Django: How to filter Users that belong to a specific group

I'm looking to narrow a query set for a form field that has a foreignkey to the User's table down to the group that a user belongs to.

The groups have been previously associated by me. The model might have something like the following:

myuser = models.ForeignKey(User)

And my ModelForm is very bare bones:

class MyForm(ModelForm):
    class Meta:
        model = MyModel

So when I instantiate the form I do something like this in my views.py:

form = MyForm()

Now my question is, how can I take the myuser field, and filter it so only users of group 'foo' show up.. something like:

form.fields["myuser"].queryset = ???

The query in SQL looks like this:

mysql> SELECT * from auth_user INNER JOIN auth_user_groups ON auth_user.id = auth_user_groups.user_id INNER JOIN auth_group ON auth_group.id = auth_user_groups.group_id WHERE auth_group.name = 'client';

I'd like to avoid using raw SQL though. Is it possible to do so?

Solution

You'll want to use Django's convention for joining across relationships to join to the group table in your query set.

Firstly, I recommend giving your relationship a related_name. This makes the code more readable than what Django generates by default.

class Group(models.Model):
    myuser = models.ForeignKey(User, related_name='groups')

If you want only a single group, you can join across that relationship and compare the name field using either of these methods:

form.fields['myuser'].queryset = User.objects.filter(
    groups__name='foo')
form.fields['myuser'].queryset = User.objects.filter(
    groups__name__in=['foo'])

If you want to qualify multiple groups, use the in clause:

form.fields['myuser'].queryset = User.objects.filter(
    groups__name__in=['foo', 'bar'])

If you want to quickly see the generated SQL, you can do this:

qs = User.objects.filter(groups__name='foo')
print qs.query