How to filter NDB entities having exactly the same repeated properties?

Question

My NDB model class has repeated property:

class Something(ndb.Model):
  tags = ndb.StringProperty(repeated=True)

Is there any way to query for all entities havings tags equal to ['music', 'cinema'] ? Ie each entity returned should have music and cinema tag at the same time and shouldn't have other tags . The GAE doc says that

You cannot compare repeated properties to list objects (the Datastore won't understand it)

Will I have to fetch all entities with one tag and then filter it manually?

Answer 1

Storing a serialized/hashed version of the list and querying for an exact match against that will likely be more efficient than fetching all of your entities:

class Something(ndb.Model):
  tags = ndb.StringProperty(repeated=True)
  tagset = ndb.ComputedProperty(lambda self: ','.join(self.tags.sort()))

Then to query use the same serialization on your search-tags:

    q = Something.query(cls.tagset == ','.join(sorted(['music', 'cinema'])))

Answer 2

Yes, you can use the IN property, which uses a list object when Querying for Repeated Properties :

Something.tags.IN(['music', 'cinema'])

To see if both tags are present, you can use the AND operation:

Something.tags.query(ndb.AND(Something.tags == 'music',
                             Something.tags == 'cinema'))