Model not updating after `put` if Query is used

[maininformer]

Hello again, I found what seems to be a bug, here is a test:

from google.cloud import ndb

class Profile(ndb.Model):
    name = ndb.TextProperty()
    book = ndb.TextProperty()

class SomeKind:
    def __init__(self, profile):
        self.profile = profile

def init():
    profile = Profile(name='Annaka Harris')
    profile.put()
    return profile.key, SomeKind(profile)

if __name__ == '__main__':
    with ndb.Client().context():
        key, somek = init()

        # Different behavior based on how we query
        # ours = Profile.get_by_id(key.id())
        # ours = key.get()
        ours = [x for x in ndb.Query(kind='Profile').fetch() if x.key == key][0]

        ours.book = 'Conscious'
        print('putting: ', ours)
        ours.put()

        print('getting: ', somek.profile)
        assert somek.profile.book == 'Conscious'

Notes: basically, if we get the model using either get_by_id or key.get(), then the entity on SomeKind will also update; however, if I use ndb.Query, it will not. Previously all worked. You may uncomment different approaches to compare.

[cguardia]

@plumSemPy Hello and thanks for your reports. This is not really a problem with put(). The problem comes when assigning the new value to book. What happens is that, by default, key.get() uses the context cache to get the entity, so it gets the same SomeKind instance defined above. You can see that right after the ours = assignment in the commented out lines, ours is actually the same object as somek, and thus gets updated.

However, the fetch call from our _datastore_query module does not use the cache. It creates a new entity, which means when the assignment is done, it is not dealing with the same instance anymore. If you set the cache policy of the context to False (cache_policy=False), the commented out lines will fail the assertion as well, since now the model instance will be the one returned by the datastore call.

Let me see if we can use the cache in the fetch call as well, to get the same behavior.

[maininformer]

Interesting, thank you for explaining.

[cguardia]

@plumSemPy with the fix from #454, all three lines above will work, but beware: if caching is turned off, none of them will work.

[maininformer]

Thank you 🙏