Filter on a list of tags

I'm trying to开发者_如何学编程 select all the songs in my Django database whose tag is any of those in a given list. There is a Song model, a Tag model, and a SongTag model (for the many to many relationship).

This is my attempt:

taglist = ["cool", "great"]
tags = Tag.objects.filter(name__in=taglist).values_list('id', flat=True)
song_tags = SongTag.objects.filter(tag__in=list(tags))

At this point I'm getting an error:

DatabaseError: MultiQuery does not support keys_only.

What am I getting wrong? If you can suggest a completely different approach to the problem, it would be more than welcome too!

EDIT: I should have mentioned I'm using Django on Google AppEngine with django-nonrel

You shouldn't use m2m relationship with AppEngine. NoSQL databases (and BigTable is one of them) generally don't support JOINs, and programmer is supposed to denormalize the data structure. This is a deliberate design desicion: while your database will contain redundant data, your read queries will be much simpler (no need to combine data from 3 tables), which in turn makes the design of DB server much simpler as well (of course this is made for the sake of optimization and scaling)

In your case you should probably get rid of Tag and SongTag models, and just store the tag in the Song model as a string. I of course assume that Tag model only contains id and name, if Tag in fact contains more data, you should still have Tag model. Song model in that case should contain both tag_id and tag_name. The idea, as I explained above, is to introduce redundancy for the sake of simpler queries

Please, please let the ORM build the query for you:

song_tags = SongTag.objects.filter(tag__name__in = taglist)

You should try to use only one query, so that Django also generates only one query using a join. Something like this should work:

Song.objects.filter(tags__name__in=taglist)

You may need to change some names from this example (most likely the tags in tags__name__in), see https://docs.djangoproject.com/en/1.3/ref/models/relations/.