Fixed as_pymongo to return the id (#386)

docs/changelog.rst

@@ -4,6 +4,7 @@ Changelog
 
 Changes in 0.8.3
 ================
+- Fixed as_pymongo to return the id (#386)
 - Document.select_related() now respects `db_alias` (#377)
 - Reload uses shard_key if applicable (#384)
 - Dynamic fields are ordered based on creation and stored in _fields_ordered (#396)

mongoengine/queryset/queryset.py

@@ -1423,7 +1423,8 @@ class QuerySet(object):
         # used. If not, handle all fields.
         if not getattr(self, '__as_pymongo_fields', None):
             self.__as_pymongo_fields = []
-            for field in self._loaded_fields.fields - set(['_cls', '_id']):
+
+            for field in self._loaded_fields.fields - set(['_cls']):
                 self.__as_pymongo_fields.append(field)
                 while '.' in field:
                     field, _ = field.rsplit('.', 1)

tests/queryset/queryset.py

@@ -3227,6 +3227,9 @@ class QuerySetTest(unittest.TestCase):
         User(name="Bob Dole", age=89, price=Decimal('1.11')).save()
         User(name="Barack Obama", age=51, price=Decimal('2.22')).save()
 
+        results = User.objects.only('id', 'name').as_pymongo()
+        self.assertEqual(results[0].keys(), ['_id', 'name'])
+
         users = User.objects.only('name', 'price').as_pymongo()
         results = list(users)
         self.assertTrue(isinstance(results[0], dict))