Question

I have these two models

class Genre( TimeStampAwareModel ):
   genre = models.CharField ( max_length = 255, blank = False )
   parent = models.ForeignKey ( 'self', null=True, blank=True, related_name = "childs" )
   ..
class Track( TimeStampAwareModel ):
   ....
   genre = models.ManyToManyField( Genre )

I have as input list of genres [Pop,Rock,..], since Pop and Rock have child genres too. Now i want to filter all tracks fulfilling following condition

(G1parent OR G1child1 OR G1child2 OR …..) AND (G2parent OR G2child1 OR G2child2 OR …..)

def get_genre_tracks(list_genre):
   ....
   ...
   return tracks

here G1parent is Pop and G2parent is Rock, How can i get this? looking for an elegant solution.

Thanks!

Answer 1

If I understand you properly, you want all tracks that either have a genre of “Rock” or a genre that has “Rock” as a parent. If so:

from django.db.models import Q

Track.objects.filter(Q(genre__genre='Rock') | Q(genre__parent__genre='Rock')).distinct()

EDIT

Actually, after re-reading the question it seems you want what I said, but for a list of genres together, instead of just one at a time. For that, you just need to tweak the above code like:

Track.objects.filter(Q(genre__genre__in=['Rock', 'Pop']) | Q(genre__parent__genre__in=['Rock', 'Pop'])).distinct()

UPDATE

Ah, then it’s a bit more complicated but still doable.

has_rock_genres = Q(genre__genre='Rock') | Q(genre__parent__genre='Rock')
has_pop_genres = Q(genre__genre='Pop') | Q(genre__parent__genre='Pop')

Track.objects.filter(has_rock_genres & has_pop_genres).distinct()

You could do that all in one line, but the code becomes a bit of a mess at that point.

UPDATE

Really giving me a mental workout today, aren’t you? 😉

You’ll need to do something like:

query = None
for genre in genres:
    if query is None:
        query = Q(genre__genre=genre) | Q(genre__parent__genre=genre)
    else:
        query = query & (Q(genre__genre=genre) | Q(genre__parent__genre=genre))

    Track.objects.filter(query).distinct()