fix quoting in order_by, add get_or_none

tests/test_many_to_many.py

@@ -83,6 +83,18 @@ async def test_not_saved_raises_error(cleanup):
             await post.categories.add(news)
 
 
+@pytest.mark.asyncio
+async def test_not_existing_raises_error(cleanup):
+    async with database:
+        guido = await Author(first_name="Guido", last_name="Van Rossum").save()
+        post = await Post.objects.create(title="Hello, M2M", author=guido)
+
+        with pytest.raises(NoMatch):
+            await post.categories.get()
+
+        assert await post.categories.get_or_none() is None
+
+
 @pytest.mark.asyncio
 async def test_assigning_related_objects(cleanup):
     async with database:
@@ -95,6 +107,9 @@ async def test_assigning_related_objects(cleanup):
         # or from the other end:
         await news.posts.add(post)
 
+        assert await post.categories.get_or_none(name="no exist") is None
+        assert await post.categories.get_or_none(name="News") == news
+
         # Creating columns object from instance:
         await post.categories.create(name="Tips")
         assert len(post.categories) == 2