Implementing DateTimePropery._db_(set|get)_value.

ndb/src/google/cloud/ndb/model.py

@@ -2284,6 +2284,22 @@ def _prepare_for_put(self, entity):
             value = self._now()
             self._store_value(entity, value)
 
+    def _db_set_value(self, v, p, value):
+        """Helper for :meth:`_serialize`.
+
+        Raises:
+            NotImplementedError: Always. This method is virtual.
+        """
+        raise NotImplementedError
+
+    def _db_get_value(self, v, unused_p):
+        """Helper for :meth:`_deserialize`.
+
+        Raises:
+            NotImplementedError: Always. This method is virtual.
+        """
+        raise NotImplementedError
+
 
 class DateProperty(DateTimeProperty):
     __slots__ = ()

ndb/tests/unit/test_model.py

@@ -1837,6 +1837,18 @@ def test__prepare_for_put_auto_now_add():
                 assert entity._values == {prop._name: _now.return_value}
                 _now.assert_called_once_with()
 
+    @staticmethod
+    def test__db_set_value():
+        prop = model.DateTimeProperty(name="dt_val")
+        with pytest.raises(NotImplementedError):
+            prop._db_set_value(None, None, None)
+
+    @staticmethod
+    def test__db_get_value():
+        prop = model.DateTimeProperty(name="dt_val")
+        with pytest.raises(NotImplementedError):
+            prop._db_get_value(None, None)
+
 
 class TestDateProperty:
     @staticmethod