jacobian · February 15, 2011 18:11 · Feb 15, 2011
diff --git a/models.py b/models.py
@@ -0,0 +1,28 @@
+from django.db import models
+
+class Person(models.Model):
+    name = models.CharField(max_length=200)
+    groups = models.ManyToManyField('Group', through='GroupMember', related_name='people')
+
+    class Meta:
+        ordering = ['name']
+
+    def __unicode__(self):
+        return self.name
+
+class Group(models.Model):
+    name = models.CharField(max_length=200)
+
+    class Meta:
+        ordering = ['name']
+
+    def __unicode__(self):
+        return self.name
+
+class GroupMember(models.Model):
+    person = models.ForeignKey(Person, related_name='membership')
+    group = models.ForeignKey(Group, related_name='membership')
+    type = models.CharField(max_length=100)
+
+    def __unicode__(self):
+        return "%s is in group %s (as %s)" % (self.person, self.group, self.type)
diff --git a/tests.py b/tests.py
@@ -0,0 +1,44 @@
+from django.test import TestCase
+from .models import Person, Group, GroupMember
+
+class M2MThroughTest(TestCase):
+
+    def setUp(self):
+        # Create three people:
+        self.joe = Person.objects.create(name='Joe')
+        self.jim = Person.objects.create(name='Jim')
+        self.bob = Person.objects.create(name='Bob')
+
+        # And three groups:
+        self.jocks = Group.objects.create(name='Jocks')
+        self.nerds = Group.objects.create(name='Nerds')
+        self.skaters = Group.objects.create(name='Skaters')
+
+        # Every person is a member of every group, but
+        # Joe admins jocks, Jim admins nerds, and Bob admins skaters.
+        GroupMember.objects.create(person=self.joe, group=self.jocks, type="admin")
+        GroupMember.objects.create(person=self.jim, group=self.jocks, type="member")
+        GroupMember.objects.create(person=self.bob, group=self.jocks, type="member")
+
+        GroupMember.objects.create(person=self.joe, group=self.nerds, type="member")
+        GroupMember.objects.create(person=self.jim, group=self.nerds, type="admin")
+        GroupMember.objects.create(person=self.bob, group=self.nerds, type="member")
+
+        GroupMember.objects.create(person=self.joe, group=self.skaters, type="member")
+        GroupMember.objects.create(person=self.jim, group=self.skaters, type="member")
+        GroupMember.objects.create(person=self.bob, group=self.skaters, type="admin")
+
+    def test_unfiltered_membership(self):
+        # Which groups is Jim in?
+        jims_groups = Group.objects.filter(people=self.jim)
+        self.assertEqual(list(jims_groups), [self.jocks, self.nerds, self.skaters])
+
+    def test_admin_groups(self):
+        # But which groups does Jim admin?
+        jim_admins = Group.objects.filter(people=self.jim, membership__type='admin')
+        self.assertEqual(list(jim_admins), [self.nerds])
+
+    def test_member_groups(self):
+        # And which groups is Bob just a member of?
+        bob_membership = Group.objects.filter(people=self.bob, membership__type='member')
+        self.assertEqual(list(bob_membership), [self.jocks, self.nerds])