How to create a triple-join table with Django

Question

Using Django\'s built in models, how would one create a triple-join between three models.

For example:

• Users, Roles, and Events are the models.
• Us

Answer 1

I'd recommend just creating an entirely separate model for this.

class Assignment(Model):
    user = ForeignKey(User)
    role = ForeignKey(Role)
    event = ForeignKey(Event)

This lets you do all the usual model stuff, such as

user.assignment_set.filter(role__name="Chaperon")
role.assignment_set.filter(event__name="Silly Walkathon")

The only thing left is to enforce your one-role-per-user-per-event restriction. You can do this in the Assignment class by either overriding the save method (http://docs.djangoproject.com/en/dev/topics/db/models/#overriding-predefined-model-methods) or using signals (http://docs.djangoproject.com/en/dev/topics/signals/)