Merge pull request rails#46231 from jonathanhefner/active_model-memoize-value_for_database

Avoid unnecessary `serialize` calls after save

Author: jonathanhefner

activemodel/lib/active_model/attribute.rb

@@ -53,7 +53,10 @@ def original_value
     end
 
     def value_for_database
-      type.serialize(value)
+      if !defined?(@value_for_database) || type.changed_in_place?(@value_for_database, value)
+        @value_for_database = _value_for_database
+      end
+      @value_for_database
     end
 
     def serializable?(&block)
@@ -159,6 +162,10 @@ def changed_from_assignment?
         assigned? && type.changed?(original_value, value, value_before_type_cast)
       end
 
+      def _value_for_database
+        type.serialize(value)
+      end
+
       def _original_value_for_database
         type.serialize(original_value)
       end
@@ -179,13 +186,14 @@ def type_cast(value)
           type.cast(value)
         end
 
-        def value_for_database
-          Type::SerializeCastValue.serialize(type, value)
-        end
-
         def came_from_user?
           !type.value_constructed_by_mass_assignment?(value_before_type_cast)
         end
+
+        private
+          def _value_for_database
+            Type::SerializeCastValue.serialize(type, value)
+          end
       end
 
       class WithCastValue < Attribute # :nodoc:

activemodel/test/cases/attribute_test.rb

@@ -5,6 +5,10 @@
 module ActiveModel
   class AttributeTest < ActiveModel::TestCase
     class InscribingType
+      def changed_in_place?(raw_old_value, new_value)
+        false
+      end
+
       def cast(value)
         "cast(#{value})"
       end
@@ -96,6 +100,37 @@ def serialize_cast_value(value)
       assert_equal "serialize_cast_value(cast(whatever))", attribute.value_for_database
     end
 
+    test "value_for_database is memoized" do
+      count = 0
+      @type.define_singleton_method(:serialize) do |value|
+        count += 1
+        nil
+      end
+
+      attribute = Attribute.from_user(nil, "whatever", @type)
+
+      attribute.value_for_database
+      attribute.value_for_database
+      assert_equal 1, count
+    end
+
+    test "value_for_database is recomputed when value changes in place" do
+      count = 0
+      @type.define_singleton_method(:serialize) do |value|
+        count += 1
+        nil
+      end
+      @type.define_singleton_method(:changed_in_place?) do |*|
+        true
+      end
+
+      attribute = Attribute.from_user(nil, "whatever", @type)
+
+      attribute.value_for_database
+      attribute.value_for_database
+      assert_equal 2, count
+    end
+
     test "duping dups the value" do
       attribute = Attribute.from_database(nil, "a value", @type)
 

activerecord/lib/active_record/relation/query_attribute.rb

@@ -10,7 +10,8 @@ def type_cast(value)
       end
 
       def value_for_database
-        @value_for_database ||= super
+        @value_for_database = _value_for_database unless defined?(@value_for_database)
+        @value_for_database
       end
 
       def with_cast_value(value)