Non-root entity group queries returning zero results

Question

I am porting an app from Google App Engine to AppScale, and have discovered peculiar behaviour when performing ancestor queries on entity groups.

If I perform an ancestor query where the parent is not the root, the query returns zero results. If I perform the same query with the parent as root, the correct results are returned.

Easiest to illustrate with an example:

class A(ndb.Model):
  name = ndb.StringProperty()

class B(ndb.Model):
  name = ndb.StringProperty()

class C(ndb.Model):
  name = ndb.StringProperty()
  active = ndb.BooleanProperty()
  sort = ndb.IntegerProperty()

def main():
  a = A(name='I am A')
  a.put()

  b = B(parent=a.key,
        name='I am B')
  b.put()

  C(parent=b.key,
    name='I am C1',
    active=True,
    sort=0).put()

  C(parent=b.key,
    name='I am C2',
    active=True,
    sort=1).put()

  C(parent=b.key,
    name='I am C3',
    active=True,
    sort=2).put()

  query1 = C.query(C.active == True, ancestor=a.key).order(C.sort).fetch(10)
  query2 = C.query(C.active == True, ancestor=b.key).order(C.sort).fetch(10)

  print 'query 1 = %s' % len(query1)
  print 'query 2 = %s' % len(query2)

If I run the above code on App Engine I get 3 results for both queries. If I run it on AppScale, then I only get 3 results for the first query, and 0 results for the second query.

AppScale uses Cassandra as the datastore. Is this a subtle difference in behaviour between the App Engine datastore and Cassandra?

Answer 1

This is a bug in AppScale where we used the full path of the provided ancestor and not just its root entity for composite queries. The fix for it can be found here: https://github.com/AppScale/appscale/pull/1633