Merge branch 'master' into feature/reselect-method

27 files changed, 861 insertions, 622 deletions

diff --git a/activerecord/lib/active_record/association_relation.rb b/activerecord/lib/active_record/association_relation.rb
index 403667fb70..4c538ef2bd 100644
--- a/activerecord/lib/active_record/association_relation.rb
+++ b/activerecord/lib/active_record/association_relation.rb
@@ -31,9 +31,9 @@ module ActiveRecord
     private
 
       def exec_queries
-        super do |r|
-          @association.set_inverse_instance r
-          yield r if block_given?
+        super do |record|
+          @association.set_inverse_instance_from_queries(record)
+          yield record if block_given?
         end
       end
   end
diff --git a/activerecord/lib/active_record/associations/association.rb b/activerecord/lib/active_record/associations/association.rb
index 44596f4424..bf4942aac8 100644
--- a/activerecord/lib/active_record/associations/association.rb
+++ b/activerecord/lib/active_record/associations/association.rb
@@ -40,7 +40,9 @@ module ActiveRecord
       end
 
       # Reloads the \target and returns +self+ on success.
-      def reload
+      # The QueryCache is cleared if +force+ is true.
+      def reload(force = false)
+        klass.connection.clear_query_cache if force && klass
         reset
         reset_scope
         load_target
@@ -79,18 +81,6 @@ module ActiveRecord
         target_scope.merge!(association_scope)
       end
 
-      # The scope for this association.
-      #
-      # Note that the association_scope is merged into the target_scope only when the
-      # scope method is called. This is because at that point the call may be surrounded
-      # by scope.scoping { ... } or with_scope { ... } etc, which affects the scope which
-      # actually gets built.
-      def association_scope
-        if klass
-          @association_scope ||= AssociationScope.scope(self)
-        end
-      end
-
       def reset_scope
         @association_scope = nil
       end
@@ -103,6 +93,13 @@ module ActiveRecord
         record
       end
 
+      def set_inverse_instance_from_queries(record)
+        if inverse = inverse_association_for(record)
+          inverse.inversed_from_queries(owner)
+        end
+        record
+      end
+
       # Remove the inverse association, if possible
       def remove_inverse_instance(record)
         if inverse = inverse_association_for(record)
@@ -114,6 +111,7 @@ module ActiveRecord
         self.target = record
         @inversed = !!record
       end
+      alias :inversed_from_queries :inversed_from
 
       # Returns the class of the target. belongs_to polymorphic overrides this to look at the
       # polymorphic_type field on the owner.
@@ -121,12 +119,6 @@ module ActiveRecord
         reflection.klass
       end
 
-      # Can be overridden (i.e. in ThroughAssociation) to merge in other scopes (i.e. the
-      # through association's scope)
-      def target_scope
-        AssociationRelation.create(klass, self).merge!(klass.all)
-      end
-
       def extensions
         extensions = klass.default_extensions | reflection.extensions
 
@@ -187,6 +179,24 @@ module ActiveRecord
       end
 
       private
+        # The scope for this association.
+        #
+        # Note that the association_scope is merged into the target_scope only when the
+        # scope method is called. This is because at that point the call may be surrounded
+        # by scope.scoping { ... } or unscoped { ... } etc, which affects the scope which
+        # actually gets built.
+        def association_scope
+          if klass
+            @association_scope ||= AssociationScope.scope(self)
+          end
+        end
+
+        # Can be overridden (i.e. in ThroughAssociation) to merge in other scopes (i.e. the
+        # through association's scope)
+        def target_scope
+          AssociationRelation.create(klass, self).merge!(klass.all)
+        end
+
         def scope_for_create
           scope.scope_for_create
         end
diff --git a/activerecord/lib/active_record/associations/builder/collection_association.rb b/activerecord/lib/active_record/associations/builder/collection_association.rb
index 35a72c3850..ff57c40121 100644
--- a/activerecord/lib/active_record/associations/builder/collection_association.rb
+++ b/activerecord/lib/active_record/associations/builder/collection_association.rb
@@ -24,7 +24,7 @@ module ActiveRecord::Associations::Builder # :nodoc:
       if block_given?
         extension_module_name = "#{model.name.demodulize}#{name.to_s.camelize}AssociationExtension"
         extension = Module.new(&Proc.new)
-        model.parent.const_set(extension_module_name, extension)
+        model.module_parent.const_set(extension_module_name, extension)
       end
     end
 
diff --git a/activerecord/lib/active_record/associations/collection_proxy.rb b/activerecord/lib/active_record/associations/collection_proxy.rb
index 9a30198b95..08b7c9274d 100644
--- a/activerecord/lib/active_record/associations/collection_proxy.rb
+++ b/activerecord/lib/active_record/associations/collection_proxy.rb
@@ -1088,7 +1088,7 @@ module ActiveRecord
       #   person.pets.reload # fetches pets from the database
       #   # => [#<Pet id: 1, name: "Snoop", group: "dogs", person_id: 1>]
       def reload
-        proxy_association.reload
+        proxy_association.reload(true)
         reset_scope
       end
 
diff --git a/activerecord/lib/active_record/associations/has_many_through_association.rb b/activerecord/lib/active_record/associations/has_many_through_association.rb
index 617956c768..f84ac65fa2 100644
--- a/activerecord/lib/active_record/associations/has_many_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -21,20 +21,6 @@ module ActiveRecord
         super
       end
 
-      def concat_records(records)
-        ensure_not_nested
-
-        records = super(records, true)
-
-        if owner.new_record? && records
-          records.flatten.each do |record|
-            build_through_record(record)
-          end
-        end
-
-        records
-      end
-
       def insert_record(record, validate = true, raise = false)
         ensure_not_nested
 
@@ -48,6 +34,20 @@ module ActiveRecord
       end
 
       private
+        def concat_records(records)
+          ensure_not_nested
+
+          records = super(records, true)
+
+          if owner.new_record? && records
+            records.flatten.each do |record|
+              build_through_record(record)
+            end
+          end
+
+          records
+        end
+
         # The through record (built with build_record) is temporarily cached
         # so that it may be reused if insert_record is subsequently called.
         #
diff --git a/activerecord/lib/active_record/associations/preloader.rb b/activerecord/lib/active_record/associations/preloader.rb
index a8f94b574d..8997579527 100644
--- a/activerecord/lib/active_record/associations/preloader.rb
+++ b/activerecord/lib/active_record/associations/preloader.rb
@@ -98,12 +98,11 @@ module ActiveRecord
 
         # Loads all the given data into +records+ for the +association+.
         def preloaders_on(association, records, scope, polymorphic_parent = false)
-          if association.respond_to?(:to_hash)
+          case association
+          when Hash
             preloaders_for_hash(association, records, scope, polymorphic_parent)
-          elsif association.is_a?(Symbol)
+          when Symbol, String
             preloaders_for_one(association, records, scope, polymorphic_parent)
-          elsif association.respond_to?(:to_str)
-            preloaders_for_one(association.to_sym, records, scope, polymorphic_parent)
           else
             raise ArgumentError, "#{association.inspect} was not recognized for preload"
           end
@@ -111,23 +110,21 @@ module ActiveRecord
 
         def preloaders_for_hash(association, records, scope, polymorphic_parent)
           association.flat_map { |parent, child|
-            loaders = preloaders_for_one parent, records, scope, polymorphic_parent
-
-            recs = loaders.flat_map(&:preloaded_records).uniq
-
-            reflection = records.first.class._reflect_on_association(parent)
-            polymorphic_parent = reflection && reflection.options[:polymorphic]
-
-            loaders.concat Array.wrap(child).flat_map { |assoc|
-              preloaders_on assoc, recs, scope, polymorphic_parent
-            }
-            loaders
+            grouped_records(parent, records, polymorphic_parent).flat_map do |reflection, reflection_records|
+              loaders = preloaders_for_reflection(reflection, reflection_records, scope)
+              recs = loaders.flat_map(&:preloaded_records)
+              child_polymorphic_parent = reflection && reflection.options[:polymorphic]
+              loaders.concat Array.wrap(child).flat_map { |assoc|
+                preloaders_on assoc, recs, scope, child_polymorphic_parent
+              }
+              loaders
+            end
           }
         end
 
         # Loads all the given data into +records+ for a singular +association+.
         #
-        # Functions by instantiating a preloader class such as Preloader::HasManyThrough and
+        # Functions by instantiating a preloader class such as Preloader::Association and
         # call the +run+ method for each passed in class in the +records+ argument.
         #
         # Not all records have the same class, so group then preload group on the reflection
@@ -138,12 +135,17 @@ module ActiveRecord
         # classes, depending on the polymorphic_type field. So we group by the classes as
         # well.
         def preloaders_for_one(association, records, scope, polymorphic_parent)
-          grouped_records(association, records, polymorphic_parent).flat_map do |reflection, klasses|
-            klasses.map do |rhs_klass, rs|
-              loader = preloader_for(reflection, rs).new(rhs_klass, rs, reflection, scope)
-              loader.run self
-              loader
+          grouped_records(association, records, polymorphic_parent)
+            .flat_map do |reflection, reflection_records|
+              preloaders_for_reflection reflection, reflection_records, scope
             end
+        end
+
+        def preloaders_for_reflection(reflection, records, scope)
+          records.group_by { |record| record.association(reflection.name).klass }.map do |rhs_klass, rs|
+            loader = preloader_for(reflection, rs).new(rhs_klass, rs, reflection, scope)
+            loader.run self
+            loader
           end
         end
 
@@ -151,11 +153,9 @@ module ActiveRecord
           h = {}
           records.each do |record|
             next unless record
-            next if polymorphic_parent && !record.class._reflect_on_association(association)
-            assoc = record.association(association)
-            next unless assoc.klass
-            klasses = h[assoc.reflection] ||= {}
-            (klasses[assoc.klass] ||= []) << record
+            reflection = record.class._reflect_on_association(association)
+            next if polymorphic_parent && !reflection || !record.association(association).klass
+            (h[reflection] ||= []) << record
           end
           h
         end
diff --git a/activerecord/lib/active_record/associations/singular_association.rb b/activerecord/lib/active_record/associations/singular_association.rb
index cfab16a745..8e50cce102 100644
--- a/activerecord/lib/active_record/associations/singular_association.rb
+++ b/activerecord/lib/active_record/associations/singular_association.rb
@@ -26,7 +26,7 @@ module ActiveRecord
       # Implements the reload reader method, e.g. foo.reload_bar for
       # Foo.has_one :bar
       def force_reload_reader
-        klass.uncached { reload }
+        reload(true)
         target
       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 feacdf6931..0059f0b773 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
@@ -410,16 +410,6 @@ module ActiveRecord
         end
       end
 
-      # The default strategy for an UPDATE with joins is to use a subquery. This doesn't work
-      # on MySQL (even when aliasing the tables), but MySQL allows using JOIN directly in
-      # an UPDATE statement, so in the MySQL adapters we redefine this to do that.
-      def join_to_update(update, select, key) # :nodoc:
-        subselect = subquery_for(key, select)
-
-        update.where key.in(subselect)
-      end
-      alias join_to_delete join_to_update
-
       private
         def default_insert_value(column)
           Arel.sql("DEFAULT")
@@ -460,13 +450,6 @@ module ActiveRecord
           total_sql.join(";\n")
         end
 
-        # Returns a subquery for the given key using the join information.
-        def subquery_for(key, select)
-          subselect = select.clone
-          subselect.projections = [key]
-          subselect
-        end
-
         # Returns an ActiveRecord::Result instance.
         def select(sql, name = nil, binds = [])
           exec_query(sql, name, binds, prepare: false)
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 09242a0f14..d40f38fb77 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -223,18 +223,6 @@ module ActiveRecord
         execute "ROLLBACK"
       end
 
-      # In the simple case, MySQL allows us to place JOINs directly into the UPDATE
-      # query. However, this does not allow for LIMIT, OFFSET and ORDER. To support
-      # these, we must use a subquery.
-      def join_to_update(update, select, key) # :nodoc:
-        if select.limit || select.offset || select.orders.any?
-          super
-        else
-          update.table select.source
-          update.wheres = select.constraints
-        end
-      end
-
       def empty_insert_statement_value(primary_key = nil)
         "VALUES ()"
       end
@@ -733,20 +721,6 @@ module ActiveRecord
           [remove_column_for_alter(table_name, :updated_at), remove_column_for_alter(table_name, :created_at)]
         end
 
-        # MySQL is too stupid to create a temporary table for use subquery, so we have
-        # to give it some prompting in the form of a subsubquery. Ugh!
-        def subquery_for(key, select)
-          subselect = select.clone
-          subselect.projections = [key]
-
-          # Materialize subquery by adding distinct
-          # to work with MySQL 5.7.6 which sets optimizer_switch='derived_merge=on'
-          subselect.distinct unless select.limit || select.offset || select.orders.any?
-
-          key_name = quote_column_name(key.name)
-          Arel::SelectManager.new(subselect.as("__active_record_temp")).project(Arel.sql(key_name))
-        end
-
         def supports_rename_index?
           mariadb? ? false : version >= "5.7.6"
         end
diff --git a/activerecord/lib/active_record/connection_handling.rb b/activerecord/lib/active_record/connection_handling.rb
index 18114f9e1c..5141271db9 100644
--- a/activerecord/lib/active_record/connection_handling.rb
+++ b/activerecord/lib/active_record/connection_handling.rb
@@ -47,6 +47,92 @@ module ActiveRecord
     # The exceptions AdapterNotSpecified, AdapterNotFound and +ArgumentError+
     # may be returned on an error.
     def establish_connection(config_or_env = nil)
+      config_hash = resolve_config_for_connection(config_or_env)
+      connection_handler.establish_connection(config_hash)
+    end
+
+    # Connects a model to the databases specified. The +database+ keyword
+    # takes a hash consisting of a +role+ and a +database_key+.
+    #
+    # This will create a connection handler for switching between connections,
+    # look up the config hash using the +database_key+ and finally
+    # establishes a connection to that config.
+    #
+    #   class AnimalsModel < ApplicationRecord
+    #     self.abstract_class = true
+    #
+    #     connects_to database: { writing: :primary, reading: :primary_replica }
+    #   end
+    #
+    # Returns an array of established connections.
+    def connects_to(database: {})
+      connections = []
+
+      database.each do |role, database_key|
+        config_hash = resolve_config_for_connection(database_key)
+        handler = lookup_connection_handler(role.to_sym)
+
+        connections << handler.establish_connection(config_hash)
+      end
+
+      connections
+    end
+
+    # Connects to a database or role (ex writing, reading, or another
+    # custom role) for the duration of the block.
+    #
+    # If a role is passed, Active Record will look up the connection
+    # based on the requested role:
+    #
+    #   ActiveRecord::Base.connected_to(role: :writing) do
+    #     Dog.create! # creates dog using dog connection
+    #   end
+    #
+    #   ActiveRecord::Base.connected_to(role: :reading) do
+    #     Dog.create! # throws exception because we're on a replica
+    #   end
+    #
+    #   ActiveRecord::Base.connected_to(role: :unknown_ode) do
+    #     # raises exception due to non-existent role
+    #   end
+    #
+    # For cases where you may want to connect to a database outside of the model,
+    # you can use +connected_to+ with a +database+ argument. The +database+ argument
+    # expects a symbol that corresponds to the database key in your config.
+    #
+    # This will connect to a new database for the queries inside the block.
+    #
+    #   ActiveRecord::Base.connected_to(database: :animals_slow_replica) do
+    #     Dog.run_a_long_query # runs a long query while connected to the +animals_slow_replica+
+    #   end
+    def connected_to(database: nil, role: nil, &blk)
+      if database && role
+        raise ArgumentError, "connected_to can only accept a database or role argument, but not both arguments."
+      elsif database
+        config_hash = resolve_config_for_connection(database)
+        handler = lookup_connection_handler(database.to_sym)
+
+        with_handler(database.to_sym) do
+          handler.establish_connection(config_hash)
+          return yield
+        end
+      elsif role
+        with_handler(role.to_sym, &blk)
+      else
+        raise ArgumentError, "must provide a `database` or a `role`."
+      end
+    end
+
+    def lookup_connection_handler(handler_key) # :nodoc:
+      connection_handlers[handler_key] ||= ActiveRecord::ConnectionAdapters::ConnectionHandler.new
+    end
+
+    def with_handler(handler_key, &blk) # :nodoc:
+      handler = lookup_connection_handler(handler_key)
+      swap_connection_handler(handler, &blk)
+    end
+
+    def resolve_config_for_connection(config_or_env) # :nodoc:
       raise "Anonymous class is not allowed." unless name
 
       config_or_env ||= DEFAULT_ENV.call.to_sym
@@ -57,7 +143,7 @@ module ActiveRecord
       config_hash = resolver.resolve(config_or_env, pool_name).symbolize_keys
       config_hash[:name] = pool_name
 
-      connection_handler.establish_connection(config_hash)
+      config_hash
     end
 
     # Returns the connection currently associated with the class. This can
@@ -118,5 +204,14 @@ module ActiveRecord
 
     delegate :clear_active_connections!, :clear_reloadable_connections!,
       :clear_all_connections!, :flush_idle_connections!, to: :connection_handler
+
+    private
+
+      def swap_connection_handler(handler, &blk) # :nodoc:
+        old_handler, ActiveRecord::Base.connection_handler = ActiveRecord::Base.connection_handler, handler
+        yield
+      ensure
+        ActiveRecord::Base.connection_handler = old_handler
+      end
   end
 end
diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index 392602bc0f..b53681ee20 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -124,6 +124,8 @@ module ActiveRecord
 
       mattr_accessor :belongs_to_required_by_default, instance_accessor: false
 
+      mattr_accessor :connection_handlers, instance_accessor: false, default: {}
+
       class_attribute :default_connection_handler, instance_writer: false
 
       self.filter_attributes = []
@@ -137,6 +139,7 @@ module ActiveRecord
       end
 
       self.default_connection_handler = ConnectionAdapters::ConnectionHandler.new
+      self.connection_handlers = { writing: ActiveRecord::Base.default_connection_handler }
     end
 
     module ClassMethods
diff --git a/activerecord/lib/active_record/enum.rb b/activerecord/lib/active_record/enum.rb
index 23ecb24542..3d97e4e513 100644
--- a/activerecord/lib/active_record/enum.rb
+++ b/activerecord/lib/active_record/enum.rb
@@ -150,6 +150,7 @@ module ActiveRecord
       enum_prefix = definitions.delete(:_prefix)
       enum_suffix = definitions.delete(:_suffix)
       definitions.each do |name, values|
+        assert_valid_enum_definition_values(values)
         # statuses = { }
         enum_values = ActiveSupport::HashWithIndifferentAccess.new
         name = name.to_s
@@ -210,10 +211,20 @@ module ActiveRecord
         end
       end
 
+      def assert_valid_enum_definition_values(values)
+        unless values.is_a?(Hash) || values.all? { |v| v.is_a?(Symbol) } || values.all? { |v| v.is_a?(String) }
+          error_message = <<~MSG
+            Enum values #{values} must be either a hash, an array of symbols, or an array of strings.
+          MSG
+          raise ArgumentError, error_message
+        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}."
+      private_constant :ENUM_CONFLICT_MESSAGE
 
       def detect_enum_conflict!(enum_name, method_name, klass_method = false)
         if klass_method && dangerous_class_method?(method_name)
diff --git a/activerecord/lib/active_record/fixture_set/model_metadata.rb b/activerecord/lib/active_record/fixture_set/model_metadata.rb
new file mode 100644
index 0000000000..edc03939c8
--- /dev/null
+++ b/activerecord/lib/active_record/fixture_set/model_metadata.rb
@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  class FixtureSet
+    class ModelMetadata # :nodoc:
+      def initialize(model_class, table_name)
+        @model_class = model_class
+        @table_name  = table_name
+      end
+
+      def primary_key_name
+        @primary_key_name ||= @model_class && @model_class.primary_key
+      end
+
+      def primary_key_type
+        @primary_key_type ||= @model_class && @model_class.type_for_attribute(@model_class.primary_key).type
+      end
+
+      def has_primary_key_column?
+        @has_primary_key_column ||= primary_key_name &&
+          @model_class.columns.any? { |col| col.name == primary_key_name }
+      end
+
+      def timestamp_column_names
+        @timestamp_column_names ||=
+          %w(created_at created_on updated_at updated_on) & column_names
+      end
+
+      def inheritance_column_name
+        @inheritance_column_name ||= @model_class && @model_class.inheritance_column
+      end
+
+      private
+
+        def column_names
+          @column_names ||= @model_class.connection.columns(@table_name).collect(&:name)
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/fixture_set/render_context.rb b/activerecord/lib/active_record/fixture_set/render_context.rb
new file mode 100644
index 0000000000..c90b5343dc
--- /dev/null
+++ b/activerecord/lib/active_record/fixture_set/render_context.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+# NOTE: This class has to be defined in compact style in
+# order for rendering context subclassing to work correctly.
+class ActiveRecord::FixtureSet::RenderContext # :nodoc:
+  def self.create_subclass
+    Class.new(ActiveRecord::FixtureSet.context_class) do
+      def get_binding
+        binding()
+      end
+
+      def binary(path)
+        %(!!binary "#{Base64.strict_encode64(File.read(path))}")
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/fixture_set/table_row.rb b/activerecord/lib/active_record/fixture_set/table_row.rb
new file mode 100644
index 0000000000..5f72c1df38
--- /dev/null
+++ b/activerecord/lib/active_record/fixture_set/table_row.rb
@@ -0,0 +1,79 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  class FixtureSet
+    class TableRow # :nodoc:
+      def initialize(fixture, table_rows:, label:, now:)
+        @table_rows = table_rows
+        @label = label
+        @now = now
+        @row = fixture.to_hash
+        fill_row_model_attributes
+      end
+
+      def to_hash
+        @row
+      end
+
+      private
+
+        def model_metadata
+          @table_rows.model_metadata
+        end
+
+        def model_class
+          @table_rows.model_class
+        end
+
+        def fill_row_model_attributes
+          return unless model_class
+          fill_timestamps
+          interpolate_label
+          generate_primary_key
+          resolve_enums
+          @table_rows.resolve_sti_reflections(@row)
+        end
+
+        def reflection_class
+          @reflection_class ||= if @row.include?(model_metadata.inheritance_column_name)
+            @row[model_metadata.inheritance_column_name].constantize rescue model_class
+          else
+            model_class
+          end
+        end
+
+        def fill_timestamps
+          # fill in timestamp columns if they aren't specified and the model is set to record_timestamps
+          if model_class.record_timestamps
+            model_metadata.timestamp_column_names.each do |c_name|
+              @row[c_name] = @now unless @row.key?(c_name)
+            end
+          end
+        end
+
+        def interpolate_label
+          # interpolate the fixture label
+          @row.each do |key, value|
+            @row[key] = value.gsub("$LABEL", @label.to_s) if value.is_a?(String)
+          end
+        end
+
+        def generate_primary_key
+          # generate a primary key if necessary
+          if model_metadata.has_primary_key_column? && !@row.include?(model_metadata.primary_key_name)
+            @row[model_metadata.primary_key_name] = ActiveRecord::FixtureSet.identify(
+              @label, model_metadata.primary_key_type
+            )
+          end
+        end
+
+        def resolve_enums
+          model_class.defined_enums.each do |name, values|
+            if @row.include?(name)
+              @row[name] = values.fetch(@row[name], @row[name])
+            end
+          end
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/fixture_set/table_rows.rb b/activerecord/lib/active_record/fixture_set/table_rows.rb
new file mode 100644
index 0000000000..e8335a2e10
--- /dev/null
+++ b/activerecord/lib/active_record/fixture_set/table_rows.rb
@@ -0,0 +1,129 @@
+# frozen_string_literal: true
+
+require "active_record/fixture_set/table_row"
+require "active_record/fixture_set/model_metadata"
+
+module ActiveRecord
+  class FixtureSet
+    class TableRows # :nodoc:
+      class ReflectionProxy # :nodoc:
+        def initialize(association)
+          @association = association
+        end
+
+        def join_table
+          @association.join_table
+        end
+
+        def name
+          @association.name
+        end
+
+        def primary_key_type
+          @association.klass.type_for_attribute(@association.klass.primary_key).type
+        end
+      end
+
+      class HasManyThroughProxy < ReflectionProxy # :nodoc:
+        def rhs_key
+          @association.foreign_key
+        end
+
+        def lhs_key
+          @association.through_reflection.foreign_key
+        end
+
+        def join_table
+          @association.through_reflection.table_name
+        end
+      end
+
+      def initialize(table_name, model_class:, fixtures:, config:)
+        @table_name  = table_name
+        @model_class = model_class
+
+        # track any join tables we need to insert later
+        @tables = Hash.new { |h, table| h[table] = [] }
+
+        build_table_rows_from(fixtures, config)
+      end
+
+      attr_reader :table_name, :model_class
+
+      def to_hash
+        @tables.transform_values { |rows| rows.map(&:to_hash) }
+      end
+
+      def model_metadata
+        @model_metadata ||= ModelMetadata.new(model_class, table_name)
+      end
+
+      def resolve_sti_reflections(row)
+        # If STI is used, find the correct subclass for association reflection
+        reflection_class = reflection_class_for(row)
+
+        reflection_class._reflections.each_value do |association|
+          case association.macro
+          when :belongs_to
+            # Do not replace association name with association foreign key if they are named the same
+            fk_name = (association.options[:foreign_key] || "#{association.name}_id").to_s
+
+            if association.name.to_s != fk_name && value = row.delete(association.name.to_s)
+              if association.polymorphic? && value.sub!(/\s*\(([^\)]*)\)\s*$/, "")
+                # support polymorphic belongs_to as "label (Type)"
+                row[association.foreign_type] = $1
+              end
+
+              fk_type = reflection_class.type_for_attribute(fk_name).type
+              row[fk_name] = ActiveRecord::FixtureSet.identify(value, fk_type)
+            end
+          when :has_many
+            if association.options[:through]
+              add_join_records(row, HasManyThroughProxy.new(association))
+            end
+          end
+        end
+      end
+
+      private
+
+        def build_table_rows_from(fixtures, config)
+          now = config.default_timezone == :utc ? Time.now.utc : Time.now
+
+          @tables[table_name] = fixtures.map do |label, fixture|
+            TableRow.new(
+              fixture,
+              table_rows: self,
+              label: label,
+              now: now,
+            )
+          end
+        end
+
+        def reflection_class_for(row)
+          if row.include?(model_metadata.inheritance_column_name)
+            row[model_metadata.inheritance_column_name].constantize rescue model_class
+          else
+            model_class
+          end
+        end
+
+        def add_join_records(row, association)
+          # This is the case when the join table has no fixtures file
+          if (targets = row.delete(association.name.to_s))
+            table_name  = association.join_table
+            column_type = association.primary_key_type
+            lhs_key     = association.lhs_key
+            rhs_key     = association.rhs_key
+
+            targets = targets.is_a?(Array) ? targets : targets.split(/\s*,\s*/)
+            joins   = targets.map do |target|
+              { lhs_key => row[model_metadata.primary_key_name],
+                rhs_key => ActiveRecord::FixtureSet.identify(target, column_type) }
+            end
+            @tables[table_name].concat(joins)
+          end
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/fixtures.rb b/activerecord/lib/active_record/fixtures.rb
index 0d1fdcfb28..b090c76a38 100644
--- a/activerecord/lib/active_record/fixtures.rb
+++ b/activerecord/lib/active_record/fixtures.rb
@@ -7,6 +7,9 @@ require "set"
 require "active_support/dependencies"
 require "active_support/core_ext/digest/uuid"
 require "active_record/fixture_set/file"
+require "active_record/fixture_set/render_context"
+require "active_record/fixture_set/table_rows"
+require "active_record/test_fixtures"
 require "active_record/errors"
 
 module ActiveRecord
@@ -440,60 +443,6 @@ module ActiveRecord
 
     @@all_cached_fixtures = Hash.new { |h, k| h[k] = {} }
 
-    def self.default_fixture_model_name(fixture_set_name, config = ActiveRecord::Base) # :nodoc:
-      config.pluralize_table_names ?
-        fixture_set_name.singularize.camelize :
-        fixture_set_name.camelize
-    end
-
-    def self.default_fixture_table_name(fixture_set_name, config = ActiveRecord::Base) # :nodoc:
-      "#{ config.table_name_prefix }"\
-      "#{ fixture_set_name.tr('/', '_') }"\
-      "#{ config.table_name_suffix }".to_sym
-    end
-
-    def self.reset_cache
-      @@all_cached_fixtures.clear
-    end
-
-    def self.cache_for_connection(connection)
-      @@all_cached_fixtures[connection]
-    end
-
-    def self.fixture_is_cached?(connection, table_name)
-      cache_for_connection(connection)[table_name]
-    end
-
-    def self.cached_fixtures(connection, keys_to_fetch = nil)
-      if keys_to_fetch
-        cache_for_connection(connection).values_at(*keys_to_fetch)
-      else
-        cache_for_connection(connection).values
-      end
-    end
-
-    def self.cache_fixtures(connection, fixtures_map)
-      cache_for_connection(connection).update(fixtures_map)
-    end
-
-    def self.instantiate_fixtures(object, fixture_set, load_instances = true)
-      if load_instances
-        fixture_set.each do |fixture_name, fixture|
-          begin
-            object.instance_variable_set "@#{fixture_name}", fixture.find
-          rescue FixtureClassNotFound
-            nil
-          end
-        end
-      end
-    end
-
-    def self.instantiate_all_loaded_fixtures(object, load_instances = true)
-      all_loaded_fixtures.each_value do |fixture_set|
-        instantiate_fixtures(object, fixture_set, load_instances)
-      end
-    end
-
     cattr_accessor :all_loaded_fixtures, default: {}
 
     class ClassCache
@@ -502,14 +451,16 @@ module ActiveRecord
         @config      = config
 
         # Remove string values that aren't constants or subclasses of AR
-        @class_names.delete_if { |klass_name, klass| !insert_class(@class_names, klass_name, klass) }
+        @class_names.delete_if do |klass_name, klass|
+          !insert_class(@class_names, klass_name, klass)
+        end
       end
 
       def [](fs_name)
-        @class_names.fetch(fs_name) {
+        @class_names.fetch(fs_name) do
           klass = default_fixture_model(fs_name, @config).safe_constantize
           insert_class(@class_names, fs_name, klass)
-        }
+        end
       end
 
       private
@@ -528,38 +479,129 @@ module ActiveRecord
         end
     end
 
-    def self.create_fixtures(fixtures_directory, fixture_set_names, class_names = {}, config = ActiveRecord::Base)
-      fixture_set_names = Array(fixture_set_names).map(&:to_s)
-      class_names = ClassCache.new class_names, config
+    class << self
+      def default_fixture_model_name(fixture_set_name, config = ActiveRecord::Base) # :nodoc:
+        config.pluralize_table_names ?
+          fixture_set_name.singularize.camelize :
+          fixture_set_name.camelize
+      end
 
-      # FIXME: Apparently JK uses this.
-      connection = block_given? ? yield : ActiveRecord::Base.connection
+      def default_fixture_table_name(fixture_set_name, config = ActiveRecord::Base) # :nodoc:
+        "#{ config.table_name_prefix }"\
+        "#{ fixture_set_name.tr('/', '_') }"\
+        "#{ config.table_name_suffix }".to_sym
+      end
 
-      files_to_read = fixture_set_names.reject { |fs_name|
-        fixture_is_cached?(connection, fs_name)
-      }
+      def reset_cache
+        @@all_cached_fixtures.clear
+      end
 
-      unless files_to_read.empty?
-        fixtures_map = {}
+      def cache_for_connection(connection)
+        @@all_cached_fixtures[connection]
+      end
+
+      def fixture_is_cached?(connection, table_name)
+        cache_for_connection(connection)[table_name]
+      end
+
+      def cached_fixtures(connection, keys_to_fetch = nil)
+        if keys_to_fetch
+          cache_for_connection(connection).values_at(*keys_to_fetch)
+        else
+          cache_for_connection(connection).values
+        end
+      end
+
+      def cache_fixtures(connection, fixtures_map)
+        cache_for_connection(connection).update(fixtures_map)
+      end
+
+      def instantiate_fixtures(object, fixture_set, load_instances = true)
+        return unless load_instances
+        fixture_set.each do |fixture_name, fixture|
+          begin
+            object.instance_variable_set "@#{fixture_name}", fixture.find
+          rescue FixtureClassNotFound
+            nil
+          end
+        end
+      end
+
+      def instantiate_all_loaded_fixtures(object, load_instances = true)
+        all_loaded_fixtures.each_value do |fixture_set|
+          instantiate_fixtures(object, fixture_set, load_instances)
+        end
+      end
+
+      def create_fixtures(fixtures_directory, fixture_set_names, class_names = {}, config = ActiveRecord::Base)
+        fixture_set_names = Array(fixture_set_names).map(&:to_s)
+        class_names = ClassCache.new class_names, config
+
+        # FIXME: Apparently JK uses this.
+        connection = block_given? ? yield : ActiveRecord::Base.connection
+
+        fixture_files_to_read = fixture_set_names.reject do |fs_name|
+          fixture_is_cached?(connection, fs_name)
+        end
+
+        if fixture_files_to_read.any?
+          fixtures_map = read_and_insert(
+            fixtures_directory,
+            fixture_files_to_read,
+            class_names,
+            connection,
+          )
+          cache_fixtures(connection, fixtures_map)
+        end
+        cached_fixtures(connection, fixture_set_names)
+      end
 
-        fixture_sets = files_to_read.map do |fs_name|
-          klass = class_names[fs_name]
-          conn = klass ? klass.connection : connection
-          fixtures_map[fs_name] = new( # ActiveRecord::FixtureSet.new
+      # Returns a consistent, platform-independent identifier for +label+.
+      # Integer identifiers are values less than 2^30. UUIDs are RFC 4122 version 5 SHA-1 hashes.
+      def identify(label, column_type = :integer)
+        if column_type == :uuid
+          Digest::UUID.uuid_v5(Digest::UUID::OID_NAMESPACE, label.to_s)
+        else
+          Zlib.crc32(label.to_s) % MAX_ID
+        end
+      end
+
+      # Superclass for the evaluation contexts used by ERB fixtures.
+      def context_class
+        @context_class ||= Class.new
+      end
+
+      private
+
+      def read_and_insert(fixtures_directory, fixture_files, class_names, connection) # :nodoc:
+        fixtures_map = {}
+        fixture_sets = fixture_files.map do |fixture_set_name|
+          klass = class_names[fixture_set_name]
+          conn = klass&.connection || connection
+          fixtures_map[fixture_set_name] = new( # ActiveRecord::FixtureSet.new
             conn,
-            fs_name,
+            fixture_set_name,
             klass,
-            ::File.join(fixtures_directory, fs_name))
+            ::File.join(fixtures_directory, fixture_set_name)
+          )
         end
+        update_all_loaded_fixtures(fixtures_map)
 
-        update_all_loaded_fixtures fixtures_map
-        fixture_sets_by_connection = fixture_sets.group_by { |fs| fs.model_class ? fs.model_class.connection : connection }
+        insert(fixture_sets, connection)
+
+        fixtures_map
+      end
+
+      def insert(fixture_sets, connection) # :nodoc:
+        fixture_sets_by_connection = fixture_sets.group_by do |fixture_set|
+          fixture_set.model_class&.connection || connection
+        end
 
         fixture_sets_by_connection.each do |conn, set|
           table_rows_for_connection = Hash.new { |h, k| h[k] = [] }
 
-          set.each do |fs|
-            fs.table_rows.each do |table, rows|
+          set.each do |fixture_set|
+            fixture_set.table_rows.each do |table, rows|
               table_rows_for_connection[table].unshift(*rows)
             end
           end
@@ -570,31 +612,13 @@ module ActiveRecord
             set.each { |fs| conn.reset_pk_sequence!(fs.table_name) }
           end
         end
-
-        cache_fixtures(connection, fixtures_map)
       end
-      cached_fixtures(connection, fixture_set_names)
-    end
 
-    # Returns a consistent, platform-independent identifier for +label+.
-    # Integer identifiers are values less than 2^30. UUIDs are RFC 4122 version 5 SHA-1 hashes.
-    def self.identify(label, column_type = :integer)
-      if column_type == :uuid
-        Digest::UUID.uuid_v5(Digest::UUID::OID_NAMESPACE, label.to_s)
-      else
-        Zlib.crc32(label.to_s) % MAX_ID
+      def update_all_loaded_fixtures(fixtures_map) # :nodoc:
+        all_loaded_fixtures.update(fixtures_map)
       end
     end
 
-    # Superclass for the evaluation contexts used by ERB fixtures.
-    def self.context_class
-      @context_class ||= Class.new
-    end
-
-    def self.update_all_loaded_fixtures(fixtures_map) # :nodoc:
-      all_loaded_fixtures.update(fixtures_map)
-    end
-
     attr_reader :table_name, :name, :fixtures, :model_class, :config
 
     def initialize(connection, name, class_name, path, config = ActiveRecord::Base)
@@ -632,152 +656,18 @@ module ActiveRecord
     # Returns a hash of rows to be inserted. The key is the table, the value is
     # a list of rows to insert to that table.
     def table_rows
-      now = config.default_timezone == :utc ? Time.now.utc : Time.now
-
       # allow a standard key to be used for doing defaults in YAML
       fixtures.delete("DEFAULTS")
 
-      # track any join tables we need to insert later
-      rows = Hash.new { |h, table| h[table] = [] }
-
-      rows[table_name] = fixtures.map do |label, fixture|
-        row = fixture.to_hash
-
-        if model_class
-          # fill in timestamp columns if they aren't specified and the model is set to record_timestamps
-          if model_class.record_timestamps
-            timestamp_column_names.each do |c_name|
-              row[c_name] = now unless row.key?(c_name)
-            end
-          end
-
-          # interpolate the fixture label
-          row.each do |key, value|
-            row[key] = value.gsub("$LABEL", label.to_s) if value.is_a?(String)
-          end
-
-          # generate a primary key if necessary
-          if has_primary_key_column? && !row.include?(primary_key_name)
-            row[primary_key_name] = ActiveRecord::FixtureSet.identify(label, primary_key_type)
-          end
-
-          # Resolve enums
-          model_class.defined_enums.each do |name, values|
-            if row.include?(name)
-              row[name] = values.fetch(row[name], row[name])
-            end
-          end
-
-          # If STI is used, find the correct subclass for association reflection
-          reflection_class =
-            if row.include?(inheritance_column_name)
-              row[inheritance_column_name].constantize rescue model_class
-            else
-              model_class
-            end
-
-          reflection_class._reflections.each_value do |association|
-            case association.macro
-            when :belongs_to
-              # Do not replace association name with association foreign key if they are named the same
-              fk_name = (association.options[:foreign_key] || "#{association.name}_id").to_s
-
-              if association.name.to_s != fk_name && value = row.delete(association.name.to_s)
-                if association.polymorphic? && value.sub!(/\s*\(([^\)]*)\)\s*$/, "")
-                  # support polymorphic belongs_to as "label (Type)"
-                  row[association.foreign_type] = $1
-                end
-
-                fk_type = reflection_class.type_for_attribute(fk_name).type
-                row[fk_name] = ActiveRecord::FixtureSet.identify(value, fk_type)
-              end
-            when :has_many
-              if association.options[:through]
-                add_join_records(rows, row, HasManyThroughProxy.new(association))
-              end
-            end
-          end
-        end
-
-        row
-      end
-      rows
-    end
-
-    class ReflectionProxy # :nodoc:
-      def initialize(association)
-        @association = association
-      end
-
-      def join_table
-        @association.join_table
-      end
-
-      def name
-        @association.name
-      end
-
-      def primary_key_type
-        @association.klass.type_for_attribute(@association.klass.primary_key).type
-      end
-    end
-
-    class HasManyThroughProxy < ReflectionProxy # :nodoc:
-      def rhs_key
-        @association.foreign_key
-      end
-
-      def lhs_key
-        @association.through_reflection.foreign_key
-      end
-
-      def join_table
-        @association.through_reflection.table_name
-      end
+      TableRows.new(
+        table_name,
+        model_class: model_class,
+        fixtures: fixtures,
+        config: config,
+      ).to_hash
     end
 
     private
-      def primary_key_name
-        @primary_key_name ||= model_class && model_class.primary_key
-      end
-
-      def 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)
-        # This is the case when the join table has no fixtures file
-        if (targets = row.delete(association.name.to_s))
-          table_name  = association.join_table
-          column_type = association.primary_key_type
-          lhs_key     = association.lhs_key
-          rhs_key     = association.rhs_key
-
-          targets = targets.is_a?(Array) ? targets : targets.split(/\s*,\s*/)
-          rows[table_name].concat targets.map { |target|
-            { lhs_key => row[primary_key_name],
-              rhs_key => ActiveRecord::FixtureSet.identify(target, column_type) }
-          }
-        end
-      end
-
-      def has_primary_key_column?
-        @has_primary_key_column ||= primary_key_name &&
-          model_class.columns.any? { |c| c.name == primary_key_name }
-      end
-
-      def timestamp_column_names
-        @timestamp_column_names ||=
-          %w(created_at created_on updated_at updated_on) & column_names
-      end
-
-      def inheritance_column_name
-        @inheritance_column_name ||= model_class && model_class.inheritance_column
-      end
-
-      def column_names
-        @column_names ||= @connection.columns(@table_name).collect(&:name)
-      end
 
       def model_class=(class_name)
         if class_name.is_a?(Class) # TODO: Should be an AR::Base type class, or any?
@@ -841,226 +731,9 @@ module ActiveRecord
     alias :to_hash :fixture
 
     def find
-      if model_class
-        model_class.unscoped do
-          model_class.find(fixture[model_class.primary_key])
-        end
-      else
-        raise FixtureClassNotFound, "No class attached to find."
-      end
-    end
-  end
-end
-
-module ActiveRecord
-  module TestFixtures
-    extend ActiveSupport::Concern
-
-    def before_setup # :nodoc:
-      setup_fixtures
-      super
-    end
-
-    def after_teardown # :nodoc:
-      super
-      teardown_fixtures
-    end
-
-    included do
-      class_attribute :fixture_path, instance_writer: false
-      class_attribute :fixture_table_names, default: []
-      class_attribute :fixture_class_names, default: {}
-      class_attribute :use_transactional_tests, default: true
-      class_attribute :use_instantiated_fixtures, default: false # true, false, or :no_instances
-      class_attribute :pre_loaded_fixtures, default: false
-      class_attribute :config, default: ActiveRecord::Base
-      class_attribute :lock_threads, default: true
-    end
-
-    module ClassMethods
-      # Sets the model class for a fixture when the class name cannot be inferred from the fixture name.
-      #
-      # Examples:
-      #
-      #   set_fixture_class some_fixture:        SomeModel,
-      #                     'namespaced/fixture' => Another::Model
-      #
-      # The keys must be the fixture names, that coincide with the short paths to the fixture files.
-      def set_fixture_class(class_names = {})
-        self.fixture_class_names = fixture_class_names.merge(class_names.stringify_keys)
-      end
-
-      def fixtures(*fixture_set_names)
-        if fixture_set_names.first == :all
-          raise StandardError, "No fixture path found. Please set `#{self}.fixture_path`." if fixture_path.blank?
-          fixture_set_names = Dir["#{fixture_path}/{**,*}/*.{yml}"].uniq
-          fixture_set_names.map! { |f| f[(fixture_path.to_s.size + 1)..-5] }
-        else
-          fixture_set_names = fixture_set_names.flatten.map(&:to_s)
-        end
-
-        self.fixture_table_names |= fixture_set_names
-        setup_fixture_accessors(fixture_set_names)
-      end
-
-      def setup_fixture_accessors(fixture_set_names = nil)
-        fixture_set_names = Array(fixture_set_names || fixture_table_names)
-        methods = Module.new do
-          fixture_set_names.each do |fs_name|
-            fs_name = fs_name.to_s
-            accessor_name = fs_name.tr("/", "_").to_sym
-
-            define_method(accessor_name) do |*fixture_names|
-              force_reload = fixture_names.pop if fixture_names.last == true || fixture_names.last == :reload
-              return_single_record = fixture_names.size == 1
-              fixture_names = @loaded_fixtures[fs_name].fixtures.keys if fixture_names.empty?
-
-              @fixture_cache[fs_name] ||= {}
-
-              instances = fixture_names.map do |f_name|
-                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]
-                  @fixture_cache[fs_name][f_name] ||= @loaded_fixtures[fs_name][f_name].find
-                else
-                  raise StandardError, "No fixture named '#{f_name}' found for fixture set '#{fs_name}'"
-                end
-              end
-
-              return_single_record ? instances.first : instances
-            end
-            private accessor_name
-          end
-        end
-        include methods
-      end
-
-      def uses_transaction(*methods)
-        @uses_transaction = [] unless defined?(@uses_transaction)
-        @uses_transaction.concat methods.map(&:to_s)
-      end
-
-      def uses_transaction?(method)
-        @uses_transaction = [] unless defined?(@uses_transaction)
-        @uses_transaction.include?(method.to_s)
-      end
-    end
-
-    def run_in_transaction?
-      use_transactional_tests &&
-        !self.class.uses_transaction?(method_name)
-    end
-
-    def setup_fixtures(config = ActiveRecord::Base)
-      if pre_loaded_fixtures && !use_transactional_tests
-        raise RuntimeError, "pre_loaded_fixtures requires use_transactional_tests"
-      end
-
-      @fixture_cache = {}
-      @fixture_connections = []
-      @@already_loaded_fixtures ||= {}
-      @connection_subscriber = nil
-
-      # Load fixtures once and begin transaction.
-      if run_in_transaction?
-        if @@already_loaded_fixtures[self.class]
-          @loaded_fixtures = @@already_loaded_fixtures[self.class]
-        else
-          @loaded_fixtures = load_fixtures(config)
-          @@already_loaded_fixtures[self.class] = @loaded_fixtures
-        end
-
-        # Begin transactions for connections already established
-        @fixture_connections = enlist_fixture_connections
-        @fixture_connections.each do |connection|
-          connection.begin_transaction joinable: false
-          connection.pool.lock_thread = true if lock_threads
-        end
-
-        # When connections are established in the future, begin a transaction too
-        @connection_subscriber = ActiveSupport::Notifications.subscribe("!connection.active_record") do |_, _, _, _, payload|
-          spec_name = payload[:spec_name] if payload.key?(:spec_name)
-
-          if spec_name
-            begin
-              connection = ActiveRecord::Base.connection_handler.retrieve_connection(spec_name)
-            rescue ConnectionNotEstablished
-              connection = nil
-            end
-
-            if connection && !@fixture_connections.include?(connection)
-              connection.begin_transaction joinable: false
-              connection.pool.lock_thread = true if lock_threads
-              @fixture_connections << connection
-            end
-          end
-        end
-
-      # Load fixtures for every test.
-      else
-        ActiveRecord::FixtureSet.reset_cache
-        @@already_loaded_fixtures[self.class] = nil
-        @loaded_fixtures = load_fixtures(config)
-      end
-
-      # Instantiate fixtures for every test if requested.
-      instantiate_fixtures if use_instantiated_fixtures
-    end
-
-    def teardown_fixtures
-      # Rollback changes if a transaction is active.
-      if run_in_transaction?
-        ActiveSupport::Notifications.unsubscribe(@connection_subscriber) if @connection_subscriber
-        @fixture_connections.each do |connection|
-          connection.rollback_transaction if connection.transaction_open?
-          connection.pool.lock_thread = false
-        end
-        @fixture_connections.clear
-      else
-        ActiveRecord::FixtureSet.reset_cache
-      end
-
-      ActiveRecord::Base.clear_active_connections!
-    end
-
-    def enlist_fixture_connections
-      ActiveRecord::Base.connection_handler.connection_pool_list.map(&:connection)
-    end
-
-    private
-      def load_fixtures(config)
-        fixtures = ActiveRecord::FixtureSet.create_fixtures(fixture_path, fixture_table_names, fixture_class_names, config)
-        Hash[fixtures.map { |f| [f.name, f] }]
-      end
-
-      def instantiate_fixtures
-        if pre_loaded_fixtures
-          raise RuntimeError, "Load fixtures before instantiating them." if ActiveRecord::FixtureSet.all_loaded_fixtures.empty?
-          ActiveRecord::FixtureSet.instantiate_all_loaded_fixtures(self, load_instances?)
-        else
-          raise RuntimeError, "Load fixtures before instantiating them." if @loaded_fixtures.nil?
-          @loaded_fixtures.each_value do |fixture_set|
-            ActiveRecord::FixtureSet.instantiate_fixtures(self, fixture_set, load_instances?)
-          end
-        end
-      end
-
-      def load_instances?
-        use_instantiated_fixtures != :no_instances
-      end
-  end
-end
-
-class ActiveRecord::FixtureSet::RenderContext # :nodoc:
-  def self.create_subclass
-    Class.new ActiveRecord::FixtureSet.context_class do
-      def get_binding
-        binding()
-      end
-
-      def binary(path)
-        %(!!binary "#{Base64.strict_encode64(File.read(path))}")
+      raise FixtureClassNotFound, "No class attached to find." unless model_class
+      model_class.unscoped do
+        model_class.find(fixture[model_class.primary_key])
       end
     end
   end
diff --git a/activerecord/lib/active_record/integration.rb b/activerecord/lib/active_record/integration.rb
index 6cf26a9792..456689ec6d 100644
--- a/activerecord/lib/active_record/integration.rb
+++ b/activerecord/lib/active_record/integration.rb
@@ -60,7 +60,7 @@ module ActiveRecord
     # the cache key will also include a version.
     #
     #   Product.cache_versioning = false
-    #   Person.find(5).cache_key  # => "people/5-20071224150000" (updated_at available)
+    #   Product.find(5).cache_key  # => "products/5-20071224150000" (updated_at available)
     def cache_key(*timestamp_names)
       if new_record?
         "#{model_name.cache_key}/new"
diff --git a/activerecord/lib/active_record/model_schema.rb b/activerecord/lib/active_record/model_schema.rb
index 9b985e049b..5a4a1fb969 100644
--- a/activerecord/lib/active_record/model_schema.rb
+++ b/activerecord/lib/active_record/model_schema.rb
@@ -218,11 +218,11 @@ module ActiveRecord
       end
 
       def full_table_name_prefix #:nodoc:
-        (parents.detect { |p| p.respond_to?(:table_name_prefix) } || self).table_name_prefix
+        (module_parents.detect { |p| p.respond_to?(:table_name_prefix) } || self).table_name_prefix
       end
 
       def full_table_name_suffix #:nodoc:
-        (parents.detect { |p| p.respond_to?(:table_name_suffix) } || self).table_name_suffix
+        (module_parents.detect { |p| p.respond_to?(:table_name_suffix) } || self).table_name_suffix
       end
 
       # The array of names of environments where destructive actions should be prohibited. By default,
@@ -503,9 +503,9 @@ module ActiveRecord
         def compute_table_name
           if base_class?
             # Nested classes are prefixed with singular parent table name.
-            if parent < Base && !parent.abstract_class?
-              contained = parent.table_name
-              contained = contained.singularize if parent.pluralize_table_names
+            if module_parent < Base && !module_parent.abstract_class?
+              contained = module_parent.table_name
+              contained = contained.singularize if module_parent.pluralize_table_names
               contained += "_"
             end
 
diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index 6eb2bfb452..8404119631 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -758,6 +758,8 @@ module ActiveRecord
       @_association_destroy_exception = nil
     end
 
+    # The name of the method used to touch a +belongs_to+ association when the
+    # +:touch+ option is used.
     def belongs_to_touch_method
       :touch
     end
diff --git a/activerecord/lib/active_record/railtie.rb b/activerecord/lib/active_record/railtie.rb
index 81ad9ef3a2..538659d6bd 100644
--- a/activerecord/lib/active_record/railtie.rb
+++ b/activerecord/lib/active_record/railtie.rb
@@ -168,21 +168,7 @@ end_error
     initializer "active_record.initialize_database" do
       ActiveSupport.on_load(:active_record) do
         self.configurations = Rails.application.config.database_configuration
-
-        begin
-          establish_connection
-        rescue ActiveRecord::NoDatabaseError
-          warn <<-end_warning
-Oops - You have a database configured, but it doesn't exist yet!
-
-Here's how to get started:
-
-  1. Configure your database in config/database.yml.
-  2. Run `rails db:create` to create the database.
-  3. Run `rails db:setup` to load your database schema.
-end_warning
-          raise
-        end
+        establish_connection
       end
     end
 
diff --git a/activerecord/lib/active_record/railties/databases.rake b/activerecord/lib/active_record/railties/databases.rake
index be5ef350a9..1c7ceb4981 100644
--- a/activerecord/lib/active_record/railties/databases.rake
+++ b/activerecord/lib/active_record/railties/databases.rake
@@ -149,18 +149,21 @@ db_namespace = namespace :db do
 
     desc "Display status of migrations"
     task status: :load_config do
-      unless ActiveRecord::SchemaMigration.table_exists?
-        abort "Schema migrations table does not exist yet."
+      ActiveRecord::Base.configurations.configs_for(env_name: Rails.env).each do |db_config|
+        ActiveRecord::Base.establish_connection(db_config.config)
+        ActiveRecord::Tasks::DatabaseTasks.migrate_status
       end
+    end
 
-      # output
-      puts "\ndatabase: #{ActiveRecord::Base.connection_config[:database]}\n\n"
-      puts "#{'Status'.center(8)}  #{'Migration ID'.ljust(14)}  Migration Name"
-      puts "-" * 50
-      ActiveRecord::Base.connection.migration_context.migrations_status.each do |status, version, name|
-        puts "#{status.center(8)}  #{version.ljust(14)}  #{name}"
+    namespace :status do
+      ActiveRecord::Tasks::DatabaseTasks.for_each do |spec_name|
+        desc "Display status of migrations for #{spec_name} database"
+        task spec_name => :load_config do
+          db_config = ActiveRecord::Base.configurations.configs_for(env_name: Rails.env, spec_name: spec_name)
+          ActiveRecord::Base.establish_connection(db_config.config)
+          ActiveRecord::Tasks::DatabaseTasks.migrate_status
+        end
       end
-      puts
     end
   end
 
diff --git a/activerecord/lib/active_record/relation.rb b/activerecord/lib/active_record/relation.rb
index d8cff30b88..d5b6082d13 100644
--- a/activerecord/lib/active_record/relation.rb
+++ b/activerecord/lib/active_record/relation.rb
@@ -348,7 +348,12 @@ module ActiveRecord
       end
 
       stmt = Arel::UpdateManager.new
-      stmt.table(table)
+      stmt.table(arel.join_sources.empty? ? table : arel.source)
+      stmt.key = arel_attribute(primary_key)
+      stmt.take(arel.limit)
+      stmt.offset(arel.offset)
+      stmt.order(*arel.orders)
+      stmt.wheres = arel.constraints
 
       if updates.is_a?(Hash)
         stmt.set _substitute_values(updates)
@@ -356,16 +361,6 @@ module ActiveRecord
         stmt.set Arel.sql(klass.sanitize_sql_for_assignment(updates, table.name))
       end
 
-      if has_join_values?
-        @klass.connection.join_to_update(stmt, arel, arel_attribute(primary_key))
-      else
-        stmt.key = arel_attribute(primary_key)
-        stmt.take(arel.limit)
-        stmt.offset(arel.offset)
-        stmt.order(*arel.orders)
-        stmt.wheres = arel.constraints
-      end
-
       @klass.connection.update stmt, "#{@klass} Update All"
     end
 
@@ -483,17 +478,12 @@ module ActiveRecord
       end
 
       stmt = Arel::DeleteManager.new
-      stmt.from(table)
-
-      if has_join_values?
-        @klass.connection.join_to_delete(stmt, arel, arel_attribute(primary_key))
-      else
-        stmt.key = arel_attribute(primary_key)
-        stmt.take(arel.limit)
-        stmt.offset(arel.offset)
-        stmt.order(*arel.orders)
-        stmt.wheres = arel.constraints
-      end
+      stmt.from(arel.join_sources.empty? ? table : arel.source)
+      stmt.key = arel_attribute(primary_key)
+      stmt.take(arel.limit)
+      stmt.offset(arel.offset)
+      stmt.order(*arel.orders)
+      stmt.wheres = arel.constraints
 
       affected = @klass.connection.delete(stmt, "#{@klass} Destroy")
 
@@ -648,10 +638,6 @@ module ActiveRecord
         end
       end
 
-      def has_join_values?
-        joins_values.any? || left_outer_joins_values.any?
-      end
-
       def exec_queries(&block)
         skip_query_cache_if_necessary do
           @records =
diff --git a/activerecord/lib/active_record/relation/delegation.rb b/activerecord/lib/active_record/relation/delegation.rb
index 8f657840f5..383dc1bf4b 100644
--- a/activerecord/lib/active_record/relation/delegation.rb
+++ b/activerecord/lib/active_record/relation/delegation.rb
@@ -17,6 +17,7 @@ module ActiveRecord
           delegate = Class.new(klass) {
             include ClassSpecificRelation
           }
+          include_relation_methods(delegate)
           mangled_name = klass.name.gsub("::", "_")
           const_set mangled_name, delegate
           private_constant mangled_name
@@ -29,6 +30,35 @@ module ActiveRecord
         child_class.initialize_relation_delegate_cache
         super
       end
+
+      protected
+        def include_relation_methods(delegate)
+          superclass.include_relation_methods(delegate) unless base_class?
+          delegate.include generated_relation_methods
+        end
+
+      private
+        def generated_relation_methods
+          @generated_relation_methods ||= Module.new.tap do |mod|
+            mod_name = "GeneratedRelationMethods"
+            const_set mod_name, mod
+            private_constant mod_name
+          end
+        end
+
+        def generate_relation_method(method)
+          if /\A[a-zA-Z_]\w*[!?]?\z/.match?(method)
+            generated_relation_methods.module_eval <<-RUBY, __FILE__, __LINE__ + 1
+              def #{method}(*args, &block)
+                scoping { klass.#{method}(*args, &block) }
+              end
+            RUBY
+          else
+            generated_relation_methods.send(:define_method, method) do |*args, &block|
+              scoping { klass.public_send(method, *args, &block) }
+            end
+          end
+        end
     end
 
     extend ActiveSupport::Concern
diff --git a/activerecord/lib/active_record/scoping/named.rb b/activerecord/lib/active_record/scoping/named.rb
index 573d97b819..d5cc5db97e 100644
--- a/activerecord/lib/active_record/scoping/named.rb
+++ b/activerecord/lib/active_record/scoping/named.rb
@@ -191,6 +191,8 @@ module ActiveRecord
               scope
             end
           end
+
+          generate_relation_method(name)
         end
 
         private
diff --git a/activerecord/lib/active_record/tasks/database_tasks.rb b/activerecord/lib/active_record/tasks/database_tasks.rb
index 5e29085aff..974d7a1c0a 100644
--- a/activerecord/lib/active_record/tasks/database_tasks.rb
+++ b/activerecord/lib/active_record/tasks/database_tasks.rb
@@ -197,6 +197,21 @@ module ActiveRecord
         Migration.verbose = verbose_was
       end
 
+      def migrate_status
+        unless ActiveRecord::SchemaMigration.table_exists?
+          Kernel.abort "Schema migrations table does not exist yet."
+        end
+
+        # output
+        puts "\ndatabase: #{ActiveRecord::Base.connection_config[:database]}\n\n"
+        puts "#{'Status'.center(8)}  #{'Migration ID'.ljust(14)}  Migration Name"
+        puts "-" * 50
+        ActiveRecord::Base.connection.migration_context.migrations_status.each do |status, version, name|
+          puts "#{status.center(8)}  #{version.ljust(14)}  #{name}"
+        end
+        puts
+      end
+
       def check_target_version
         if target_version && !(Migration::MigrationFilenameRegexp.match?(ENV["VERSION"]) || /\A\d+\z/.match?(ENV["VERSION"]))
           raise "Invalid format of target version: `VERSION=#{ENV['VERSION']}`"
diff --git a/activerecord/lib/active_record/test_fixtures.rb b/activerecord/lib/active_record/test_fixtures.rb
new file mode 100644
index 0000000000..7b7b3f7112
--- /dev/null
+++ b/activerecord/lib/active_record/test_fixtures.rb
@@ -0,0 +1,201 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module TestFixtures
+    extend ActiveSupport::Concern
+
+    def before_setup # :nodoc:
+      setup_fixtures
+      super
+    end
+
+    def after_teardown # :nodoc:
+      super
+      teardown_fixtures
+    end
+
+    included do
+      class_attribute :fixture_path, instance_writer: false
+      class_attribute :fixture_table_names, default: []
+      class_attribute :fixture_class_names, default: {}
+      class_attribute :use_transactional_tests, default: true
+      class_attribute :use_instantiated_fixtures, default: false # true, false, or :no_instances
+      class_attribute :pre_loaded_fixtures, default: false
+      class_attribute :config, default: ActiveRecord::Base
+      class_attribute :lock_threads, default: true
+    end
+
+    module ClassMethods
+      # Sets the model class for a fixture when the class name cannot be inferred from the fixture name.
+      #
+      # Examples:
+      #
+      #   set_fixture_class some_fixture:        SomeModel,
+      #                     'namespaced/fixture' => Another::Model
+      #
+      # The keys must be the fixture names, that coincide with the short paths to the fixture files.
+      def set_fixture_class(class_names = {})
+        self.fixture_class_names = fixture_class_names.merge(class_names.stringify_keys)
+      end
+
+      def fixtures(*fixture_set_names)
+        if fixture_set_names.first == :all
+          raise StandardError, "No fixture path found. Please set `#{self}.fixture_path`." if fixture_path.blank?
+          fixture_set_names = Dir["#{fixture_path}/{**,*}/*.{yml}"].uniq
+          fixture_set_names.map! { |f| f[(fixture_path.to_s.size + 1)..-5] }
+        else
+          fixture_set_names = fixture_set_names.flatten.map(&:to_s)
+        end
+
+        self.fixture_table_names |= fixture_set_names
+        setup_fixture_accessors(fixture_set_names)
+      end
+
+      def setup_fixture_accessors(fixture_set_names = nil)
+        fixture_set_names = Array(fixture_set_names || fixture_table_names)
+        methods = Module.new do
+          fixture_set_names.each do |fs_name|
+            fs_name = fs_name.to_s
+            accessor_name = fs_name.tr("/", "_").to_sym
+
+            define_method(accessor_name) do |*fixture_names|
+              force_reload = fixture_names.pop if fixture_names.last == true || fixture_names.last == :reload
+              return_single_record = fixture_names.size == 1
+              fixture_names = @loaded_fixtures[fs_name].fixtures.keys if fixture_names.empty?
+
+              @fixture_cache[fs_name] ||= {}
+
+              instances = fixture_names.map do |f_name|
+                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]
+                  @fixture_cache[fs_name][f_name] ||= @loaded_fixtures[fs_name][f_name].find
+                else
+                  raise StandardError, "No fixture named '#{f_name}' found for fixture set '#{fs_name}'"
+                end
+              end
+
+              return_single_record ? instances.first : instances
+            end
+            private accessor_name
+          end
+        end
+        include methods
+      end
+
+      def uses_transaction(*methods)
+        @uses_transaction = [] unless defined?(@uses_transaction)
+        @uses_transaction.concat methods.map(&:to_s)
+      end
+
+      def uses_transaction?(method)
+        @uses_transaction = [] unless defined?(@uses_transaction)
+        @uses_transaction.include?(method.to_s)
+      end
+    end
+
+    def run_in_transaction?
+      use_transactional_tests &&
+        !self.class.uses_transaction?(method_name)
+    end
+
+    def setup_fixtures(config = ActiveRecord::Base)
+      if pre_loaded_fixtures && !use_transactional_tests
+        raise RuntimeError, "pre_loaded_fixtures requires use_transactional_tests"
+      end
+
+      @fixture_cache = {}
+      @fixture_connections = []
+      @@already_loaded_fixtures ||= {}
+      @connection_subscriber = nil
+
+      # Load fixtures once and begin transaction.
+      if run_in_transaction?
+        if @@already_loaded_fixtures[self.class]
+          @loaded_fixtures = @@already_loaded_fixtures[self.class]
+        else
+          @loaded_fixtures = load_fixtures(config)
+          @@already_loaded_fixtures[self.class] = @loaded_fixtures
+        end
+
+        # Begin transactions for connections already established
+        @fixture_connections = enlist_fixture_connections
+        @fixture_connections.each do |connection|
+          connection.begin_transaction joinable: false
+          connection.pool.lock_thread = true if lock_threads
+        end
+
+        # When connections are established in the future, begin a transaction too
+        @connection_subscriber = ActiveSupport::Notifications.subscribe("!connection.active_record") do |_, _, _, _, payload|
+          spec_name = payload[:spec_name] if payload.key?(:spec_name)
+
+          if spec_name
+            begin
+              connection = ActiveRecord::Base.connection_handler.retrieve_connection(spec_name)
+            rescue ConnectionNotEstablished
+              connection = nil
+            end
+
+            if connection && !@fixture_connections.include?(connection)
+              connection.begin_transaction joinable: false
+              connection.pool.lock_thread = true if lock_threads
+              @fixture_connections << connection
+            end
+          end
+        end
+
+      # Load fixtures for every test.
+      else
+        ActiveRecord::FixtureSet.reset_cache
+        @@already_loaded_fixtures[self.class] = nil
+        @loaded_fixtures = load_fixtures(config)
+      end
+
+      # Instantiate fixtures for every test if requested.
+      instantiate_fixtures if use_instantiated_fixtures
+    end
+
+    def teardown_fixtures
+      # Rollback changes if a transaction is active.
+      if run_in_transaction?
+        ActiveSupport::Notifications.unsubscribe(@connection_subscriber) if @connection_subscriber
+        @fixture_connections.each do |connection|
+          connection.rollback_transaction if connection.transaction_open?
+          connection.pool.lock_thread = false
+        end
+        @fixture_connections.clear
+      else
+        ActiveRecord::FixtureSet.reset_cache
+      end
+
+      ActiveRecord::Base.clear_active_connections!
+    end
+
+    def enlist_fixture_connections
+      ActiveRecord::Base.connection_handler.connection_pool_list.map(&:connection)
+    end
+
+    private
+      def load_fixtures(config)
+        fixtures = ActiveRecord::FixtureSet.create_fixtures(fixture_path, fixture_table_names, fixture_class_names, config)
+        Hash[fixtures.map { |f| [f.name, f] }]
+      end
+
+      def instantiate_fixtures
+        if pre_loaded_fixtures
+          raise RuntimeError, "Load fixtures before instantiating them." if ActiveRecord::FixtureSet.all_loaded_fixtures.empty?
+          ActiveRecord::FixtureSet.instantiate_all_loaded_fixtures(self, load_instances?)
+        else
+          raise RuntimeError, "Load fixtures before instantiating them." if @loaded_fixtures.nil?
+          @loaded_fixtures.each_value do |fixture_set|
+            ActiveRecord::FixtureSet.instantiate_fixtures(self, fixture_set, load_instances?)
+          end
+        end
+      end
+
+      def load_instances?
+        use_instantiated_fixtures != :no_instances
+      end
+  end
+end