Merge pull request #47191 from serg-kovalev/fix/issue-46351-serialize…

…-default

Respect Column default in Type::Serialized

activerecord/lib/active_record/attribute_methods/serialization.rb

@@ -127,7 +127,7 @@ def serialize(attr_name, class_name_or_coder = Object, yaml: {}, **options)
             end
 
             cast_type = cast_type.subtype if Type::Serialized === cast_type
-            Type::Serialized.new(cast_type, coder)
+            Type::Serialized.new(cast_type, coder, default: columns_hash[attr_name.to_s]&.default)
           end
         end
 

activerecord/lib/active_record/type/serialized.rb

@@ -9,9 +9,10 @@ class Serialized < DelegateClass(ActiveModel::Type::Value) # :nodoc:
 
       attr_reader :subtype, :coder
 
-      def initialize(subtype, coder)
+      def initialize(subtype, coder, default: nil)
         @subtype = subtype
         @coder = coder
+        @default = default
         super(subtype)
       end
 
@@ -25,7 +26,7 @@ def deserialize(value)
 
       def serialize(value)
         return if value.nil?
-        unless default_value?(value)
+        unless default_value?(value) && @default.nil?
           super coder.dump(value)
         end
       end

activerecord/test/cases/serialized_attribute_test.rb

@@ -403,6 +403,43 @@ def test_values_cast_from_nil_are_persisted_as_nil
     assert_equal [topic, topic2], Topic.where(content: nil).sort_by(&:id)
   end
 
+  # MySQL doesn't support default values for text columns, so we need to skip this test for MySQL
+  if !current_adapter?(:Mysql2Adapter)
+    def test_serialized_attribute_with_default_can_update_to_default
+      ActiveRecord::Schema.define do
+        create_table :tmp_posts, force: true do |t|
+          t.text     :content, null: false, default: "{}"
+        end
+      end
+      klass = Class.new(ActiveRecord::Base) do
+        self.table_name = "tmp_posts"
+        serialize(:content, Hash)
+      end
+
+      t = klass.create!(content: { "other_key" => "new_value" })
+      assert_equal({ "other_key" => "new_value" }, t.content)
+
+      t.update!(content: {})
+      assert_equal({}, t.content)
+    end
+
+    def test_nil_is_always_persisted_as_default
+      ActiveRecord::Schema.define do
+        create_table :tmp_posts, force: true do |t|
+          t.text     :content, null: false, default: "{}"
+        end
+      end
+      klass = Class.new(ActiveRecord::Base) do
+        self.table_name = "tmp_posts"
+        serialize(:content, Hash)
+      end
+
+      t = klass.create!(content: { foo: "bar" })
+      t.update_attribute :content, nil
+      assert_equal({}, t.content)
+    end
+  end
+
   def test_nil_is_always_persisted_as_null
     Topic.serialize(:content, Hash)