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.
• Users have many Roles, and Roles many Users. (ManyToMany)
• Events have many Users, and Users many Events. (ManyToMany)
• But for any given Event, any User may have only one Role.

How can this be represented in the model?

Answer 1

zacherates writes:

I’d model Role as an association class between Users and Roles (…)

I’d also reccomed this solution, but you can also make use of some syntactical sugar provided by Django: ManyToMany relation with extra fields.

Example:

class User(models.Model):     name = models.CharField(max_length=128)  class Event(models.Model):     name = models.CharField(max_length=128)     members = models.ManyToManyField(User, through='Role')      def __unicode__(self):         return self.name  class Role(models.Model):     person = models.ForeignKey(User)     group = models.ForeignKey(Event)     date_joined = models.DateField()     invite_reason = models.CharField(max_length=64)