Updates with no operator should default to $set Fix #667

docs/guide/querying.rst

@@ -525,6 +525,13 @@ modifier comes before the field, not after it::
     >>> post.tags
     ['database', 'nosql']
 
+.. note::
+
+    If no modifier operator is specified the default will be `set` the both following sentences are identical::
+
+        >>> BlogPost.objects(id=post.id).update(title='Example Post')
+        >>> BlogPost.objects(id=post.id).update(set__title='Example Post')
+
 .. note::
 
     In version 0.5 the :meth:`~mongoengine.Document.save` runs atomic updates

mongoengine/queryset/transform.py

@@ -164,6 +164,9 @@ def update(_doc_cls=None, **update):
             mongo_update.update(value)
             continue
         parts = key.split('__')
+        # if there is no operator, default to "set"
+        if len(parts) < 3 and parts[0] not in UPDATE_OPERATORS:
+            parts.insert(0, 'set')
         # Check for an operator and transform to mongo-style if there is
         op = None
         if parts[0] in UPDATE_OPERATORS:

tests/document/instance.py

@@ -1074,11 +1074,13 @@ class InstanceTest(unittest.TestCase):
 
         self.assertRaises(OperationError, update_no_value_raises)
 
-        def update_no_op_raises():
+        def update_no_op_should_default_to_set():
             person = self.Person.objects.first()
             person.update(name="Dan")
+            person.reload()
+            return person.name
 
-        self.assertRaises(InvalidQueryError, update_no_op_raises)
+        self.assertEqual("Dan", update_no_op_should_default_to_set())
 
     def test_update_unique_field(self):
         class Doc(Document):