Merge branch 'master' into adequaterecord

* master: (311 commits)
  Add a missing changelog entry for #13981 and #14035
  Revert "Fixed plugin_generator test"
  implements new option :month_format_string for date select helpers [Closes #13618]
  add factory methods for empty alias trackers
  guarantee a list in the alias tracker so we can remove a conditional
  stop exposing table_joins
  make most parameters to the AliasTracker required
  make a singleton for AssociationScope
  pass the association and connection to the scope method
  pass the tracker down the stack and construct it in the scope method
  clean up add_constraints signature
  remove the reflection delegate
  remove klass delegator
  remove railties changes. fixes #14054
  remove chain delegate
  remove scope_chain delegate
  Add verb to sanitization note
  fix path shown in mailer's templates
  updated Travis build status image url
  fix guide active_support_core_extensions. add Note to String#indent [ci skip]
  ...

Conflicts:
	activerecord/lib/active_record/associations/join_dependency.rb
	activerecord/test/cases/associations/association_scope_test.rb

49 files changed, 626 insertions, 244 deletions

diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 714f623af3..142d21ce92 100644
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -130,7 +130,6 @@ module ActiveRecord
       autoload :JoinDependency,   'active_record/associations/join_dependency'
       autoload :AssociationScope, 'active_record/associations/association_scope'
       autoload :AliasTracker,     'active_record/associations/alias_tracker'
-      autoload :JoinHelper,       'active_record/associations/join_helper'
     end
 
     # Clears out the association cache.
@@ -669,11 +668,14 @@ module ActiveRecord
     # and member posts that use the posts table for STI. In this case, there must be a +type+
     # column in the posts table.
     #
+    # Note: The <tt>attachable_type=</tt> method is being called when assigning an +attachable+.
+    # The +class_name+ of the +attachable+ is passed as a String.
+    #
     #   class Asset < ActiveRecord::Base
     #     belongs_to :attachable, polymorphic: true
     #
-    #     def attachable_type=(sType)
-    #        super(sType.to_s.classify.constantize.base_class.to_s)
+    #     def attachable_type=(class_name)
+    #        super(class_name.constantize.base_class.to_s)
     #     end
     #   end
     #
@@ -1213,7 +1215,8 @@ module ActiveRecord
       #   Returns the associated object. +nil+ is returned if none is found.
       # [association=(associate)]
       #   Assigns the associate object, extracts the primary key, sets it as the foreign key,
-      #   and saves the associate object.
+      #   and saves the associate object. To avoid database inconsistencies, permanently deletes an existing
+      #   associated object when assigning a new one, even if the new one isn't saved to database.
       # [build_association(attributes = {})]
       #   Returns a new object of the associated type that has been instantiated
       #   with +attributes+ and linked to this object through a foreign key, but has not
@@ -1581,7 +1584,7 @@ module ActiveRecord
         hm_options[:through] = middle_reflection.name
         hm_options[:source] = join_model.right_reflection.name
 
-        [:before_add, :after_add, :before_remove, :after_remove].each do |k|
+        [:before_add, :after_add, :before_remove, :after_remove, :autosave].each do |k|
           hm_options[k] = options[k] if options.key? k
         end
 
diff --git a/activerecord/lib/active_record/associations/alias_tracker.rb b/activerecord/lib/active_record/associations/alias_tracker.rb
index 0c23029981..85109aee6c 100644
--- a/activerecord/lib/active_record/associations/alias_tracker.rb
+++ b/activerecord/lib/active_record/associations/alias_tracker.rb
@@ -5,16 +5,48 @@ module ActiveRecord
     # Keeps track of table aliases for ActiveRecord::Associations::ClassMethods::JoinDependency and
     # ActiveRecord::Associations::ThroughAssociationScope
     class AliasTracker # :nodoc:
-      attr_reader :aliases, :table_joins, :connection
+      attr_reader :aliases, :connection
+
+      def self.empty(connection)
+        new connection, Hash.new(0)
+      end
+
+      def self.create(connection, table_joins)
+        if table_joins.empty?
+          empty connection
+        else
+          aliases = Hash.new { |h,k|
+            h[k] = initial_count_for(connection, k, table_joins)
+          }
+          new connection, aliases
+        end
+      end
+
+      def self.initial_count_for(connection, name, table_joins)
+        # quoted_name should be downcased as some database adapters (Oracle) return quoted name in uppercase
+        quoted_name = connection.quote_table_name(name).downcase
+
+        counts = table_joins.map do |join|
+          if join.is_a?(Arel::Nodes::StringJoin)
+            # Table names + table aliases
+            join.left.downcase.scan(
+              /join(?:\s+\w+)?\s+(\S+\s+)?#{quoted_name}\son/
+            ).size
+          else
+            join.left.table_name == name ? 1 : 0
+          end
+        end
+
+        counts.sum
+      end
 
       # table_joins is an array of arel joins which might conflict with the aliases we assign here
-      def initialize(connection = Base.connection, table_joins = [])
-        @aliases     = Hash.new { |h,k| h[k] = initial_count_for(k) }
-        @table_joins = table_joins
-        @connection  = connection
+      def initialize(connection, aliases)
+        @aliases    = aliases
+        @connection = connection
       end
 
-      def aliased_table_for(table_name, aliased_name = nil)
+      def aliased_table_for(table_name, aliased_name)
         table_alias = aliased_name_for(table_name, aliased_name)
 
         if table_alias == table_name
@@ -24,9 +56,7 @@ module ActiveRecord
         end
       end
 
-      def aliased_name_for(table_name, aliased_name = nil)
-        aliased_name ||= table_name
-
+      def aliased_name_for(table_name, aliased_name)
         if aliases[table_name].zero?
           # If it's zero, we can have our table_name
           aliases[table_name] = 1
@@ -48,26 +78,6 @@ module ActiveRecord
 
       private
 
-        def initial_count_for(name)
-          return 0 if Arel::Table === table_joins
-
-          # quoted_name should be downcased as some database adapters (Oracle) return quoted name in uppercase
-          quoted_name = connection.quote_table_name(name).downcase
-
-          counts = table_joins.map do |join|
-            if join.is_a?(Arel::Nodes::StringJoin)
-              # Table names + table aliases
-              join.left.downcase.scan(
-                /join(?:\s+\w+)?\s+(\S+\s+)?#{quoted_name}\son/
-              ).size
-            else
-              join.left.table_name == name ? 1 : 0
-            end
-          end
-
-          counts.sum
-        end
-
         def truncate(name)
           name.slice(0, connection.table_alias_length - 2)
         end
diff --git a/activerecord/lib/active_record/associations/association.rb b/activerecord/lib/active_record/associations/association.rb
index 67ea489b22..4e46256862 100644
--- a/activerecord/lib/active_record/associations/association.rb
+++ b/activerecord/lib/active_record/associations/association.rb
@@ -94,7 +94,7 @@ module ActiveRecord
       # actually gets built.
       def association_scope
         if klass
-          @association_scope ||= AssociationScope.new(self).scope
+          @association_scope ||= AssociationScope.scope(self, klass.connection)
         end
       end
 
diff --git a/activerecord/lib/active_record/associations/association_scope.rb b/activerecord/lib/active_record/associations/association_scope.rb
index f455b6934e..bb889a8f3b 100644
--- a/activerecord/lib/active_record/associations/association_scope.rb
+++ b/activerecord/lib/active_record/associations/association_scope.rb
@@ -1,52 +1,77 @@
 module ActiveRecord
   module Associations
     class AssociationScope #:nodoc:
-      include JoinHelper
+      INSTANCE = new
 
-      attr_reader :association, :alias_tracker
+      def self.scope(association, connection)
+        INSTANCE.scope association, connection
+      end
 
-      delegate :klass, :owner, :reflection, :interpolate, :to => :association
-      delegate :chain, :scope_chain, :options, :source_options, :active_record, :to => :reflection
+      def scope(association, connection)
+        klass         = association.klass
+        reflection    = association.reflection
+        scope         = klass.unscoped
+        owner         = association.owner
+        alias_tracker = AliasTracker.empty connection
 
-      def initialize(association)
-        @association   = association
-        @alias_tracker = AliasTracker.new klass.connection
+        scope.extending! Array(reflection.options[:extend])
+        add_constraints(scope, owner, klass, reflection, alias_tracker)
       end
 
-      def scope
-        scope = klass.unscoped
-        scope.extending! Array(options[:extend])
-        add_constraints(scope)
+      def join_type
+        Arel::Nodes::InnerJoin
       end
 
       private
 
-      def column_for(table_name, column_name)
+      def construct_tables(chain, klass, refl, alias_tracker)
+        chain.map do |reflection|
+          alias_tracker.aliased_table_for(
+            table_name_for(reflection, klass, refl),
+            table_alias_for(reflection, refl, reflection != refl)
+          )
+        end
+      end
+
+      def table_alias_for(reflection, refl, join = false)
+        name = "#{reflection.plural_name}_#{alias_suffix(refl)}"
+        name << "_join" if join
+        name
+      end
+
+      def join(table, constraint)
+        table.create_join(table, table.create_on(constraint), join_type)
+      end
+
+      def column_for(table_name, column_name, alias_tracker)
         columns = alias_tracker.connection.schema_cache.columns_hash(table_name)
         columns[column_name]
       end
 
-      def bind_value(scope, column, value)
+      def bind_value(scope, column, value, alias_tracker)
         substitute = alias_tracker.connection.substitute_at(
           column, scope.bind_values.length)
         scope.bind_values += [[column, value]]
         substitute
       end
 
-      def bind(scope, table_name, column_name, value)
-        column   = column_for table_name, column_name
-        bind_value scope, column, value
+      def bind(scope, table_name, column_name, value, tracker)
+        column   = column_for table_name, column_name, tracker
+        bind_value scope, column, value, tracker
       end
 
-      def add_constraints(scope)
-        tables = construct_tables
+      def add_constraints(scope, owner, assoc_klass, refl, tracker)
+        chain = refl.chain
+        scope_chain = refl.scope_chain
+
+        tables = construct_tables(chain, assoc_klass, refl, tracker)
 
         chain.each_with_index do |reflection, i|
           table, foreign_table = tables.shift, tables.first
 
           if reflection.source_macro == :belongs_to
             if reflection.options[:polymorphic]
-              key = reflection.association_primary_key(self.klass)
+              key = reflection.association_primary_key(assoc_klass)
             else
               key = reflection.association_primary_key
             end
@@ -58,12 +83,12 @@ module ActiveRecord
           end
 
           if reflection == chain.last
-            bind_val = bind scope, table.table_name, key.to_s, owner[foreign_key]
+            bind_val = bind scope, table.table_name, key.to_s, owner[foreign_key], tracker
             scope    = scope.where(table[key].eq(bind_val))
 
             if reflection.type
               value    = owner.class.base_class.name
-              bind_val = bind scope, table.table_name, reflection.type.to_s, value
+              bind_val = bind scope, table.table_name, reflection.type.to_s, value, tracker
               scope    = scope.where(table[reflection.type].eq(bind_val))
             end
           else
@@ -71,7 +96,7 @@ module ActiveRecord
 
             if reflection.type
               value    = chain[i + 1].klass.base_class.name
-              bind_val = bind scope, table.table_name, reflection.type.to_s, value
+              bind_val = bind scope, table.table_name, reflection.type.to_s, value, tracker
               scope    = scope.where(table[reflection.type].eq(bind_val))
             end
 
@@ -79,14 +104,14 @@ module ActiveRecord
           end
 
           is_first_chain = i == 0
-          klass = is_first_chain ? self.klass : reflection.klass
+          klass = is_first_chain ? assoc_klass : reflection.klass
 
           # Exclude the scope of the association itself, because that
           # was already merged in the #scope method.
           scope_chain[i].each do |scope_chain_item|
-            item  = eval_scope(klass, scope_chain_item)
+            item  = eval_scope(klass, scope_chain_item, owner)
 
-            if scope_chain_item == self.reflection.scope
+            if scope_chain_item == refl.scope
               scope.merge! item.except(:where, :includes, :bind)
             end
 
@@ -103,22 +128,22 @@ module ActiveRecord
         scope
       end
 
-      def alias_suffix
-        reflection.name
+      def alias_suffix(refl)
+        refl.name
       end
 
-      def table_name_for(reflection)
-        if reflection == self.reflection
+      def table_name_for(reflection, klass, refl)
+        if reflection == refl
           # If this is a polymorphic belongs_to, we want to get the klass from the
           # association because it depends on the polymorphic_type attribute of
           # the owner
           klass.table_name
         else
-          super
+          reflection.table_name
         end
       end
 
-      def eval_scope(klass, scope)
+      def eval_scope(klass, scope, owner)
         if scope.is_a?(Relation)
           scope
         else
diff --git a/activerecord/lib/active_record/associations/builder/association.rb b/activerecord/lib/active_record/associations/builder/association.rb
index 3911d1b520..f085fd1cfd 100644
--- a/activerecord/lib/active_record/associations/builder/association.rb
+++ b/activerecord/lib/active_record/associations/builder/association.rb
@@ -26,6 +26,12 @@ module ActiveRecord::Associations::Builder
     attr_reader :name, :scope, :options
 
     def self.build(model, name, scope, options, &block)
+      if model.dangerous_attribute_method?(name)
+        raise ArgumentError, "You tried to define an association named #{name} on the model #{model.name}, but " \
+                             "this will conflict with a method #{name} already defined by Active Record. " \
+                             "Please choose a different association name."
+      end
+
       builder = create_builder model, name, scope, options, &block
       reflection = builder.build(model)
       define_accessors model, reflection
diff --git a/activerecord/lib/active_record/associations/collection_association.rb b/activerecord/lib/active_record/associations/collection_association.rb
index 52531a3520..03ca00fa70 100644
--- a/activerecord/lib/active_record/associations/collection_association.rb
+++ b/activerecord/lib/active_record/associations/collection_association.rb
@@ -24,6 +24,10 @@ module ActiveRecord
     # If you need to work on all current children, new and existing records,
     # +load_target+ and the +loaded+ flag are your friends.
     class CollectionAssociation < Association #:nodoc:
+      def initialize(owner, reflection)
+        super
+        @proxy = CollectionProxy.create(klass, self)
+      end
 
       # Implements the reader method, e.g. foo.items for Foo.has_many :items
       def reader(force_reload = false)
@@ -33,7 +37,7 @@ module ActiveRecord
           reload
         end
 
-        @proxy ||= CollectionProxy.create(klass, self)
+        @proxy
       end
 
       # Implements the writer method, e.g. foo.items= for Foo.has_many :items
@@ -96,11 +100,31 @@ module ActiveRecord
       end
 
       def first(*args)
-        first_or_last(:first, *args)
+        first_nth_or_last(:first, *args)
+      end
+
+      def second(*args)
+        first_nth_or_last(:second, *args)
+      end
+
+      def third(*args)
+        first_nth_or_last(:third, *args)
+      end
+
+      def fourth(*args)
+        first_nth_or_last(:fourth, *args)
+      end
+
+      def fifth(*args)
+        first_nth_or_last(:fifth, *args)
+      end
+
+      def forty_two(*args)
+        first_nth_or_last(:forty_two, *args)
       end
 
       def last(*args)
-        first_or_last(:last, *args)
+        first_nth_or_last(:last, *args)
       end
 
       def build(attributes = {}, &block)
@@ -526,7 +550,7 @@ module ActiveRecord
         #   * target already loaded
         #   * owner is new record
         #   * target contains new or changed record(s)
-        def fetch_first_or_last_using_find?(args)
+        def fetch_first_nth_or_last_using_find?(args)
           if args.first.is_a?(Hash)
             true
           else
@@ -564,10 +588,10 @@ module ActiveRecord
         end
 
         # Fetches the first/last using SQL if possible, otherwise from the target array.
-        def first_or_last(type, *args)
+        def first_nth_or_last(type, *args)
           args.shift if args.first.is_a?(Hash) && args.first.empty?
 
-          collection = fetch_first_or_last_using_find?(args) ? scope : load_target
+          collection = fetch_first_nth_or_last_using_find?(args) ? scope : load_target
           collection.send(type, *args).tap do |record|
             set_inverse_instance record if record.is_a? ActiveRecord::Base
           end
diff --git a/activerecord/lib/active_record/associations/collection_proxy.rb b/activerecord/lib/active_record/associations/collection_proxy.rb
index e3fc908444..eba688866c 100644
--- a/activerecord/lib/active_record/associations/collection_proxy.rb
+++ b/activerecord/lib/active_record/associations/collection_proxy.rb
@@ -84,7 +84,7 @@ module ActiveRecord
       #
       # Be careful because this also means you're initializing a model
       # object with only the fields that you've selected. If you attempt
-      # to access a field that is not in the initialized record you'll
+      # to access a field except +id+ that is not in the initialized record you'll
       # receive:
       #
       #   person.pets.select(:name).first.person_id
@@ -170,6 +170,32 @@ module ActiveRecord
         @association.first(*args)
       end
 
+      # Same as +first+ except returns only the second record.
+      def second(*args)
+        @association.second(*args)
+      end
+
+      # Same as +first+ except returns only the third record.
+      def third(*args)
+        @association.third(*args)
+      end
+
+      # Same as +first+ except returns only the fourth record.
+      def fourth(*args)
+        @association.fourth(*args)
+      end
+
+      # Same as +first+ except returns only the fifth record.
+      def fifth(*args)
+        @association.fifth(*args)
+      end
+
+      # Same as +first+ except returns only the forty second record.
+      # Also known as accessing "the reddit".
+      def forty_two(*args)
+        @association.forty_two(*args)
+      end
+
       # Returns the last record, or the last +n+ records, from the collection.
       # If the collection is empty, the first form returns +nil+, and the second
       # form returns an empty array.
@@ -978,6 +1004,28 @@ module ActiveRecord
         proxy_association.reload
         self
       end
+
+      # Unloads the association. Returns +self+.
+      #
+      #   class Person < ActiveRecord::Base
+      #     has_many :pets
+      #   end
+      #
+      #   person.pets # fetches pets from the database
+      #   # => [#<Pet id: 1, name: "Snoop", group: "dogs", person_id: 1>]
+      #
+      #   person.pets # uses the pets cache
+      #   # => [#<Pet id: 1, name: "Snoop", group: "dogs", person_id: 1>]
+      #
+      #   person.pets.reset # clears the pets cache
+      #
+      #   person.pets  # fetches pets from the database
+      #   # => [#<Pet id: 1, name: "Snoop", group: "dogs", person_id: 1>]
+      def reset
+        proxy_association.reset
+        proxy_association.reset_scope
+        self
+      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/associations/has_many_association.rb b/activerecord/lib/active_record/associations/has_many_association.rb
index 72e0891702..6457182195 100644
--- a/activerecord/lib/active_record/associations/has_many_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_association.rb
@@ -111,7 +111,7 @@ module ActiveRecord
             records.each(&:destroy!)
             update_counter(-records.length) unless inverse_updates_counter_cache?
           else
-            if records == :all
+            if records == :all || !reflection.klass.primary_key
               scope = self.scope
             else
               scope = self.scope.where(reflection.klass.primary_key => records)
diff --git a/activerecord/lib/active_record/associations/join_dependency.rb b/activerecord/lib/active_record/associations/join_dependency.rb
index b5f9ee6cee..b7dc037a65 100644
--- a/activerecord/lib/active_record/associations/join_dependency.rb
+++ b/activerecord/lib/active_record/associations/join_dependency.rb
@@ -93,8 +93,8 @@ module ActiveRecord
       #    joins # =>  []
       #
       def initialize(base, associations, joins)
-        @alias_tracker = AliasTracker.new(base.connection, joins)
-        @alias_tracker.aliased_name_for(base.table_name) # Updates the count for base.table_name to 1
+        @alias_tracker = AliasTracker.create(base.connection, joins)
+        @alias_tracker.aliased_name_for(base.table_name, base.table_name) # Updates the count for base.table_name to 1
         tree = self.class.make_tree associations
         @join_root = JoinBase.new base, build(tree, base)
         @join_root.children.each { |child| construct_tables! @join_root, child }
@@ -163,16 +163,16 @@ module ActiveRecord
 
       def make_outer_joins(parent, child)
         tables    = table_aliases_for(parent, child)
-        join_type = Arel::OuterJoin
-        info = make_constraints parent, child, tables, join_type
+        join_type = Arel::Nodes::OuterJoin
+        info      = make_constraints parent, child, tables, join_type
 
         [info] + child.children.flat_map { |c| make_outer_joins(child, c) }
       end
 
       def make_inner_joins(parent, child)
         tables    = child.tables
-        join_type = Arel::InnerJoin
-        info = make_constraints parent, child, tables, join_type
+        join_type = Arel::Nodes::InnerJoin
+        info      = make_constraints parent, child, tables, join_type
 
         [info] + child.children.flat_map { |c| make_inner_joins(child, c) }
       end
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 0333816abb..ca36462054 100644
--- a/activerecord/lib/active_record/associations/join_dependency/join_association.rb
+++ b/activerecord/lib/active_record/associations/join_dependency/join_association.rb
@@ -28,7 +28,8 @@ module ActiveRecord
           bind_values   = []
           tables        = tables.reverse
 
-          scope_chain_iter = scope_chain.reverse_each
+          scope_chain_index = 0
+          scope_chain = scope_chain.reverse
 
           # The chain starts with the target table, but we want to end with it here (makes
           # more sense in this context), so we reverse
@@ -47,13 +48,14 @@ module ActiveRecord
 
             constraint = build_constraint(klass, table, key, foreign_table, foreign_key)
 
-            scope_chain_items = scope_chain_iter.next.map do |item|
+            scope_chain_items = scope_chain[scope_chain_index].map do |item|
               if item.is_a?(Relation)
                 item
               else
                 ActiveRecord::Relation.create(klass, table).instance_exec(node, &item)
               end
             end
+            scope_chain_index += 1
 
             scope_chain_items.concat [klass.send(:build_default_scope)].compact
 
diff --git a/activerecord/lib/active_record/associations/join_helper.rb b/activerecord/lib/active_record/associations/join_helper.rb
deleted file mode 100644
index f345d16841..0000000000
--- a/activerecord/lib/active_record/associations/join_helper.rb
+++ /dev/null
@@ -1,36 +0,0 @@
-module ActiveRecord
-  module Associations
-    # Helper class module which gets mixed into JoinDependency::JoinAssociation and AssociationScope
-    module JoinHelper #:nodoc:
-
-      def join_type
-        Arel::InnerJoin
-      end
-
-      private
-
-      def construct_tables
-        chain.map do |reflection|
-          alias_tracker.aliased_table_for(
-            table_name_for(reflection),
-            table_alias_for(reflection, reflection != self.reflection)
-          )
-        end
-      end
-
-      def table_name_for(reflection)
-        reflection.table_name
-      end
-
-      def table_alias_for(reflection, join = false)
-        name = "#{reflection.plural_name}_#{alias_suffix}"
-        name << "_join" if join
-        name
-      end
-
-      def join(table, constraint)
-        table.create_join(table, table.create_on(constraint), join_type)
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/associations/singular_association.rb b/activerecord/lib/active_record/associations/singular_association.rb
index e4500af5b2..399aff378a 100644
--- a/activerecord/lib/active_record/associations/singular_association.rb
+++ b/activerecord/lib/active_record/associations/singular_association.rb
@@ -39,7 +39,7 @@ module ActiveRecord
         end
 
         def find_target
-          if record = scope.first
+          if record = scope.take
             set_inverse_instance record
           end
         end
diff --git a/activerecord/lib/active_record/attribute_methods.rb b/activerecord/lib/active_record/attribute_methods.rb
index 73761520f7..9326c9c117 100644
--- a/activerecord/lib/active_record/attribute_methods.rb
+++ b/activerecord/lib/active_record/attribute_methods.rb
@@ -110,16 +110,34 @@ module ActiveRecord
         end
       end
 
-      # A method name is 'dangerous' if it is already defined by Active Record, but
+      # A method name is 'dangerous' if it is already (re)defined by Active Record, but
       # not by any ancestors. (So 'puts' is not dangerous but 'save' is.)
       def dangerous_attribute_method?(name) # :nodoc:
         method_defined_within?(name, Base)
       end
 
-      def method_defined_within?(name, klass, sup = klass.superclass) # :nodoc:
+      def method_defined_within?(name, klass, superklass = klass.superclass) # :nodoc:
         if klass.method_defined?(name) || klass.private_method_defined?(name)
-          if sup.method_defined?(name) || sup.private_method_defined?(name)
-            klass.instance_method(name).owner != sup.instance_method(name).owner
+          if superklass.method_defined?(name) || superklass.private_method_defined?(name)
+            klass.instance_method(name).owner != superklass.instance_method(name).owner
+          else
+            true
+          end
+        else
+          false
+        end
+      end
+
+      # A class method is 'dangerous' if it is already (re)defined by Active Record, but
+      # not by any ancestors. (So 'puts' is not dangerous but 'new' is.)
+      def dangerous_class_method?(method_name)
+        class_method_defined_within?(method_name, Base)
+      end
+
+      def class_method_defined_within?(name, klass, superklass = klass.superclass) # :nodoc
+        if klass.respond_to?(name, true)
+          if superklass.respond_to?(name, true)
+            klass.method(name).owner != superklass.method(name).owner
           else
             true
           end
@@ -260,6 +278,11 @@ module ActiveRecord
       }
     end
 
+    # Placeholder so it can be overriden when needed by serialization
+    def attributes_for_coder # :nodoc:
+      attributes
+    end
+
     # Returns an <tt>#inspect</tt>-like string for the value of the
     # attribute +attr_name+. String attributes are truncated upto 50
     # characters, Date and Time attributes are returned in the
diff --git a/activerecord/lib/active_record/attribute_methods/dirty.rb b/activerecord/lib/active_record/attribute_methods/dirty.rb
index 19e81abba5..8a1b199997 100644
--- a/activerecord/lib/active_record/attribute_methods/dirty.rb
+++ b/activerecord/lib/active_record/attribute_methods/dirty.rb
@@ -38,11 +38,37 @@ module ActiveRecord
         end
       end
 
+    def initialize_dup(other) # :nodoc:
+      super
+      init_changed_attributes
+    end
+
     private
+      def initialize_internals_callback
+        super
+        init_changed_attributes
+      end
+
+      def init_changed_attributes
+        @changed_attributes = nil
+        # Intentionally avoid using #column_defaults since overridden defaults (as is done in
+        # optimistic locking) won't get written unless they get marked as changed
+        self.class.columns.each do |c|
+          attr, orig_value = c.name, c.default
+          changed_attributes[attr] = orig_value if _field_changed?(attr, orig_value, @attributes[attr])
+        end
+      end
+
       # Wrap write_attribute to remember original attribute value.
       def write_attribute(attr, value)
         attr = attr.to_s
 
+        save_changed_attribute(attr, value)
+
+        super(attr, value)
+      end
+
+      def save_changed_attribute(attr, value)
         # The attribute already has an unsaved change.
         if attribute_changed?(attr)
           old = changed_attributes[attr]
@@ -51,9 +77,6 @@ module ActiveRecord
           old = clone_attribute_value(:read_attribute, attr)
           changed_attributes[attr] = old if _field_changed?(attr, old, value)
         end
-
-        # Carry on.
-        super(attr, value)
       end
 
       def update_record(*)
@@ -67,7 +90,7 @@ module ActiveRecord
       # Serialized attributes should always be written in case they've been
       # changed in place.
       def keys_for_partial_write
-        changed | (attributes.keys & self.class.serialized_attributes.keys)
+        changed
       end
 
       def _field_changed?(attr, old, value)
diff --git a/activerecord/lib/active_record/attribute_methods/serialization.rb b/activerecord/lib/active_record/attribute_methods/serialization.rb
index d484659190..67abbbc2a0 100644
--- a/activerecord/lib/active_record/attribute_methods/serialization.rb
+++ b/activerecord/lib/active_record/attribute_methods/serialization.rb
@@ -115,6 +115,14 @@ module ActiveRecord
           end
         end
 
+        def should_record_timestamps?
+          super || (self.record_timestamps && (attributes.keys & self.class.serialized_attributes.keys).present?)
+        end
+
+        def keys_for_partial_write
+          super | (attributes.keys & self.class.serialized_attributes.keys)
+        end
+
         def type_cast_attribute_for_write(column, value)
           if column && coder = self.class.serialized_attributes[column.name]
             Attribute.new(coder, value, :unserialized)
@@ -156,6 +164,16 @@ module ActiveRecord
             super
           end
         end
+
+        def attributes_for_coder
+          attribute_names.each_with_object({}) do |name, attrs|
+            attrs[name] = if self.class.serialized_attributes.include?(name)
+                            @attributes[name].serialized_value
+                          else
+                            read_attribute(name)
+                          end
+          end
+        end
       end
     end
   end
diff --git a/activerecord/lib/active_record/autosave_association.rb b/activerecord/lib/active_record/autosave_association.rb
index e9622ca0c1..4f58d06f35 100644
--- a/activerecord/lib/active_record/autosave_association.rb
+++ b/activerecord/lib/active_record/autosave_association.rb
@@ -301,7 +301,7 @@ module ActiveRecord
       def association_valid?(reflection, record)
         return true if record.destroyed? || record.marked_for_destruction?
 
-        unless valid = record.valid?
+        unless valid = record.valid?(self.validation_context)
           if reflection.options[:autosave]
             record.errors.each do |attribute, message|
               attribute = "#{reflection.name}.#{attribute}"
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 1d3ec75aa1..9ec1feea97 100644
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -294,6 +294,7 @@ module ActiveRecord #:nodoc:
     extend Enum
     extend Delegation::DelegateCache
 
+    include Core
     include Persistence
     include NoTouching
     include ReadonlyAttributes
@@ -320,7 +321,6 @@ module ActiveRecord #:nodoc:
     include Reflection
     include Serialization
     include Store
-    include Core
   end
 
   ActiveSupport.run_load_hooks(:active_record, Base)
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 cebe741daa..759e162e19 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
@@ -393,7 +393,7 @@ module ActiveRecord
         synchronize do
           stale = Time.now - @dead_connection_timeout
           connections.dup.each do |conn|
-            if conn.in_use? && stale > conn.last_use && !conn.active?
+            if conn.in_use? && stale > conn.last_use && !conn.active_threadsafe?
               remove conn
             end
           end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
index cc108a3a61..9371d6f992 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
@@ -26,6 +26,14 @@ module ActiveRecord
 
       # Returns an ActiveRecord::Result instance.
       def select_all(arel, name = nil, binds = [])
+        if arel.is_a?(Relation)
+          relation = arel
+          arel = relation.arel
+          if !binds || binds.empty?
+            binds = relation.bind_values
+          end
+        end
+
         select(to_sql(arel, binds), name, binds)
       end
 
@@ -45,13 +53,16 @@ module ActiveRecord
       # Returns an array of the values of the first column in a select:
       #   select_values("SELECT id FROM companies LIMIT 3") => [1,2,3]
       def select_values(arel, name = nil)
-        select_rows(to_sql(arel, []), name)
-          .map { |v| v[0] }
+        binds = []
+        if arel.is_a?(Relation)
+          arel, binds = arel.arel, arel.bind_values
+        end
+        select_rows(to_sql(arel, binds), name, binds).map(&:first)
       end
 
       # Returns an array of arrays containing the field values.
       # Order is the same as that returned by +columns+.
-      def select_rows(sql, name = nil)
+      def select_rows(sql, name = nil, binds = [])
       end
       undef_method :select_rows
 
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 88bf15bc18..ad069f5e53 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -120,9 +120,9 @@ module ActiveRecord
       #   The name of the primary key, if one is to be added automatically.
       #   Defaults to +id+. If <tt>:id</tt> is false this option is ignored.
       #
-      #   Also note that this just sets the primary key in the table. You additionally
-      #   need to configure the primary key in the model via +self.primary_key=+.
-      #   Models do NOT auto-detect the primary key from their table definition.
+      #   Note that Active Record models will automatically detect their
+      #   primary key. This can be avoided by using +self.primary_key=+ on the model
+      #   to define the key explicitly.
       #
       # [<tt>:options</tt>]
       #   Any extra options you want appended to the table definition.
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb b/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb
index 2b6685499a..bc4884b538 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb
@@ -23,6 +23,10 @@ module ActiveRecord
         @parent = nil
       end
 
+      def finalized?
+        @state
+      end
+
       def committed?
         @state == :committed
       end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index a8a530e1d5..2ba028e658 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -266,6 +266,12 @@ module ActiveRecord
       def active?
       end
 
+      # Adapter should redefine this if it needs a threadsafe way to approximate
+      # if the connection is active
+      def active_threadsafe?
+        active?
+      end
+
       # Disconnects from the database if already connected, and establishes a
       # new connection with the database. Implementors should call super if they
       # override the default implementation.
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 7768c24967..23edc8b955 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -298,11 +298,7 @@ module ActiveRecord
 
       # Executes the SQL statement in the context of this connection.
       def execute(sql, name = nil)
-        if name == :skip_logging
-          @connection.query(sql)
-        else
-          log(sql, name) { @connection.query(sql) }
-        end
+        log(sql, name) { @connection.query(sql) }
       end
 
       # MysqlAdapter has to free a result after using it, so we use this method to write
@@ -775,7 +771,7 @@ module ActiveRecord
         end.compact.join(', ')
 
         # ...and send them all in one query
-        execute("SET #{encoding} #{variable_assignments}", :skip_logging)
+        @connection.query  "SET #{encoding} #{variable_assignments}"
       end
     end
   end
diff --git a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
index 830b1be021..69c2a361ee 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
@@ -217,7 +217,7 @@ module ActiveRecord
 
       # Returns an array of arrays containing the field values.
       # Order is the same as that returned by +columns+.
-      def select_rows(sql, name = nil)
+      def select_rows(sql, name = nil, binds = [])
         execute(sql, name).to_a
       end
 
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index 7dbaa272a3..49f0bfbcde 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -213,9 +213,9 @@ module ActiveRecord
 
       # DATABASE STATEMENTS ======================================
 
-      def select_rows(sql, name = nil)
+      def select_rows(sql, name = nil, binds = [])
         @connection.query_with_result = true
-        rows = exec_query(sql, name).rows
+        rows = exec_query(sql, name, binds).rows
         @connection.more_results && @connection.next_result    # invoking stored procedures with CLIENT_MULTI_RESULTS requires this to tidy up else connection will be dropped
         rows
       end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/array_parser.rb b/activerecord/lib/active_record/connection_adapters/postgresql/array_parser.rb
index 20de8d1982..0b218f2bfd 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/array_parser.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/array_parser.rb
@@ -91,8 +91,9 @@ module ActiveRecord
           end
 
           def add_item_to_array(array, current_item, quoted)
-            if current_item.length == 0
-            elsif !quoted && current_item == 'NULL'
+            return if !quoted && current_item.length == 0
+
+            if !quoted && current_item == 'NULL'
               array.push nil
             else
               array.push current_item
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
index f349c37724..51ee2829b2 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
@@ -46,8 +46,8 @@ module ActiveRecord
 
         # Executes a SELECT query and returns an array of rows. Each row is an
         # array of field values.
-        def select_rows(sql, name = nil)
-          select_raw(sql, name).last
+        def select_rows(sql, name = nil, binds = [])
+          exec_query(sql, name, binds).rows
         end
 
         # Executes an INSERT query and returns the new record's ID
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 571257f6dd..ae8ede4b42 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
@@ -126,6 +126,19 @@ module ActiveRecord
           SQL
         end
 
+        def index_name_exists?(table_name, index_name, default)
+          exec_query(<<-SQL, 'SCHEMA').rows.first[0].to_i > 0
+            SELECT COUNT(*)
+            FROM pg_class t
+            INNER JOIN pg_index d ON t.oid = d.indrelid
+            INNER JOIN pg_class i ON d.indexrelid = i.oid
+            WHERE i.relkind = 'i'
+              AND i.relname = '#{index_name}'
+              AND t.relname = '#{table_name}'
+              AND i.relnamespace IN (SELECT oid FROM pg_namespace WHERE nspname = ANY (current_schemas(false)) )
+          SQL
+        end
+
         # Returns an array of indexes for the given table.
         def indexes(table_name, name = nil)
            result = query(<<-SQL, 'SCHEMA')
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index a471383041..36c7462419 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -586,11 +586,16 @@ module ActiveRecord
 
       # Is this connection alive and ready for queries?
       def active?
-        @connection.connect_poll != PG::PGRES_POLLING_FAILED
+        @connection.query 'SELECT 1'
+        true
       rescue PGError
         false
       end
 
+      def active_threadsafe?
+        @connection.connect_poll != PG::PGRES_POLLING_FAILED
+      end
+
       # Close then reopen the connection.
       def reconnect!
         super
@@ -942,14 +947,6 @@ module ActiveRecord
           exec_query(sql, name, binds)
         end
 
-        def select_raw(sql, name = nil)
-          res = execute(sql, name)
-          results = result_as_array(res)
-          fields = res.fields
-          res.clear
-          return fields, results
-        end
-
         # Returns the list of a table's column names, data types, and default values.
         #
         # The underlying query is roughly:
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
index 55533311f5..1e299f12cd 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
@@ -347,8 +347,8 @@ module ActiveRecord
       end
       alias :create :insert_sql
 
-      def select_rows(sql, name = nil)
-        exec_query(sql, name).rows
+      def select_rows(sql, name = nil, binds = [])
+        exec_query(sql, name, binds).rows
       end
 
       def begin_db_transaction #:nodoc:
diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index cd8690d500..d9aaf8597f 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -76,6 +76,15 @@ module ActiveRecord
       mattr_accessor :timestamped_migrations, instance_writer: false
       self.timestamped_migrations = true
 
+      ##
+      # :singleton-method:
+      # Specify whether schema dump should happen at the end of the
+      # db:migrate rake task. This is true by default, which is useful for the
+      # development environment. This should ideally be false in the production
+      # environment where dumping schema is rarely needed.
+      mattr_accessor :dump_schema_after_migration, instance_writer: false
+      self.dump_schema_after_migration = true
+
       # :nodoc:
       mattr_accessor :maintain_test_schema, instance_accessor: false
 
@@ -138,12 +147,12 @@ module ActiveRecord
       #   class Post < ActiveRecord::Base
       #     scope :published_and_commented, -> { published.and(self.arel_table[:comments_count].gt(0)) }
       #   end
-      def arel_table
+      def arel_table # :nodoc:
         @arel_table ||= Arel::Table.new(table_name, arel_engine)
       end
 
       # Returns the Arel engine.
-      def arel_engine
+      def arel_engine # :nodoc:
         @arel_engine ||=
           if Base == self || connection_handler.retrieve_connection_pool(self)
             self
@@ -182,9 +191,7 @@ module ActiveRecord
       @column_types = self.class.column_types
 
       init_internals
-      init_changed_attributes
-      ensure_proper_type
-      populate_with_current_scope_attributes
+      initialize_internals_callback
 
       # +options+ argument is only needed to make protected_attributes gem easier to hook.
       # Remove it when we drop support to this gem.
@@ -255,16 +262,12 @@ module ActiveRecord
 
       run_callbacks(:initialize) unless _initialize_callbacks.empty?
 
-      @changed_attributes = {}
-      init_changed_attributes
-
       @aggregation_cache = {}
       @association_cache = {}
       @attributes_cache  = {}
 
       @new_record  = true
 
-      ensure_proper_type
       super
     end
 
@@ -281,7 +284,7 @@ module ActiveRecord
     #   Post.new.encode_with(coder)
     #   coder # => {"attributes" => {"id" => nil, ... }}
     def encode_with(coder)
-      coder['attributes'] = attributes
+      coder['attributes'] = attributes_for_coder
     end
 
     # Returns true if +comparison_object+ is the same exact object, or +comparison_object+
@@ -397,13 +400,10 @@ module ActiveRecord
     end
 
     def update_attributes_from_transaction_state(transaction_state, depth)
-      if transaction_state && !has_transactional_callbacks?
+      if transaction_state && transaction_state.finalized? && !has_transactional_callbacks?
         unless @reflects_state[depth]
-          if transaction_state.committed?
-            committed!
-          elsif transaction_state.rolledback?
-            rolledback!
-          end
+          restore_transaction_record_state if transaction_state.rolledback?
+          clear_transaction_record_state
           @reflects_state[depth] = true
         end
 
@@ -443,13 +443,7 @@ module ActiveRecord
       @reflects_state           = [false]
     end
 
-    def init_changed_attributes
-      # Intentionally avoid using #column_defaults since overridden defaults (as is done in
-      # optimistic locking) won't get written unless they get marked as changed
-      self.class.columns.each do |c|
-        attr, orig_value = c.name, c.default
-        changed_attributes[attr] = orig_value if _field_changed?(attr, orig_value, @attributes[attr])
-      end
+    def initialize_internals_callback
     end
 
     # This method is needed to make protected_attributes gem easier to hook.
diff --git a/activerecord/lib/active_record/dynamic_matchers.rb b/activerecord/lib/active_record/dynamic_matchers.rb
index 5caab09038..e94b74063e 100644
--- a/activerecord/lib/active_record/dynamic_matchers.rb
+++ b/activerecord/lib/active_record/dynamic_matchers.rb
@@ -6,8 +6,12 @@ module ActiveRecord
     # then we can remove the indirection.
 
     def respond_to?(name, include_private = false)
-      match = Method.match(self, name)
-      match && match.valid? || super
+      if self == Base
+        super
+      else
+        match = Method.match(self, name)
+        match && match.valid? || super
+      end
     end
 
     private
diff --git a/activerecord/lib/active_record/enum.rb b/activerecord/lib/active_record/enum.rb
index 3deb2d65f8..4aa323fb00 100644
--- a/activerecord/lib/active_record/enum.rb
+++ b/activerecord/lib/active_record/enum.rb
@@ -62,7 +62,15 @@ module ActiveRecord
   # Use that class method when you need to know the ordinal value of an enum:
   #
   #   Conversation.where("status <> ?", Conversation.statuses[:archived])
+  #
+  # Where conditions on an enum attribute must use the ordinal value of an enum.
   module Enum
+    DEFINED_ENUMS = {} # :nodoc:
+
+    def enum_mapping_for(attr_name) # :nodoc:
+      DEFINED_ENUMS[attr_name.to_s]
+    end
+
     def enum(definitions)
       klass = self
       definitions.each do |name, values|
@@ -71,10 +79,12 @@ module ActiveRecord
         name        = name.to_sym
 
         # def self.statuses statuses end
+        detect_enum_conflict!(name, name.to_s.pluralize, true)
         klass.singleton_class.send(:define_method, name.to_s.pluralize) { enum_values }
 
         _enum_methods_module.module_eval do
           # def status=(value) self[:status] = statuses[value] end
+          klass.send(:detect_enum_conflict!, name, "#{name}=")
           define_method("#{name}=") { |value|
             if enum_values.has_key?(value) || value.blank?
               self[name] = enum_values[value]
@@ -89,24 +99,31 @@ module ActiveRecord
           }
 
           # def status() statuses.key self[:status] end
+          klass.send(:detect_enum_conflict!, name, name)
           define_method(name) { enum_values.key self[name] }
 
           # def status_before_type_cast() statuses.key self[:status] end
+          klass.send(:detect_enum_conflict!, name, "#{name}_before_type_cast")
           define_method("#{name}_before_type_cast") { enum_values.key self[name] }
 
           pairs = values.respond_to?(:each_pair) ? values.each_pair : values.each_with_index
           pairs.each do |value, i|
             enum_values[value] = i
 
-            # scope :active, -> { where status: 0 }
-            klass.scope value, -> { klass.where name => i }
-
             # def active?() status == 0 end
+            klass.send(:detect_enum_conflict!, name, "#{value}?")
             define_method("#{value}?") { self[name] == i }
 
             # def active!() update! status: :active end
+            klass.send(:detect_enum_conflict!, name, "#{value}!")
             define_method("#{value}!") { update! name => value }
+
+            # scope :active, -> { where status: 0 }
+            klass.send(:detect_enum_conflict!, name, value, true)
+            klass.scope value, -> { klass.where name => i }
           end
+
+          DEFINED_ENUMS[name.to_s] = enum_values
         end
       end
     end
@@ -114,10 +131,64 @@ module ActiveRecord
     private
       def _enum_methods_module
         @_enum_methods_module ||= begin
-          mod = Module.new
+          mod = Module.new do
+            private
+              def save_changed_attribute(attr_name, value)
+                if (mapping = self.class.enum_mapping_for(attr_name))
+                  if attribute_changed?(attr_name)
+                    old = changed_attributes[attr_name]
+
+                    if mapping[old] == value
+                      changed_attributes.delete(attr_name)
+                    end
+                  else
+                    old = clone_attribute_value(:read_attribute, attr_name)
+
+                    if old != value
+                      changed_attributes[attr_name] = mapping.key old
+                    end
+                  end
+                else
+                  super
+                end
+              end
+          end
           include mod
           mod
         end
       end
+
+      ENUM_CONFLICT_MESSAGE = \
+        "You tried to define an enum named \"%{enum}\" on the model \"%{klass}\", but " \
+        "this will generate a %{type} method \"%{method}\", which is already defined " \
+        "by %{source}."
+
+      def detect_enum_conflict!(enum_name, method_name, klass_method = false)
+        if klass_method && dangerous_class_method?(method_name)
+          raise ArgumentError, ENUM_CONFLICT_MESSAGE % {
+            enum: enum_name,
+            klass: self.name,
+            type: 'class',
+            method: method_name,
+            source: 'Active Record'
+          }
+        elsif !klass_method && dangerous_attribute_method?(method_name)
+          raise ArgumentError, ENUM_CONFLICT_MESSAGE % {
+            enum: enum_name,
+            klass: self.name,
+            type: 'instance',
+            method: method_name,
+            source: 'Active Record'
+          }
+        elsif !klass_method && method_defined_within?(method_name, _enum_methods_module, Module)
+          raise ArgumentError, ENUM_CONFLICT_MESSAGE % {
+            enum: enum_name,
+            klass: self.name,
+            type: 'instance',
+            method: method_name,
+            source: 'another enum'
+          }
+        end
+      end
   end
 end
diff --git a/activerecord/lib/active_record/inheritance.rb b/activerecord/lib/active_record/inheritance.rb
index da73112e90..08fc91c9df 100644
--- a/activerecord/lib/active_record/inheritance.rb
+++ b/activerecord/lib/active_record/inheritance.rb
@@ -195,8 +195,18 @@ module ActiveRecord
       end
     end
 
+    def initialize_dup(other)
+      super
+      ensure_proper_type
+    end
+
     private
 
+    def initialize_internals_callback
+      super
+      ensure_proper_type
+    end
+
     # Sets the attribute used for single table inheritance to this class name if this is not the
     # ActiveRecord::Base descendant.
     # Considering the hierarchy Reply < Message < ActiveRecord::Base, this makes it possible to
diff --git a/activerecord/lib/active_record/migration.rb b/activerecord/lib/active_record/migration.rb
index b57da73969..b6b02322d7 100644
--- a/activerecord/lib/active_record/migration.rb
+++ b/activerecord/lib/active_record/migration.rb
@@ -385,8 +385,8 @@ module ActiveRecord
       attr_accessor :delegate # :nodoc:
       attr_accessor :disable_ddl_transaction # :nodoc:
 
-      def check_pending!
-        raise ActiveRecord::PendingMigrationError if ActiveRecord::Migrator.needs_migration?
+      def check_pending!(connection = Base.connection)
+        raise ActiveRecord::PendingMigrationError if ActiveRecord::Migrator.needs_migration?(connection)
       end
 
       def load_schema_if_pending!
@@ -830,17 +830,17 @@ module ActiveRecord
         SchemaMigration.all.map { |x| x.version.to_i }.sort
       end
 
-      def current_version
+      def current_version(connection = Base.connection)
         sm_table = schema_migrations_table_name
-        if Base.connection.table_exists?(sm_table)
+        if connection.table_exists?(sm_table)
           get_all_versions.max || 0
         else
           0
         end
       end
 
-      def needs_migration?
-        current_version < last_version
+      def needs_migration?(connection = Base.connection)
+        current_version(connection) < last_version
       end
 
       def last_version
diff --git a/activerecord/lib/active_record/migration/command_recorder.rb b/activerecord/lib/active_record/migration/command_recorder.rb
index 9139ad953c..c44d8c1665 100644
--- a/activerecord/lib/active_record/migration/command_recorder.rb
+++ b/activerecord/lib/active_record/migration/command_recorder.rb
@@ -140,7 +140,12 @@ module ActiveRecord
 
       def invert_add_index(args)
         table, columns, options = *args
-        [:remove_index, [table, (options || {}).merge(column: columns)]]
+        options ||= {}
+
+        index_name = options[:name]
+        options_hash = index_name ? { name: index_name } : { column: columns }
+
+        [:remove_index, [table, options_hash]]
       end
 
       def invert_remove_index(args)
diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index 460fbdb3f8..b1b35ed940 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -389,7 +389,7 @@ module ActiveRecord
 
       fresh_object =
         if options && options[:lock]
-          self.class.unscoped { self.class.lock.find(id) }
+          self.class.unscoped { self.class.lock(options[:lock]).find(id) }
         else
           self.class.unscoped { self.class.find(id) }
         end
diff --git a/activerecord/lib/active_record/querying.rb b/activerecord/lib/active_record/querying.rb
index fd4c973504..ef138c6f80 100644
--- a/activerecord/lib/active_record/querying.rb
+++ b/activerecord/lib/active_record/querying.rb
@@ -1,6 +1,7 @@
 module ActiveRecord
   module Querying
     delegate :find, :take, :take!, :first, :first!, :last, :last!, :exists?, :any?, :many?, to: :all
+    delegate :second, :second!, :third, :third!, :fourth, :fourth!, :fifth, :fifth!, :forty_two, :forty_two!, to: :all
     delegate :first_or_create, :first_or_create!, :first_or_initialize, to: :all
     delegate :find_or_create_by, :find_or_create_by!, :find_or_initialize_by, to: :all
     delegate :find_by, :find_by!, to: :all
diff --git a/activerecord/lib/active_record/railties/databases.rake b/activerecord/lib/active_record/railties/databases.rake
index 561387a179..1d5c80bc01 100644
--- a/activerecord/lib/active_record/railties/databases.rake
+++ b/activerecord/lib/active_record/railties/databases.rake
@@ -34,7 +34,7 @@ db_namespace = namespace :db do
     ActiveRecord::Migrator.migrate(ActiveRecord::Migrator.migrations_paths, ENV["VERSION"] ? ENV["VERSION"].to_i : nil) do |migration|
       ENV["SCOPE"].blank? || (ENV["SCOPE"] == migration.scope)
     end
-    db_namespace['_dump'].invoke
+    db_namespace['_dump'].invoke if ActiveRecord::Base.dump_schema_after_migration
   end
 
   task :_dump do
@@ -75,7 +75,7 @@ db_namespace = namespace :db do
     # desc 'Runs the "down" for a given migration VERSION.'
     task :down => [:environment, :load_config] do
       version = ENV['VERSION'] ? ENV['VERSION'].to_i : nil
-      raise 'VERSION is required' unless version
+      raise 'VERSION is required - To go down one migration, run db:rollback' unless version
       ActiveRecord::Migrator.run(:down, ActiveRecord::Migrator.migrations_paths, version)
       db_namespace['_dump'].invoke
     end
diff --git a/activerecord/lib/active_record/relation.rb b/activerecord/lib/active_record/relation.rb
index 770b48c550..0959860ec6 100644
--- a/activerecord/lib/active_record/relation.rb
+++ b/activerecord/lib/active_record/relation.rb
@@ -24,6 +24,7 @@ module ActiveRecord
       @klass  = klass
       @table  = table
       @values = values
+      @offsets = {}
       @loaded = false
     end
 
@@ -496,9 +497,10 @@ module ActiveRecord
     end
 
     def reset
-      @first = @last = @to_sql = @order_clause = @scope_for_create = @arel = @loaded = nil
+      @last = @to_sql = @order_clause = @scope_for_create = @arel = @loaded = nil
       @should_eager_load = @join_dependency = nil
       @records = []
+      @offsets = {}
       self
     end
 
@@ -534,7 +536,6 @@ module ActiveRecord
       }
 
       binds = Hash[bind_values.find_all(&:first).map { |column, v| [column.name, v] }]
-      binds.merge!(Hash[bind_values.find_all(&:first).map { |column, v| [column.name, v] }])
 
       Hash[equalities.map { |where|
         name = where.left.name
diff --git a/activerecord/lib/active_record/relation/batches.rb b/activerecord/lib/active_record/relation/batches.rb
index 49b01909c6..29fc150b3d 100644
--- a/activerecord/lib/active_record/relation/batches.rb
+++ b/activerecord/lib/active_record/relation/batches.rb
@@ -52,7 +52,9 @@ module ActiveRecord
           records.each { |record| yield record }
         end
       else
-        enum_for :find_each, options
+        enum_for :find_each, options do
+          options[:start] ? where(table[primary_key].gteq(options[:start])).size : size
+        end
       end
     end
 
@@ -64,6 +66,16 @@ module ActiveRecord
     #     group.each { |person| person.party_all_night! }
     #   end
     #
+    # If you do not provide a block to #find_in_batches, it will return an Enumerator
+    # for chaining with other methods:
+    #
+    #   Person.find_in_batches.with_index do |group, batch|
+    #     puts "Processing group ##{batch}"
+    #     group.each(&:recover_from_last_night!)
+    #   end
+    #
+    # To be yielded each record one by one, use #find_each instead.
+    #
     # ==== Options
     # * <tt>:batch_size</tt> - Specifies the size of the batch. Default to 1000.
     # * <tt>:start</tt> - Specifies the starting point for the batch processing.
@@ -88,30 +100,33 @@ module ActiveRecord
       options.assert_valid_keys(:start, :batch_size)
 
       relation = self
+      start = options[:start]
+      batch_size = options[:batch_size] || 1000
+
+      unless block_given?
+        return to_enum(:find_in_batches, options) do
+          total = start ? where(table[primary_key].gteq(start)).size : size
+          (total - 1).div(batch_size) + 1
+        end
+      end
 
       if logger && (arel.orders.present? || arel.taken.present?)
         logger.warn("Scoped order and limit are ignored, it's forced to be batch order and batch size")
       end
 
-      start = options.delete(:start)
-      batch_size = options.delete(:batch_size) || 1000
-
       relation = relation.reorder(batch_order).limit(batch_size)
       records = start ? relation.where(table[primary_key].gteq(start)).to_a : relation.to_a
 
       while records.any?
         records_size = records.size
         primary_key_offset = records.last.id
+        raise "Primary key not included in the custom select clause" unless primary_key_offset
 
         yield records
 
         break if records_size < batch_size
 
-        if primary_key_offset
-          records = relation.where(table[primary_key].gt(primary_key_offset)).to_a
-        else
-          raise "Primary key not included in the custom select clause"
-        end
+        records = relation.where(table[primary_key].gt(primary_key_offset)).to_a
       end
     end
 
diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index 64ac265689..4519a756a7 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -127,9 +127,9 @@ module ActiveRecord
     #
     def first(limit = nil)
       if limit
-        find_first_with_limit(limit)
+        find_nth_with_limit(offset_value, limit)
       else
-        find_first
+        find_nth(:first, offset_value)
       end
     end
 
@@ -172,6 +172,86 @@ module ActiveRecord
       last or raise RecordNotFound
     end
 
+    # Find the second record.
+    # If no order is defined it will order by primary key.
+    #
+    #   Person.second # returns the second object fetched by SELECT * FROM people
+    #   Person.offset(3).second # returns the second object from OFFSET 3 (which is OFFSET 4)
+    #   Person.where(["user_name = :u", { u: user_name }]).second
+    def second
+      find_nth(:second, offset_value ? offset_value + 1 : 1)
+    end
+
+    # Same as +second+ but raises <tt>ActiveRecord::RecordNotFound</tt> if no record
+    # is found.
+    def second!
+      second or raise RecordNotFound
+    end
+
+    # Find the third record.
+    # If no order is defined it will order by primary key.
+    #
+    #   Person.third # returns the third object fetched by SELECT * FROM people
+    #   Person.offset(3).third # returns the third object from OFFSET 3 (which is OFFSET 5)
+    #   Person.where(["user_name = :u", { u: user_name }]).third
+    def third
+      find_nth(:third, offset_value ? offset_value + 2 : 2)
+    end
+
+    # Same as +third+ but raises <tt>ActiveRecord::RecordNotFound</tt> if no record
+    # is found.
+    def third!
+      third or raise RecordNotFound
+    end
+
+    # Find the fourth record.
+    # If no order is defined it will order by primary key.
+    #
+    #   Person.fourth # returns the fourth object fetched by SELECT * FROM people
+    #   Person.offset(3).fourth # returns the fourth object from OFFSET 3 (which is OFFSET 6)
+    #   Person.where(["user_name = :u", { u: user_name }]).fourth
+    def fourth
+      find_nth(:fourth, offset_value ? offset_value + 3 : 3)
+    end
+
+    # Same as +fourth+ but raises <tt>ActiveRecord::RecordNotFound</tt> if no record
+    # is found.
+    def fourth!
+      fourth or raise RecordNotFound
+    end
+
+    # Find the fifth record.
+    # If no order is defined it will order by primary key.
+    #
+    #   Person.fifth # returns the fifth object fetched by SELECT * FROM people
+    #   Person.offset(3).fifth # returns the fifth object from OFFSET 3 (which is OFFSET 7)
+    #   Person.where(["user_name = :u", { u: user_name }]).fifth
+    def fifth
+      find_nth(:fifth, offset_value ? offset_value + 4 : 4)
+    end
+
+    # Same as +fifth+ but raises <tt>ActiveRecord::RecordNotFound</tt> if no record
+    # is found.
+    def fifth!
+      fifth or raise RecordNotFound
+    end
+
+    # Find the forty-second record. Also known as accessing "the reddit".
+    # If no order is defined it will order by primary key.
+    #
+    #   Person.forty_two # returns the forty-second object fetched by SELECT * FROM people
+    #   Person.offset(3).forty_two # returns the fifth object from OFFSET 3 (which is OFFSET 44)
+    #   Person.where(["user_name = :u", { u: user_name }]).forty_two
+    def forty_two
+      find_nth(:forty_two, offset_value ? offset_value + 41 : 41)
+    end
+
+    # Same as +forty_two+ but raises <tt>ActiveRecord::RecordNotFound</tt> if no record
+    # is found.
+    def forty_two!
+      forty_two or raise RecordNotFound
+    end
+
     # Returns +true+ if a record exists in the table that matches the +id+ or
     # conditions given, or +false+ otherwise. The argument can take six forms:
     #
@@ -231,9 +311,9 @@ module ActiveRecord
       conditions = " [#{conditions}]" if conditions
 
       if Array(ids).size == 1
-        error = "Couldn't find #{@klass.name} with #{primary_key}=#{ids}#{conditions}"
+        error = "Couldn't find #{@klass.name} with '#{primary_key}'=#{ids}#{conditions}"
       else
-        error = "Couldn't find all #{@klass.name.pluralize} with IDs "
+        error = "Couldn't find all #{@klass.name.pluralize} with '#{primary_key}': "
         error << "(#{ids.join(", ")})#{conditions} (found #{result_size} results, but was looking for #{expected_size})"
       end
 
@@ -268,7 +348,15 @@ module ActiveRecord
     end
 
     def construct_relation_for_association_calculations
-      apply_join_dependency(self, construct_join_dependency(arel.froms.first))
+      from = arel.froms.first
+      if Arel::Table === from
+        apply_join_dependency(self, construct_join_dependency)
+      else
+        # FIXME: as far as I can tell, `from` will always be an Arel::Table.
+        # There are no tests that test this branch, but presumably it's
+        # possible for `from` to be a list?
+        apply_join_dependency(self, construct_join_dependency(from))
+      end
     end
 
     def apply_join_dependency(relation, join_dependency)
@@ -365,19 +453,19 @@ module ActiveRecord
       end
     end
 
-    def find_first
+    def find_nth(ordinal, offset)
       if loaded?
-        @records.first
+        @records.send(ordinal)
       else
-        @first ||= find_first_with_limit(1).first
+        @offsets[offset] ||= find_nth_with_limit(offset, 1).first
       end
     end
 
-    def find_first_with_limit(limit)
+    def find_nth_with_limit(offset, limit)
       if order_values.empty? && primary_key
-        order(arel_table[primary_key].asc).limit(limit).to_a
+        order(arel_table[primary_key].asc).limit(limit).offset(offset).to_a
       else
-        limit(limit).to_a
+        limit(limit).offset(offset).to_a
       end
     end
 
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index 6cf57b679d..7d2b427289 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -120,6 +120,9 @@ module ActiveRecord
     # Will throw an error, but this will work:
     #
     #   User.includes(:posts).where('posts.name = ?', 'example').references(:posts)
+    #
+    # Note that +includes+ works with association names while +references+ needs
+    # the actual table name.
     def includes(*args)
       check_if_method_has_arguments!(:includes, args)
       spawn.includes!(*args)
@@ -163,24 +166,26 @@ module ActiveRecord
       self
     end
 
-    # Used to indicate that an association is referenced by an SQL string, and should
-    # therefore be JOINed in any query rather than loaded separately.
+    # Use to indicate that the given +table_names+ are referenced by an SQL string,
+    # and should therefore be JOINed in any query rather than loaded separately.
+    # This method only works in conjuction with +includes+.
+    # See #includes for more details.
     #
     #   User.includes(:posts).where("posts.name = 'foo'")
     #   # => Doesn't JOIN the posts table, resulting in an error.
     #
     #   User.includes(:posts).where("posts.name = 'foo'").references(:posts)
     #   # => Query now knows the string references posts, so adds a JOIN
-    def references(*args)
-      check_if_method_has_arguments!(:references, args)
-      spawn.references!(*args)
+    def references(*table_names)
+      check_if_method_has_arguments!(:references, table_names)
+      spawn.references!(*table_names)
     end
 
-    def references!(*args) # :nodoc:
-      args.flatten!
-      args.map!(&:to_s)
+    def references!(*table_names) # :nodoc:
+      table_names.flatten!
+      table_names.map!(&:to_s)
 
-      self.references_values |= args
+      self.references_values |= table_names
       self
     end
 
@@ -234,7 +239,9 @@ module ActiveRecord
 
     def select!(*fields) # :nodoc:
       fields.flatten!
-
+      fields.map! do |field|
+        klass.attribute_alias?(field) ? klass.attribute_alias(field).to_sym : field
+      end
       self.select_values += fields
       self
     end
@@ -817,11 +824,12 @@ module ActiveRecord
     end
 
     # Returns the Arel object associated with the relation.
-    def arel
+    def arel # :nodoc:
       @arel ||= build_arel
     end
 
-    # Like #arel, but ignores the default scope of the model.
+    private
+
     def build_arel
       arel = Arel::SelectManager.new(table.engine, table)
 
@@ -856,8 +864,6 @@ module ActiveRecord
       arel
     end
 
-    private
-
     def symbol_unscoping(scope)
       if !VALID_UNSCOPING_VALUES.include?(scope)
         raise ArgumentError, "Called unscope() with invalid unscoping argument ':#{scope}'. Valid arguments are :#{VALID_UNSCOPING_VALUES.to_a.join(", :")}."
@@ -887,8 +893,6 @@ module ActiveRecord
         when Arel::Nodes::In, Arel::Nodes::NotIn, Arel::Nodes::Equality, Arel::Nodes::NotEqual
           subrelation = (rel.left.kind_of?(Arel::Attributes::Attribute) ? rel.left : rel.right)
           subrelation.name == target_value
-        else
-          raise "unscope(where: #{target_value.inspect}) failed: unscoping #{rel.class} is unimplemented."
         end
       end
 
@@ -1022,7 +1026,10 @@ module ActiveRecord
 
     def build_select(arel, selects)
       if !selects.empty?
-        arel.project(*selects)
+        expanded_select = selects.map do |field|
+          columns_hash.key?(field.to_s) ? arel_table[field] : field
+        end
+        arel.project(*expanded_select)
       elsif from_value
         arel.project(Arel.star)
       else
@@ -1080,9 +1087,11 @@ module ActiveRecord
       order_args.map! do |arg|
         case arg
         when Symbol
+          arg = klass.attribute_alias(arg).to_sym if klass.attribute_alias?(arg)
           table[arg].asc
         when Hash
           arg.map { |field, dir|
+            field = klass.attribute_alias(field).to_sym if klass.attribute_alias?(field)
             table[field].send(dir)
           }
         else
diff --git a/activerecord/lib/active_record/result.rb b/activerecord/lib/active_record/result.rb
index 469451e2f4..228b2aa60f 100644
--- a/activerecord/lib/active_record/result.rb
+++ b/activerecord/lib/active_record/result.rb
@@ -54,7 +54,7 @@ module ActiveRecord
       if block_given?
         hash_rows.each { |row| yield row }
       else
-        hash_rows.to_enum
+        hash_rows.to_enum { @rows.size }
       end
     end
 
diff --git a/activerecord/lib/active_record/sanitization.rb b/activerecord/lib/active_record/sanitization.rb
index dacaec26b7..5a71c13d91 100644
--- a/activerecord/lib/active_record/sanitization.rb
+++ b/activerecord/lib/active_record/sanitization.rb
@@ -29,6 +29,7 @@ module ActiveRecord
         end
       end
       alias_method :sanitize_sql, :sanitize_sql_for_conditions
+      alias_method :sanitize_conditions, :sanitize_sql
 
       # Accepts an array, hash, or string of SQL conditions and sanitizes
       # them into a valid SQL fragment for a SET clause.
@@ -122,8 +123,6 @@ module ActiveRecord
         end
       end
 
-      alias_method :sanitize_conditions, :sanitize_sql
-
       def replace_bind_variables(statement, values) #:nodoc:
         raise_if_bind_arity_mismatch(statement, statement.count('?'), values.size)
         bound = values.dup
diff --git a/activerecord/lib/active_record/scoping.rb b/activerecord/lib/active_record/scoping.rb
index 0cf3d59985..3e43591672 100644
--- a/activerecord/lib/active_record/scoping.rb
+++ b/activerecord/lib/active_record/scoping.rb
@@ -27,6 +27,11 @@ module ActiveRecord
       end
     end
 
+    def initialize_internals_callback
+      super
+      populate_with_current_scope_attributes
+    end
+
     # This class stores the +:current_scope+ and +:ignore_default_scope+ values
     # for different classes. The registry is stored as a thread local, which is
     # accessed through +ScopeRegistry.current+.
diff --git a/activerecord/lib/active_record/scoping/named.rb b/activerecord/lib/active_record/scoping/named.rb
index 2a5718f388..49cadb66d0 100644
--- a/activerecord/lib/active_record/scoping/named.rb
+++ b/activerecord/lib/active_record/scoping/named.rb
@@ -139,6 +139,12 @@ module ActiveRecord
         #   Article.published.featured.latest_article
         #   Article.featured.titles
         def scope(name, body, &block)
+          if dangerous_class_method?(name)
+            raise ArgumentError, "You tried to define a scope named \"#{name}\" " \
+              "on the model \"#{self.name}\", but Active Record already defined " \
+              "a class method with the same name."
+          end
+
           extension = Module.new(&block) if block
 
           singleton_class.send(:define_method, name) do |*args|
diff --git a/activerecord/lib/active_record/timestamp.rb b/activerecord/lib/active_record/timestamp.rb
index e0541b7681..7178bed560 100644
--- a/activerecord/lib/active_record/timestamp.rb
+++ b/activerecord/lib/active_record/timestamp.rb
@@ -37,8 +37,8 @@ module ActiveRecord
     end
 
     def initialize_dup(other) # :nodoc:
-      clear_timestamp_attributes
       super
+      clear_timestamp_attributes
     end
 
   private
@@ -71,7 +71,7 @@ module ActiveRecord
     end
 
     def should_record_timestamps?
-      self.record_timestamps && (!partial_writes? || changed? || (attributes.keys & self.class.serialized_attributes.keys).present?)
+      self.record_timestamps && (!partial_writes? || changed?)
     end
 
     def timestamp_attributes_for_create_in_model
diff --git a/activerecord/lib/active_record/transactions.rb b/activerecord/lib/active_record/transactions.rb
index c33ffeece0..ec3e8f281b 100644
--- a/activerecord/lib/active_record/transactions.rb
+++ b/activerecord/lib/active_record/transactions.rb
@@ -295,7 +295,7 @@ module ActiveRecord
     def committed! #:nodoc:
       run_callbacks :commit if destroyed? || persisted?
     ensure
-      clear_transaction_record_state
+      @_start_transaction_state.clear
     end
 
     # Call the +after_rollback+ callbacks. The +force_restore_state+ argument indicates if the record