Cloud Datastore: ways to avoid race conditions

Question

I have lots of views manipulating entities of same kind:

def view1(request, key):
    user = ndb.Key(urlsafe=key).get()
    user.x = 1
    user.put()
    ...

de         


        

Answer 1

Wrap your get and put into a transaction. This will ensure you cannot stomp over a different update.

You can read more about transactions with the NDB Client Library documentation.

In your code, you could for example just use the NDB transaction decorator:

@ndb.transactional(retries=1)
def view1(request, key):
    user = ndb.Key(urlsafe=key).get()
    user.x = 1
    user.put()
    ...

@ndb.transactional(retries=1)    
def view2(request, key):
    user = ndb.Key(urlsafe=key).get()
    user.y = 2
    user.put()