Merge pull request #177 from sbook/feature/update_lists

Added the ability to update individual items in ListFields.

Example: 
  
   Message.objects(pk=12).update(set__comments__5__body="Testing 123")

tests/queryset.py

@@ -212,6 +212,55 @@ class QuerySetTest(unittest.TestCase):
 
         Blog.drop_collection()
 
+    def test_update_array_position(self):
+        """Ensure that updating by array position works.
+
+        Check update() and update_one() can take syntax like:
+            set__posts__1__comments__1__name="testc"
+        Check that it only works for ListFields.
+        """
+        class Comment(EmbeddedDocument):
+            name = StringField()
+
+        class Post(EmbeddedDocument):
+            comments = ListField(EmbeddedDocumentField(Comment))
+
+        class Blog(Document):
+            tags = ListField(StringField())
+            posts = ListField(EmbeddedDocumentField(Post))
+
+        Blog.drop_collection()
+
+        comment1 = Comment(name='testa')
+        comment2 = Comment(name='testb')
+        post1 = Post(comments=[comment1, comment2])
+        post2 = Post(comments=[comment2, comment2])
+        blog1 = Blog.objects.create(posts=[post1, post2])
+        blog2 = Blog.objects.create(posts=[post2, post1])
+
+        # Update all of the first comments of second posts of all blogs
+        blog = Blog.objects().update(set__posts__1__comments__0__name="testc")
+        testc_blogs = Blog.objects(posts__1__comments__0__name="testc")
+        self.assertEqual(len(testc_blogs), 2)
+
+        Blog.drop_collection()
+
+        blog1 = Blog.objects.create(posts=[post1, post2])
+        blog2 = Blog.objects.create(posts=[post2, post1])
+
+        # Update only the first blog returned by the query
+        blog = Blog.objects().update_one(
+            set__posts__1__comments__1__name="testc")
+        testc_blogs = Blog.objects(posts__1__comments__1__name="testc")
+        self.assertEqual(len(testc_blogs), 1)
+
+        # Check that using this indexing syntax on a non-list fails
+        def non_list_indexing():
+            Blog.objects().update(set__posts__1__comments__0__name__1="asdf")
+        self.assertRaises(InvalidQueryError, non_list_indexing)
+
+        Blog.drop_collection()
+
     def test_get_or_create(self):
         """Ensure that ``get_or_create`` returns one result or creates a new
         document.