Merge branch 'master' into unlock-minitest

25 files changed, 123 insertions, 121 deletions

diff --git a/activerecord/lib/active_record/associations/alias_tracker.rb b/activerecord/lib/active_record/associations/alias_tracker.rb
index 3963008a76..4a5c821607 100644
--- a/activerecord/lib/active_record/associations/alias_tracker.rb
+++ b/activerecord/lib/active_record/associations/alias_tracker.rb
@@ -4,8 +4,6 @@ module ActiveRecord
   module Associations
     # Keeps track of table aliases for ActiveRecord::Associations::JoinDependency
     class AliasTracker # :nodoc:
-      attr_reader :aliases
-
       def self.create(connection, initial_table, type_caster)
         aliases = Hash.new(0)
         aliases[initial_table] = 1
@@ -80,6 +78,11 @@ module ActiveRecord
         end
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
+      protected
+        attr_reader :aliases
+
       private
 
         def truncate(name)
diff --git a/activerecord/lib/active_record/associations/association.rb b/activerecord/lib/active_record/associations/association.rb
index 6b13e6936f..ee2e79889f 100644
--- a/activerecord/lib/active_record/associations/association.rb
+++ b/activerecord/lib/active_record/associations/association.rb
@@ -133,6 +133,16 @@ module ActiveRecord
         AssociationRelation.create(klass, klass.arel_table, klass.predicate_builder, self).merge!(klass.all)
       end
 
+      def extensions
+        extensions = klass.default_extensions | reflection.extensions
+
+        if scope = reflection.scope
+          extensions |= klass.unscoped.instance_exec(owner, &scope).extensions
+        end
+
+        extensions
+      end
+
       # Loads the \target if needed and returns it.
       #
       # This method is abstract in the sense that it relies on +find_target+,
diff --git a/activerecord/lib/active_record/associations/association_scope.rb b/activerecord/lib/active_record/associations/association_scope.rb
index 120d75416c..1593b94f0c 100644
--- a/activerecord/lib/active_record/associations/association_scope.rb
+++ b/activerecord/lib/active_record/associations/association_scope.rb
@@ -24,7 +24,7 @@ module ActiveRecord
         alias_tracker = AliasTracker.create connection, association.klass.table_name, klass.type_caster
         chain_head, chain_tail = get_chain(reflection, association, alias_tracker)
 
-        scope.extending! Array(reflection.options[:extend])
+        scope.extending! reflection.extensions
         add_constraints(scope, owner, reflection, chain_head, chain_tail)
       end
 
diff --git a/activerecord/lib/active_record/associations/collection_association.rb b/activerecord/lib/active_record/associations/collection_association.rb
index 62c944fce3..edc53e2517 100644
--- a/activerecord/lib/active_record/associations/collection_association.rb
+++ b/activerecord/lib/active_record/associations/collection_association.rb
@@ -30,7 +30,8 @@ module ActiveRecord
           reload
         end
 
-        CollectionProxy.create(klass, self)
+        @proxy ||= CollectionProxy.create(klass, self)
+        @proxy.reset_scope
       end
 
       # Implements the writer method, e.g. foo.items= for Foo.has_many :items
diff --git a/activerecord/lib/active_record/associations/collection_proxy.rb b/activerecord/lib/active_record/associations/collection_proxy.rb
index 74a4d515c2..8cdb508c43 100644
--- a/activerecord/lib/active_record/associations/collection_proxy.rb
+++ b/activerecord/lib/active_record/associations/collection_proxy.rb
@@ -31,6 +31,9 @@ module ActiveRecord
       def initialize(klass, association) #:nodoc:
         @association = association
         super klass, klass.arel_table, klass.predicate_builder
+
+        extensions = association.extensions
+        extend(*extensions) if extensions.any?
       end
 
       def target
@@ -1084,9 +1087,8 @@ module ActiveRecord
       #   person.pets(true)  # fetches pets from the database
       #   # => [#<Pet id: 1, name: "Snoop", group: "dogs", person_id: 1>]
       def reload
-        @scope = nil
         proxy_association.reload
-        self
+        reset_scope
       end
 
       # Unloads the association. Returns +self+.
@@ -1106,9 +1108,13 @@ module ActiveRecord
       #   person.pets  # fetches pets from the database
       #   # => [#<Pet id: 1, name: "Snoop", group: "dogs", person_id: 1>]
       def reset
-        @scope = nil
         proxy_association.reset
         proxy_association.reset_scope
+        reset_scope
+      end
+
+      def reset_scope # :nodoc:
+        @scope = nil
         self
       end
 
@@ -1121,19 +1127,6 @@ module ActiveRecord
 
       delegate(*delegate_methods, to: :scope)
 
-      module DelegateExtending # :nodoc:
-        private
-          def method_missing(method, *args, &block)
-            extending_values = association_scope.extending_values
-            if extending_values.any? && (extending_values - self.class.included_modules).any?
-              self.class.include(*extending_values)
-              public_send(method, *args, &block)
-            else
-              super
-            end
-          end
-      end
-
       private
 
         def find_nth_with_limit(index, limit)
@@ -1154,17 +1147,9 @@ module ActiveRecord
           @association.find_from_target?
         end
 
-        def association_scope
-          @association.association_scope
-        end
-
         def exec_queries
           load_target
         end
-
-        def respond_to_missing?(method, _)
-          association_scope.respond_to?(method) || super
-        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/associations/preloader/association.rb b/activerecord/lib/active_record/associations/preloader/association.rb
index 4072d19380..63ef3f2d8c 100644
--- a/activerecord/lib/active_record/associations/preloader/association.rb
+++ b/activerecord/lib/active_record/associations/preloader/association.rb
@@ -51,11 +51,10 @@ module ActiveRecord
           raise NotImplementedError
         end
 
-        def options
-          reflection.options
-        end
-
         private
+          def options
+            reflection.options
+          end
 
           def associated_records_by_owner(preloader)
             records = load_records do |record|
diff --git a/activerecord/lib/active_record/associations/preloader/belongs_to.rb b/activerecord/lib/active_record/associations/preloader/belongs_to.rb
index 38e231826c..c20145770f 100644
--- a/activerecord/lib/active_record/associations/preloader/belongs_to.rb
+++ b/activerecord/lib/active_record/associations/preloader/belongs_to.rb
@@ -3,7 +3,7 @@ module ActiveRecord
     class Preloader
       class BelongsTo < SingularAssociation #:nodoc:
         def association_key_name
-          reflection.options[:primary_key] || klass && klass.primary_key
+          options[:primary_key] || klass && klass.primary_key
         end
 
         def owner_key_name
diff --git a/activerecord/lib/active_record/associations/preloader/through_association.rb b/activerecord/lib/active_record/associations/preloader/through_association.rb
index d53d3f777b..8b954138cd 100644
--- a/activerecord/lib/active_record/associations/preloader/through_association.rb
+++ b/activerecord/lib/active_record/associations/preloader/through_association.rb
@@ -65,7 +65,7 @@ module ActiveRecord
 
           def reset_association(owners, association_name)
             should_reset = (through_scope != through_reflection.klass.unscoped) ||
-               (reflection.options[:source_type] && through_reflection.collection?)
+               (options[:source_type] && through_reflection.collection?)
 
             # Don't cache the association - we would only be caching a subset
             if should_reset
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 9cb7c46df5..648c869915 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -543,7 +543,7 @@ module ActiveRecord
           m.register_type %r(longblob)i,   Type::Binary.new(limit: 2**32 - 1)
           m.register_type %r(^float)i,     Type::Float.new(limit: 24)
           m.register_type %r(^double)i,    Type::Float.new(limit: 53)
-          m.register_type %r(^json)i,      MysqlJson.new
+          m.register_type %r(^json)i,      Type::Json.new
 
           register_integer_type m, %r(^bigint)i,    limit: 8
           register_integer_type m, %r(^int)i,       limit: 4
@@ -837,12 +837,7 @@ module ActiveRecord
           end
         end
 
-        class MysqlJson < Type::Internal::AbstractJson # :nodoc:
-          def changed_in_place?(raw_old_value, new_value)
-            # Normalization is required because MySQL JSON data format includes
-            # the space between the elements.
-            super(serialize(deserialize(raw_old_value)), new_value)
-          end
+        class MysqlJson < Type::Json # :nodoc:
         end
 
         class MysqlString < Type::String # :nodoc:
@@ -865,7 +860,6 @@ module ActiveRecord
             end
         end
 
-        ActiveRecord::Type.register(:json, MysqlJson, adapter: :mysql2)
         ActiveRecord::Type.register(:string, MysqlString, adapter: :mysql2)
         ActiveRecord::Type.register(:unsigned_integer, Type::UnsignedInteger, adapter: :mysql2)
     end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb
index dbc879ffd4..3c706c27c4 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb
@@ -2,7 +2,7 @@ module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
       module OID # :nodoc:
-        class Json < Type::Internal::AbstractJson
+        class Json < Type::Json # :nodoc:
         end
       end
     end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/jsonb.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/jsonb.rb
index 87391b5dc7..a1fec289d4 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/jsonb.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/jsonb.rb
@@ -2,20 +2,10 @@ module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
       module OID # :nodoc:
-        class Jsonb < Json # :nodoc:
+        class Jsonb < Type::Json # :nodoc:
           def type
             :jsonb
           end
-
-          def changed_in_place?(raw_old_value, new_value)
-            # Postgres does not preserve insignificant whitespaces when
-            # round-tripping jsonb columns. This causes some false positives for
-            # the comparison here. Therefore, we need to parse and re-dump the
-            # raw value here to ensure the insignificant whitespaces are
-            # consistent with our encoder's output.
-            raw_old_value = serialize(deserialize(raw_old_value))
-            super(raw_old_value, new_value)
-          end
         end
       end
     end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb b/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb
index da8d0c6992..44eb666965 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb
@@ -62,7 +62,7 @@ module ActiveRecord
         def quote_default_expression(value, column) # :nodoc:
           if value.is_a?(Proc)
             value.call
-          elsif column.type == :uuid && value.include?("()")
+          elsif column.type == :uuid && /\(\)/.match?(value)
             value # Does not quote function default values for UUID columns
           elsif column.respond_to?(:array?)
             value = type_cast_from_column(column, value)
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
index 55566f1e34..cb45d7ba6b 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
@@ -290,9 +290,17 @@ module ActiveRecord
 
           if pk && sequence
             quoted_sequence = quote_table_name(sequence)
+            max_pk = select_value("select MAX(#{quote_column_name pk}) from #{quote_table_name(table)}")
+            if max_pk.nil?
+              if postgresql_version >= 100000
+                minvalue = select_value("SELECT seqmin from pg_sequence where seqrelid = '#{quoted_sequence}'::regclass")
+              else
+                minvalue = select_value("SELECT min_value FROM #{quoted_sequence}")
+              end
+            end
 
             select_value(<<-end_sql, "SCHEMA")
-              SELECT setval('#{quoted_sequence}', (SELECT COALESCE(MAX(#{quote_column_name pk})+(SELECT increment_by FROM #{quoted_sequence}), (SELECT min_value FROM #{quoted_sequence})) FROM #{quote_table_name(table)}), false)
+              SELECT setval('#{quoted_sequence}', #{max_pk ? max_pk : minvalue}, #{max_pk ? true : false})
             end_sql
           end
         end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index f74f966fd9..5287dd6a51 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -458,7 +458,7 @@ module ActiveRecord
           m.register_type "bytea", OID::Bytea.new
           m.register_type "point", OID::Point.new
           m.register_type "hstore", OID::Hstore.new
-          m.register_type "json", OID::Json.new
+          m.register_type "json", Type::Json.new
           m.register_type "jsonb", OID::Jsonb.new
           m.register_type "cidr", OID::Cidr.new
           m.register_type "inet", OID::Inet.new
@@ -843,7 +843,6 @@ module ActiveRecord
         ActiveRecord::Type.register(:enum, OID::Enum, adapter: :postgresql)
         ActiveRecord::Type.register(:hstore, OID::Hstore, adapter: :postgresql)
         ActiveRecord::Type.register(:inet, OID::Inet, adapter: :postgresql)
-        ActiveRecord::Type.register(:json, OID::Json, adapter: :postgresql)
         ActiveRecord::Type.register(:jsonb, OID::Jsonb, adapter: :postgresql)
         ActiveRecord::Type.register(:money, OID::Money, adapter: :postgresql)
         ActiveRecord::Type.register(:point, OID::Point, adapter: :postgresql)
diff --git a/activerecord/lib/active_record/querying.rb b/activerecord/lib/active_record/querying.rb
index c4a22398f0..b16e178358 100644
--- a/activerecord/lib/active_record/querying.rb
+++ b/activerecord/lib/active_record/querying.rb
@@ -8,7 +8,7 @@ module ActiveRecord
     delegate :destroy, :destroy_all, :delete, :delete_all, :update, :update_all, to: :all
     delegate :find_each, :find_in_batches, :in_batches, to: :all
     delegate :select, :group, :order, :except, :reorder, :limit, :offset, :joins, :left_joins, :left_outer_joins, :or,
-             :where, :rewhere, :preload, :eager_load, :includes, :from, :lock, :readonly,
+             :where, :rewhere, :preload, :eager_load, :includes, :from, :lock, :readonly, :extending,
              :having, :create_with, :distinct, :references, :none, :unscope, :merge, to: :all
     delegate :count, :average, :minimum, :maximum, :sum, :calculate, to: :all
     delegate :pluck, :ids, to: :all
diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index d6154c9a38..e8ee8279fd 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -287,6 +287,11 @@ module ActiveRecord
         JoinKeys.new(join_pk(association_klass), join_fk)
       end
 
+      protected
+        def actual_source_reflection # FIXME: this is a horrible name
+          self
+        end
+
       private
 
         def join_pk(_)
@@ -579,11 +584,9 @@ module ActiveRecord
         seed + [self]
       end
 
-      protected
-
-        def actual_source_reflection # FIXME: this is a horrible name
-          self
-        end
+      def extensions
+        Array(options[:extend])
+      end
 
       private
 
@@ -757,7 +760,6 @@ module ActiveRecord
     # Holds all the metadata about a :through association as it was specified
     # in the Active Record class.
     class ThroughReflection < AbstractReflection #:nodoc:
-      attr_reader :delegate_reflection
       delegate :foreign_key, :foreign_type, :association_foreign_key,
                :active_record_primary_key, :type, :get_join_keys, to: :source_reflection
 
@@ -983,19 +985,23 @@ module ActiveRecord
         collect_join_reflections(seed + [self])
       end
 
-      def collect_join_reflections(seed)
-        a = source_reflection.add_as_source seed
-        if options[:source_type]
-          through_reflection.add_as_polymorphic_through self, a
-        else
-          through_reflection.add_as_through a
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
+      protected
+        attr_reader :delegate_reflection
+
+        def actual_source_reflection # FIXME: this is a horrible name
+          source_reflection.actual_source_reflection
         end
-      end
 
       private
-
-        def actual_source_reflection # FIXME: this is a horrible name
-          source_reflection.send(:actual_source_reflection)
+        def collect_join_reflections(seed)
+          a = source_reflection.add_as_source seed
+          if options[:source_type]
+            through_reflection.add_as_polymorphic_through self, a
+          else
+            through_reflection.add_as_through a
+          end
         end
 
         def primary_key(klass)
diff --git a/activerecord/lib/active_record/relation/delegation.rb b/activerecord/lib/active_record/relation/delegation.rb
index 4f739a0415..dada0fddf8 100644
--- a/activerecord/lib/active_record/relation/delegation.rb
+++ b/activerecord/lib/active_record/relation/delegation.rb
@@ -25,8 +25,6 @@ module ActiveRecord
 
       def inherited(child_class)
         child_class.initialize_relation_delegate_cache
-        delegate = child_class.relation_delegate_class(ActiveRecord::Associations::CollectionProxy)
-        delegate.include ActiveRecord::Associations::CollectionProxy::DelegateExtending
         super
       end
     end
diff --git a/activerecord/lib/active_record/relation/predicate_builder/association_query_value.rb b/activerecord/lib/active_record/relation/predicate_builder/association_query_value.rb
index 2fe0f81cab..3e19646ae5 100644
--- a/activerecord/lib/active_record/relation/predicate_builder/association_query_value.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder/association_query_value.rb
@@ -1,8 +1,6 @@
 module ActiveRecord
   class PredicateBuilder
     class AssociationQueryValue # :nodoc:
-      attr_reader :associated_table, :value
-
       def initialize(associated_table, value)
         @associated_table = associated_table
         @value = value
@@ -12,6 +10,11 @@ module ActiveRecord
         [associated_table.association_foreign_key.to_s => ids]
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
+      protected
+        attr_reader :associated_table, :value
+
       private
         def ids
           case value
diff --git a/activerecord/lib/active_record/relation/predicate_builder/polymorphic_array_value.rb b/activerecord/lib/active_record/relation/predicate_builder/polymorphic_array_value.rb
index 9bb2f8c8dc..7029ae5f47 100644
--- a/activerecord/lib/active_record/relation/predicate_builder/polymorphic_array_value.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder/polymorphic_array_value.rb
@@ -1,8 +1,6 @@
 module ActiveRecord
   class PredicateBuilder
     class PolymorphicArrayValue # :nodoc:
-      attr_reader :associated_table, :values
-
       def initialize(associated_table, values)
         @associated_table = associated_table
         @values = values
@@ -17,6 +15,11 @@ module ActiveRecord
         end
       end
 
+      # TODO Change this to private once we've dropped Ruby 2.2 support.
+      # Workaround for Ruby 2.2 "private attribute?" warning.
+      protected
+        attr_reader :associated_table, :values
+
       private
         def type_to_ids_mapping
           default_hash = Hash.new { |hsh, key| hsh[key] = [] }
diff --git a/activerecord/lib/active_record/scoping/default.rb b/activerecord/lib/active_record/scoping/default.rb
index ba5cc29ac1..70b2693b28 100644
--- a/activerecord/lib/active_record/scoping/default.rb
+++ b/activerecord/lib/active_record/scoping/default.rb
@@ -107,7 +107,11 @@ module ActiveRecord
 
             if default_scope_override
               # The user has defined their own default scope method, so call that
-              evaluate_default_scope { default_scope }
+              evaluate_default_scope do
+                if scope = default_scope
+                  (base_rel ||= relation).merge(scope)
+                end
+              end
             elsif default_scopes.any?
               base_rel ||= relation
               evaluate_default_scope do
diff --git a/activerecord/lib/active_record/scoping/named.rb b/activerecord/lib/active_record/scoping/named.rb
index 029156189d..a61fdd6454 100644
--- a/activerecord/lib/active_record/scoping/named.rb
+++ b/activerecord/lib/active_record/scoping/named.rb
@@ -30,12 +30,15 @@ module ActiveRecord
         end
 
         def default_scoped # :nodoc:
-          scope = build_default_scope
+          scope = relation
+          build_default_scope(scope) || scope
+        end
 
-          if scope
-            relation.spawn.merge!(scope)
+        def default_extensions # :nodoc:
+          if scope = current_scope || build_default_scope
+            scope.extensions
           else
-            relation
+            []
           end
         end
 
diff --git a/activerecord/lib/active_record/tasks/sqlite_database_tasks.rb b/activerecord/lib/active_record/tasks/sqlite_database_tasks.rb
index 7043d2f0c8..01562b21e9 100644
--- a/activerecord/lib/active_record/tasks/sqlite_database_tasks.rb
+++ b/activerecord/lib/active_record/tasks/sqlite_database_tasks.rb
@@ -42,7 +42,7 @@ module ActiveRecord
 
         ignore_tables = ActiveRecord::SchemaDumper.ignore_tables
         if ignore_tables.any?
-          condition = ignore_tables.map { |table| connection.quote_table_name(table) }.join(", ")
+          condition = ignore_tables.map { |table| connection.quote(table) }.join(", ")
           args << "SELECT sql FROM sqlite_master WHERE tbl_name NOT IN (#{condition}) ORDER BY tbl_name, type DESC, name"
         else
           args << ".schema"
diff --git a/activerecord/lib/active_record/type.rb b/activerecord/lib/active_record/type.rb
index 4f632660a8..9ed6c95bf9 100644
--- a/activerecord/lib/active_record/type.rb
+++ b/activerecord/lib/active_record/type.rb
@@ -1,11 +1,11 @@
 require "active_model/type"
 
-require "active_record/type/internal/abstract_json"
 require "active_record/type/internal/timezone"
 
 require "active_record/type/date"
 require "active_record/type/date_time"
 require "active_record/type/decimal_without_scale"
+require "active_record/type/json"
 require "active_record/type/time"
 require "active_record/type/text"
 require "active_record/type/unsigned_integer"
@@ -69,6 +69,7 @@ module ActiveRecord
     register(:decimal, Type::Decimal, override: false)
     register(:float, Type::Float, override: false)
     register(:integer, Type::Integer, override: false)
+    register(:json, Type::Json, override: false)
     register(:string, Type::String, override: false)
     register(:text, Type::Text, override: false)
     register(:time, Type::Time, override: false)
diff --git a/activerecord/lib/active_record/type/internal/abstract_json.rb b/activerecord/lib/active_record/type/internal/abstract_json.rb
deleted file mode 100644
index e19c5a14da..0000000000
--- a/activerecord/lib/active_record/type/internal/abstract_json.rb
+++ /dev/null
@@ -1,33 +0,0 @@
-module ActiveRecord
-  module Type
-    module Internal # :nodoc:
-      class AbstractJson < ActiveModel::Type::Value # :nodoc:
-        include ActiveModel::Type::Helpers::Mutable
-
-        def type
-          :json
-        end
-
-        def deserialize(value)
-          if value.is_a?(::String)
-            ::ActiveSupport::JSON.decode(value) rescue nil
-          else
-            value
-          end
-        end
-
-        def serialize(value)
-          if value.nil?
-            nil
-          else
-            ::ActiveSupport::JSON.encode(value)
-          end
-        end
-
-        def accessor
-          ActiveRecord::Store::StringKeyedHashAccessor
-        end
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/type/json.rb b/activerecord/lib/active_record/type/json.rb
new file mode 100644
index 0000000000..c4732fe388
--- /dev/null
+++ b/activerecord/lib/active_record/type/json.rb
@@ -0,0 +1,28 @@
+module ActiveRecord
+  module Type
+    class Json < ActiveModel::Type::Value
+      include ActiveModel::Type::Helpers::Mutable
+
+      def type
+        :json
+      end
+
+      def deserialize(value)
+        return value unless value.is_a?(::String)
+        ActiveSupport::JSON.decode(value) rescue nil
+      end
+
+      def serialize(value)
+        ActiveSupport::JSON.encode(value) unless value.nil?
+      end
+
+      def changed_in_place?(raw_old_value, new_value)
+        deserialize(raw_old_value) != new_value
+      end
+
+      def accessor
+        ActiveRecord::Store::StringKeyedHashAccessor
+      end
+    end
+  end
+end