Django : select_related with ManyToManyField
Solution 1
Django versions 1.4 and above have prefetch_related
for this purpose.
The prefetch_related
method is similar to select_related
, but does not do a database join. Instead, it executes additional database queries and does the joining in Python.
Solution 2
If you're not on Django 1.4, there's also the django-batch-select library, which works basically the same way as prefetch_related.
Paul Tarjan
I'm a Distinguished Engineer at Robinhood. I used to be the Tech Lead of Developer Productivity at Stripe where I built Sorbet. Before that I was the CTO and cofounder at Trimian. Before that I was a Software Engineer at Facebook on HHVM and the Open Graph. Before that I was the Tech Lead for Yahoo! SearchMonkey. See my homepage for more.
Updated on February 27, 2020Comments
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Paul Tarjan over 4 years
I have :
class Award(models.Model) : name = models.CharField(max_length=100, db_index=True) class Alias(models.Model) : awards = models.ManyToManyField('Award', through='Achiever') class Achiever(models.Model): award = models.ForeignKey(Award) alias = models.ForeignKey(Alias) count = models.IntegerField(default=1)
How can I have an
Alias
which has all itsachiever_set
andawards
prepopulated?>>> db.reset_queries() >>> Alias.objects.filter(id="450867").select_related("achiever_set__award").get().achiever_set.all()[0].award.name u'Perma-Peddle' >>> len(db.connection.queries) 3 >>> db.reset_queries() >>> Alias.objects.filter(id="450867").select_related("awards").get().awards.all()[0].name u'Dwarfageddon (10 player)' >>> len(db.connection.queries) 2
I'm going to need a lot of access to the award that an alias has already gotten (both the intermediate table and the awards themselves). How can I batch all of these?