models.py

from django.db import models
from django.contrib.auth.models import User
import logging


class Role(models.Model):
    name = models.CharField(max_length=30, null=False, blank=False)
    users = models.ManyToManyField(User, related_name="roles")
    course_id = models.CharField(max_length=255, blank=True, db_index=True)

    def __unicode__(self):
        return self.name + " for " + (self.course_id if self.course_id else "all courses")

    def inherit_permissions(self, role): # TODO the name of this method is a little bit confusing,
                                         # since it's one-off and doesn't handle inheritance later
        if role.course_id and role.course_id != self.course_id:
            logging.warning("%s cannot inheret permissions from %s due to course_id inconsistency" % 
                            (self, role))
        for per in role.permissions.all():
            self.add_permission(per)

    def add_permission(self, permission):
        self.permissions.add(Permission.objects.get_or_create(name=permission)[0])

    def has_permission(self, permission):
        return self.permissions.filter(name=permission).exists()


class Permission(models.Model):
    name = models.CharField(max_length=30, null=False, blank=False, primary_key=True)
    roles = models.ManyToManyField(Role, related_name="permissions")

    def __unicode__(self):
        return self.name