Fixes bug using positional operator to update embedded documents.

append_field wasn't getting reset to True in the loop, so fields wouldn't
get appended to clean_fields after str was encountered

[#354]

AUTHORS

@@ -73,4 +73,5 @@ that much better:
  * Julien Rebetez
  * Marc Tamlyn
  * Karim Allah
+ * Adam Parrish
 

docs/changelog.rst

@@ -5,6 +5,7 @@ Changelog
 Changes in dev
 ==============
 
+- Fixed positional operator when replacing embedded documents
 - Added Non-Django Style choices back (you can have either)
 - Fixed __repr__ of a sliced queryset
 - Added recursive validation error of documents / complex fields

mongoengine/queryset.py

@@ -1276,8 +1276,8 @@ class QuerySet(object):
                 parts = []
 
                 cleaned_fields = []
-                append_field = True
                 for field in fields:
+                    append_field = True
                     if isinstance(field, str):
                         # Convert the S operator to $
                         if field == 'S':

tests/queryset.py

@@ -378,6 +378,34 @@ class QuerySetTest(unittest.TestCase):
         self.assertRaises(OperationError, update_nested)
         Simple.drop_collection()
 
+    def test_update_using_positional_operator_embedded_document(self):
+        """Ensure that the embedded documents can be updated using the positional
+        operator."""
+
+        class Vote(EmbeddedDocument):
+            score = IntField()
+
+        class Comment(EmbeddedDocument):
+            by = StringField()
+            votes = EmbeddedDocumentField(Vote)
+
+        class BlogPost(Document):
+            title = StringField()
+            comments = ListField(EmbeddedDocumentField(Comment))
+
+        BlogPost.drop_collection()
+
+        c1 = Comment(by="joe", votes=Vote(score=3))
+        c2 = Comment(by="jane", votes=Vote(score=7))
+
+        BlogPost(title="ABC", comments=[c1, c2]).save()
+
+        BlogPost.objects(comments__by="joe").update(set__comments__S__votes=Vote(score=4))
+
+        post = BlogPost.objects.first()
+        self.assertEquals(post.comments[0].by, 'joe')
+        self.assertEquals(post.comments[0].votes.score, 4)
+
     def test_mapfield_update(self):
         """Ensure that the MapField can be updated."""
         class Member(EmbeddedDocument):