CODEWITHSUNDEEP
google-app-engineapp-engine-ndb
Dylan
Dylan

Reputation: 2684

Query on KeyProperty's parent/ancestor

Is it possible to query based on the ancestors (parent) of a KeyProperty?

EG, something like the following:

class Foo(ndb.Model):
    bar = ndb.KeyProperty()

Foo.query().filter(Foo.bar.parent == some_key)

That is, I want to find all foos which have a bar key where the parent of the bar key is some_key.

I want to avoid having to store the parent of bar as a separate key property if that is possible. Basically I want to do an ancestor query on the KeyProperty, but couldn't see how you could do that, if it was possible at all.

My current solution is to use a ComputedProperty to extract the parent of bar and store it as a separate field. This works, but it seems unnecessary because I'm already storing the parent key as part of the bar key.

Upvotes: 2

Views: 1495

Answers (1)

bossylobster
bossylobster

Reputation: 10163

Yes, this is called an ancestor query:

Foo.query(ancestor=some_key)

UPDATE:

After conversation in the comments, we cleared up the desired result. A query will only work if the property in question is indexed. You could index parents by using a computed property and querying on it's value. Since .parent() will return a key, this should not be an issue:

class Foo(ndb.Model):
  bar = ndb.KeyProperty()
  bar_parent = ndb.ComputedProperty(lambda self: self.bar.parent())

Foo.query(Foo.bar_parent == some_key)

Upvotes: 6

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