New records should remain new after yaml serialization

activerecord/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   New records remain new after YAML serialization.
+
+    *Sean Griffin*
+
 *   PostgreSQL support default values for enum types. Fixes #7814.
 
     *Yves Senn*

activerecord/lib/active_record/core.rb

@@ -284,7 +284,7 @@ module ActiveRecord
 
       init_internals
 
-      @new_record = false
+      @new_record = coder['new_record']
 
       self.class.define_attribute_methods
 
@@ -354,6 +354,7 @@ module ActiveRecord
     #   coder # => {"attributes" => {"id" => nil, ... }}
     def encode_with(coder)
       coder['attributes'] = @raw_attributes
+      coder['new_record'] = new_record?
     end
 
     # Returns true if +comparison_object+ is the same exact object, or +comparison_object+

activerecord/lib/active_record/persistence.rb

@@ -49,7 +49,11 @@ module ActiveRecord
       def instantiate(attributes, column_types = {})
         klass = discriminate_class_for_record(attributes)
         column_types = klass.decorate_columns(column_types.dup)
-        klass.allocate.init_with('attributes' => attributes, 'column_types' => column_types)
+        klass.allocate.init_with(
+          'attributes' => attributes,
+          'column_types' => column_types,
+          'new_record' => false,
+        )
       end
 
       private

activerecord/test/cases/yaml_serialization_test.rb

@@ -52,4 +52,21 @@ class YamlSerializationTest < ActiveRecord::TestCase
     assert_equal 123, topic.parent_id
     assert_equal 123, YAML.load(YAML.dump(topic)).parent_id
   end
+
+  def test_new_records_remain_new_after_round_trip
+    topic = Topic.new
+
+    assert topic.new_record?, "Sanity check that new records are new"
+    assert YAML.load(YAML.dump(topic)).new_record?, "Record should be new after deserialization"
+
+    topic.save!
+
+    assert_not topic.new_record?, "Saved records are not new"
+    assert_not YAML.load(YAML.dump(topic)).new_record?, "Saved record should not be new after deserialization"
+
+    topic = Topic.select('title').last
+
+    assert_not topic.new_record?, "Loaded records without ID are not new"
+    assert_not YAML.load(YAML.dump(topic)).new_record?, "Record should not be new after deserialization"
+  end
 end