Django ManyToMany filter()

Django ManyToMany filter()

I have a model:
class Zone(models.Model):
    name = models.CharField(max_length=128)
    users = models.ManyToManyField(User, related_name='zones', null=True, blank=True)

And I need to contruct a filter along the lines of:
u = User.objects.filter(...zones contains a particular zone...)

It has to be a filter on User and it has to be a single filter parameter. The reason for this is that I am constructing a URL querystring to filter the admin user changelist: http://myserver/admin/auth/user/?zones=3
It seems like it should be simple but my brain isn't cooperating!

Solutions/Answers:

Answer 1:

Just restating what Tomasz said.

There are many examples of FOO__in=... style filters in the many-to-many and many-to-one tests. Here is syntax for your specific problem:

users_in_1zone = User.objects.filter(zones__id=<id1>)
# same thing but using in
users_in_1zone = User.objects.filter(zones__in=[<id1>])

# filtering on a few zones, by id
users_in_zones = User.objects.filter(zones__in=[<id1>, <id2>, <id3>])
# and by zone object (object gets converted to pk under the covers)
users_in_zones = User.objects.filter(zones__in=[zone1, zone2, zone3])

The double underscore (__) syntax is used all over the place when working with querysets.

Answer 2:

Note that if the user may be in multiple zones used in the query, you may probably want to add .distinct(). Otherwise you get one user multiple times:

users_in_zones = User.objects.filter(zones__in=[zone1, zone2, zone3]).distinct()

References