GAE python ndb put_async issue

Question

I've a model named Conversation with some fields that includes date_created and date_updated as DateTimePropterty with auto_now_add and auto_now.

If I update the model using put() method, date_updated field is getting updated. But when I use the put_async method, the value in the date_updated field is not updating.

And I also have the test case using Python's unittest.Testcase, there it works fine.

Note: It works when I use put_async().get_result().

Sample model class:

class Conversation(ndb.Model):

   participants = ndb.StringProperty(repeated=True)  
   conversation_name = ndb.StringProperty()
   date_created = ndb.DateTimeProperty(required=True, auto_now_add=True)
   date_updated = ndb.DateTimeProperty(required=True, auto_now=True)

   @staticmethod
   def update_conversation_date_by_id(conversation_id):
       conversation = Conversation.get_by_id(conversation_id) if conversation_id else None
       if conversation is None:
           raise CannotFindEntity("Given conversation_id is not found")
       else:
           conversation.put_async().get
       return conversation

possible duplicate of Is ndb async guaranteed to execute after application request has finished? — Ryne Everett

Paul Collingwood Paul Collingwood · Accepted Answer · 2014-04-29T11:14:41

If the request handler exits before the NDB put finishes the put might never happen.

class MyRequestHandler(webapp2.RequestHandler):
  def get(self):
    acct = Account.get_by_id(users.get_current_user().user_id())
    acct.view_counter += 1
    future = acct.put_async()
    # ...read something else from Datastore...
    template.render(...)
    future.get_result()

Try adding something like the last line in that codeblock to force it to wait.

In this example, it's a little silly to call future.get_result: the application never uses the result from NDB. That code is just in there to make sure that the request handler doesn't exit before the NDB put finishes; if the request handler exits too early, the put might never happen. As a convenience, you can decorate the request handler with @ndb.toplevel. This tells the handler not to exit until its asynchronous requests have finished. This in turn lets you send off the request and not worry about the result.

https://developers.google.com/appengine/docs/python/ndb/async

GAE python ndb put_async issue

2 Answers