Under some circumstances an App Engine "get_by_key_name" call using an existing key_name returns None

Question

I've run into a strange problem that I haven't seen before making a get_by_key_name call using the App Engine ORM.

Under no circumstances, one would assume, would the following return None:

Model.get_by_key_name(Model.all().get().key().name())

And yet, that's what I've found that certain key names will do. It's only in a few cases where I'm using Open ID URLs like the following as key_name attributes:

https://me.yahoo.com/a/jadjuh3s0klsghiLhtBNbIiHw8k-#3dcl3

(I've changed a couple of chars to protect the innocent)

Maybe the '#' symbol?

Solution: As Nick Johnson suggested, I needed to modify the query since the entity has a parent:

entity = Model.all().get()
Model.get_by_key_name(entity.key().name(), parent=entity.parent_key())

Whatever the case may be, if there is a circumstance where a key name can't be used to fetch an entity, then it shouldn't be allowed to be used as a key name in the first place.

Answer 1

hi! out of curiosity, do you see this in production, or in the sdk, or both?

i tried to reproduce it with your example key name in http://shell.appspot.com/ , but couldn't:

>>> class Foo(db.Expando):
  pass
>>> Foo(key_name='https://me.yahoo.com/a/jadjuh3s0klsghiLhtBNbIiHw8k-#3dcl3').put()
datastore_types.Key.from_path(u'Foo', u'https://me.yahoo.com/a/jadjuh3s0klsghiLhtBNbIiHw8k-#3dcl3', _app_id_namespace=u'shell')
>>> Foo.get_by_key_name('https://me.yahoo.com/a/jadjuh3s0klsghiLhtBNbIiHw8k-#3dcl3')
<__main__.Foo object at 0x75f9c1aa9181d78>

(granted, i'm not using your model class hierarchy, which you implied might be what's triggering it.)

Answer 2

Model.get_by_key_name(Model.all().get().key().name()) will fail iff the entity returned by the query is a child entity of some other entity. get_by_key_name without a parent parameter looks for an entity with no parents, while the query can return a child entity.

For example:

a = Model1()
a.put()
b = Model2(parent=a)
b.put()
Model2.get_by_key_name(Model2.all().get().key().name()) # Fails to return anything
Model2.get(Model2.all().get().key()) # Works as expected