
+        end
+
+        super(value)
+      end
+
       private
 
       def cast_value(value)
diff --git a/activerecord/lib/active_record/type/time_value.rb b/activerecord/lib/active_record/type/time_value.rb
index d611d72dd4..8d9ac25643 100644
--- a/activerecord/lib/active_record/type/time_value.rb
+++ b/activerecord/lib/active_record/type/time_value.rb
@@ -9,6 +9,10 @@ module ActiveRecord
         "'#{value.to_s(:db)}'"
       end
 
+      def user_input_in_time_zone(value)
+        value.in_time_zone
+      end
+
       private
 
       def new_time(year, mon, mday, hour, min, sec, microsec, offset = nil)
diff --git a/activerecord/lib/active_record/type/value.rb b/activerecord/lib/active_record/type/value.rb
index 60ae47db3d..859b51ca90 100644
--- a/activerecord/lib/active_record/type/value.rb
+++ b/activerecord/lib/active_record/type/value.rb
@@ -3,8 +3,7 @@ module ActiveRecord
     class Value # :nodoc:
       attr_reader :precision, :scale, :limit
 
-      # Valid options are +precision+, +scale+, and +limit+. They are only
-      # used when dumping schema.
+      # Valid options are +precision+, +scale+, and +limit+.
       def initialize(options = {})
         options.assert_valid_keys(:precision, :scale, :limit)
         @precision = options[:precision]
diff --git a/activerecord/lib/active_record/type_caster/connection.rb b/activerecord/lib/active_record/type_caster/connection.rb
index 9e4a130b40..3878270770 100644
--- a/activerecord/lib/active_record/type_caster/connection.rb
+++ b/activerecord/lib/active_record/type_caster/connection.rb
@@ -1,34 +1,29 @@
 module ActiveRecord
   module TypeCaster
     class Connection
-      def initialize(connection, table_name)
-        @connection = connection
+      def initialize(klass, table_name)
+        @klass = klass
         @table_name = table_name
       end
 
       def type_cast_for_database(attribute_name, value)
         return value if value.is_a?(Arel::Nodes::BindParam)
-        type = type_for(attribute_name)
-        type.type_cast_for_database(value)
+        column = column_for(attribute_name)
+        connection.type_cast_from_column(column, value)
       end
 
       protected
 
-      attr_reader :connection, :table_name
+      attr_reader :table_name
+      delegate :connection, to: :@klass
 
       private
 
-      def type_for(attribute_name)
+      def column_for(attribute_name)
         if connection.schema_cache.table_exists?(table_name)
-          column_for(attribute_name).cast_type
-        else
-          Type::Value.new
+          connection.schema_cache.columns_hash(table_name)[attribute_name.to_s]
         end
       end
-
-      def column_for(attribute_name)
-        connection.schema_cache.columns_hash(table_name)[attribute_name.to_s]
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/validations/uniqueness.rb b/activerecord/lib/active_record/validations/uniqueness.rb
index f52f91e89c..8f7a46f2c7 100644
--- a/activerecord/lib/active_record/validations/uniqueness.rb
+++ b/activerecord/lib/active_record/validations/uniqueness.rb
@@ -59,7 +59,8 @@ module ActiveRecord
         end
 
         column = klass.columns_hash[attribute_name]
-        value = klass.type_for_attribute(attribute_name).type_cast_for_database(value)
+        cast_type = klass.type_for_attribute(attribute_name)
+        value = cast_type.type_cast_for_database(value)
         value = klass.connection.type_cast(value)
         if value.is_a?(String) && column.limit
           value = value.to_s[0, column.limit]
@@ -67,7 +68,7 @@ module ActiveRecord
 
         value = Arel::Nodes::Quoted.new(value)
 
-        comparison = if !options[:case_sensitive] && value && column.text?
+        comparison = if !options[:case_sensitive] && value && cast_type.text?
           # will use SQL LOWER function before comparison, unless it detects a case insensitive collation
           klass.connection.case_insensitive_comparison(table, attribute, column, value)
         else