Django: Order a model by a many-to-many field

Question

I am writing a Django application that has a model for People, and I have hit a snag. I am assigning Role objects to people using a Many-To-Many relationship - where Roles have

Answer 1

Here's a way to do it without an annotation:

class Role(models.Model):
    pass

class PersonRole(models.Model):
    weight = models.IntegerField()
    person = models.ForeignKey('Person')
    role = models.ForeignKey(Role)

    class Meta:
        # if you have an inline configured in the admin, this will 
        # make the roles order properly 
        ordering = ['weight'] 

class Person(models.Model):
    roles = models.ManyToManyField('Role', through='PersonRole')

    def ordered_roles(self):
        "Return a properly ordered set of roles"
        return self.roles.all().order_by('personrole__weight')

This lets you say something like:

>>> person = Person.objects.get(id=1)
>>> roles = person.ordered_roles()