CODEWITHSUNDEEP
pythongoogle-app-enginegoogle-cloud-datastoreapp-engine-ndb
phoebus
phoebus

Reputation: 21

Appengine datastore, polymodel, and projection

I have a polymodel for all contacts

from google.appengine.ext import ndb
from google.appengine.ext.ndb import polymodel

class Contact(polymodel.PolyModel):
    telephone = ndb.StructuredProperty(Telephone, repeated=True)
    email = ndb.StructuredProperty(Email, repeated=True)

The Telephone and Email model classes have two simple StringProperty properties: type and value.

I have a model Person who uses this polymodel:

class Person(Contact):
    name = ndb.StringProperty()

I would like to use projection to reduce the amount of output. So when I query a property of the parent (i.e. polymodel), such as:

qry = Person.query(projection=['telephone.value'])

everything works. But if I query a property of the Person class, (either of)

qry = Person.query(projection=['name'])
qry = Person.query(projection=[Person.name])

I receive an InvalidPropertyError: Unknown property name exception.

Is this a bug of ndb to look into the kind and not the actual class?

Please let me know if there is a way around it (of course one is to not use polymodels). Thanks.

EDIT:

Below I present a simpler model (removed StructuredProperty) which gives the same issue:

class Contact(polymodel.PolyModel):
    telephone = ndb.StringProperty()

class Person(Contact):
    name = ndb.StringProperty()

This works:

qry = Person.query(projection=['telephone'])

This does not work:

qry = Person.query(projection=['name'])

Upvotes: 0

Views: 276

Answers (1)

Tim Hoffman
Tim Hoffman

Reputation: 12986

There are a lot of problems trying to combine StructuredProperty with PolyModel - see ndb.StructuredProperty not calling ndb.PolyModel subclass methods and AppEngine NDB PolyModel getting properties for instance.

Basically the design of PolyModel and StructuredProperty tend to preclude their combined use.

I know you question is about projection queries but the fundamental problems here will no doubt get in the way of the projection query working.

Upvotes: 1

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