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Editorial Team
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Asked: 2026-06-04T07:08:59+00:00

Let’s say I have: class Like(db.Model): user = db.ReferenceProperty(User,collection_name=’likes’) photo = db.ReferenceProperty(Photo,collection_name=’likes_received’) created =

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Let’s say I have:

class Like(db.Model):
    user = db.ReferenceProperty(User,collection_name='likes')
    photo = db.ReferenceProperty(Photo,collection_name='likes_received')
    created = db.DateTimeProperty(auto_now_add=True)

Is it possible to run a projection query that returns only a list of photo keys?

photos = db.GqlQuery("SELECT photo FROM Like WHERE created < DATETIME(2013, 1, 1, 0, 0, 0)").fetch(10)

The code above produces:

BadValueError: Unsupported data type (<class 'models.Photo'>)
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1 Answer

  1. Editorial Team

    I apologize, my first answer was wrong. There is a real problem with projection queries — ReferenceProperty is not (yet) supported. Alfred is looking into this; since the 1.6.6 prerelease SDK went out today and this was already present in the 1.6.5 SDk I doubt we’ll get this fixed in 1.6.6 but 1.6.7 is a possibility.

    As workarounds, you could use db.ListProperty(db.Key), which is a list of keys (you’d store only one key), or a StringProperty whose value is the str() of the key.

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