Question

New to Django, third question on it today…

I have the following (simplified) models defined:

class Band(models.Model):
    bandname = models.CharField('Band name', max_length=300)

class Release(models.Model):
    title = models.CharField(max_length=300)
    artist = models.ManyToManyField('Band')
    formats = models.ManyToManyField('Format')

class Format(models.Model):
    kind = models.CharField(max_length=300)

class Song(models.Model):
    title = models.CharField(max_length=500)
    release = models.ForeignKey('Release')

(I’ve removed extra fields for the sake of readability)

Now, when I try to run the following query, it adds hundreds of extra queries to the page:

s = Song.objects.all() # adds 367 queries

I’ve tried changing it to this:

s = Song.objects.select_related('band', 'release').all() # adds 245 queries

This still sucks and I don’t know what else I can do. There are 122 songs in my database, on 52 releases, by 39 bands. Not sure if this helps but I’m at a loss.

Any tips on how to optimise this? I need to be able to show the band and release name for each Song. A Release is ManyToMany for Band because some of them are split releases by multiple artists.

thanks,
Matt

Answer 1

Django select_related does not follow many-to-many relationships, and I’m guessing that is what is causing the large query count.

My suggestion is to use values(), and double__underscore__notation to get the required values. Something similar to this should work on django 1.3 and above:

s = Song.objects.values('title', 'release__title', 'release__artist__bandname')