Test checking can save if not included

ref: MongoEngine/mongoengine#70

mongoengine/fields.py

@@ -393,6 +393,8 @@ class ComplexDateTimeField(StringField):
         data = super(ComplexDateTimeField, self).__get__(instance, owner)
         if data == None:
             return datetime.datetime.now()
+        if isinstance(data, datetime.datetime):
+            return data
         return self._convert_from_string(data)
 
     def __set__(self, instance, value):

tests/test_document.py

@@ -1640,6 +1640,52 @@ class DocumentTest(unittest.TestCase):
         self.assertEqual(person.name, None)
         self.assertEqual(person.age, None)
 
+    def test_can_save_if_not_included(self):
+
+        class EmbeddedDoc(EmbeddedDocument):
+            pass
+
+        class Simple(Document):
+            pass
+
+        class Doc(Document):
+            string_field = StringField(default='1')
+            int_field = IntField(default=1)
+            float_field = FloatField(default=1.1)
+            boolean_field = BooleanField(default=True)
+            datetime_field = DateTimeField(default=datetime.datetime.now)
+            embedded_document_field = EmbeddedDocumentField(EmbeddedDoc, default=lambda: EmbeddedDoc())
+            list_field = ListField(default=lambda: [1, 2, 3])
+            dict_field = DictField(default=lambda: {"hello": "world"})
+            objectid_field = ObjectIdField(default=ObjectId)
+            reference_field = ReferenceField(Simple, default=lambda: Simple().save())
+            map_field = MapField(IntField(), default=lambda: {"simple": 1})
+            decimal_field = DecimalField(default=1.0)
+            complex_datetime_field = ComplexDateTimeField(default=datetime.datetime.now)
+            url_field = URLField(default="http://mongoengine.org")
+            dynamic_field = DynamicField(default=1)
+            generic_reference_field = GenericReferenceField(default=lambda: Simple().save())
+            sorted_list_field = SortedListField(IntField(), default=lambda: [1, 2, 3])
+            email_field = EmailField(default="ross@example.com")
+            geo_point_field = GeoPointField(default=lambda: [1, 2])
+            sequence_field = SequenceField()
+            uuid_field = UUIDField(default=uuid.uuid4)
+            generic_embedded_document_field = GenericEmbeddedDocumentField(default=lambda: EmbeddedDoc())
+
+
+        Simple.drop_collection()
+        Doc.drop_collection()
+
+        Doc().save()
+
+        my_doc = Doc.objects.only("string_field").first()
+        my_doc.string_field = "string"
+        my_doc.save()
+
+        my_doc = Doc.objects.get(string_field="string")
+        self.assertEqual(my_doc.string_field, "string")
+        self.assertEqual(my_doc.int_field, 1)
+
     def test_document_update(self):
 
         def update_not_saved_raises():