NDB using Users API to form an entity group

Question

I'm trying to wrap my head around what seems to be a very simple use case, but I seem to be failing miserably. The goal of the exercise is to look up a set of records for the user that logs in using the Google Accounts username within the high replication datastore and be extremely consistent.

My data looks like this:

class Account(ndb.Model):
    owner = ndb.UserProperty()
    name = ndb.StringProperty()

class Content(ndb.Model):
    content = ndb.StringProperty()

When I first create the account, I just do the following:

current_user = users.get_current_user()
new_account = Account(owner=current_user, name='Some Name')
new_account.put()

Now create content:

new_content = Content(parent=new_account.key, content='Some Content')
new_content.put()

When the user logs in, I can only query by UserProperty, but I seem to be unable to set user as the parent for an entity group, so how do I make sure that I always can look-up the Account by the logged in user and be extremely consistent?

Once I have the account, the ancestor query process will ensure consistency for content retrieval, but I'm stuck on figuring out ancestry based on User.

To expand a bit on what Nick suggested, I'm actually going forward with a mapping entity that will map the user ID to an account key. This way I can have many users for an account, but still use the get() to retrieve the account. — Sologoub, Apr 24 '12 at 17:19
The docs also advise not storing a UserProperty, as it can become inconsistent if the user changes their email address: https://developers.google.com/appengine/docs/python/users/userobjects — Spycho, Aug 24 '13 at 10:41

score 5 · Accepted Answer · answered Apr 23 '12 at 02:40

5

The easiest and best way to do this is using key names. In this case, the key name for your Account entity should be the ID of the user. You can create accounts like this:

new_account = Account(owner=current_user, id=current_user.user_id(), name='Some Name')

And you can look them up like this:

existing_account = Account.get_by_id(current_user.user_id())

answered Apr 23 '12 at 02:40

Nick Johnson

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Thanks, Nick! That's exactly what I was looking for. Guess I missed it in the docs. – Sologoub Apr 23 '12 at 04:02

score 0 · Answer 2 · answered Apr 23 '12 at 00:20

0

I'm not sure why exactly you want to do that, but you have to create a parent entity for Account as well, so that you can perform queries on it with an ancestor.

answered Apr 23 '12 at 00:20

Albert

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Oh gosh. I thought he wanted to created multiple Account entities per user. If you just want to ensure consistency when querying for Account entities, then @NickJohnson's answer is the way to go. :) – Albert Apr 23 '12 at 03:01

NDB using Users API to form an entity group

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