Google App Engine ndb performance on repeated property

Question

Do I pay a penalty on query performance if I choose to query repeated property? For example:

class User(ndb.Model):
    user_name = ndb.StringProperty()
    login_providers = ndb.KeyProperty(repeated=true)

fbkey = ndb.Key("ProviderId", 1, "ProviderName", "FB")
for entry in User.query(User.login_providers == fbkey):
    # Do something with entry.key

vs

class User(ndb.Model)
    user_name = ndb.StringProperty()

class UserProvider(ndb.Model):
    user_key = ndb.KeyProperty(kind=User)
    login_provider = ndb.KeyProperty()

for entry in UserProvider.query(
    UserProvider.user_key == auserkey,
    UserProvider.login_provider == fbkey
):
    # Do something with entry.user_key

Based on the documentation from GAE, it seems that Datastore take care of indexing and the first less verbose option would be using the index. However, I failed to find any documentation to confirm this.

Edit

The sole purpose of UserProvider in the second example is to create a one-to-many relationship between a user and it's login_provider. I wanted to understand if it worth the trouble of creating a second entity instead of querying on repeated property. Also, assume that all I need is the key from the User.

It's unclear whether you also have a UserProvider class in the first version, or whether you just create Keys pointing nowhere (which is permissible, BTW :-). The two queries are not equivalent since one returns User entities and the other UserProvider entities. — Guido van Rossum
@GuidovanRossum I updated the question and hopefully is clearer now. It did take me a while to understand what is a ndb.Key, given that you can create a Key that points to nothing. — marcoseu

dragonx dragonx · Accepted Answer · 2013-07-03T17:16:53

No. But you'll raise your write costs because each entry needs to be indexed, and write costs are based on the number of indexes updated.

Google App Engine ndb performance on repeated property

1 Answers