Merge pull request #1946 from erdenezul/refactor_write_concern

Refactor write_concern #1945

Author: erdenezul

mongoengine/document.py

@@ -297,7 +297,7 @@ def modify(self, query=None, **update):
         return True
 
     def save(self, force_insert=False, validate=True, clean=True,
-             write_concern=None, cascade=None, cascade_kwargs=None,
+             write_concern={'w': 1}, cascade=None, cascade_kwargs=None,
              _refs=None, save_condition=None, signal_kwargs=None, **kwargs):
         """Save the :class:`~mongoengine.Document` to the database. If the
         document already exists, it will be updated, otherwise it will be
@@ -359,9 +359,6 @@ def save(self, force_insert=False, validate=True, clean=True,
         if validate:
             self.validate(clean=clean)
 
-        if write_concern is None:
-            write_concern = {'w': 1}
-
         doc = self.to_mongo()
 
         created = ('_id' not in doc or self._created or force_insert)