get_cohort() function and test

common/djangoapps/course_groups/models.py

@@ -23,5 +23,32 @@ class CourseUserGroup(models.Model):
 
     # For now, only have group type 'cohort', but adding a type field to support
     # things like 'question_discussion', 'friends', 'off-line-class', etc
-    GROUP_TYPE_CHOICES = (('cohort', 'Cohort'),)
+    COHORT = 'cohort'
+    GROUP_TYPE_CHOICES = ((COHORT, 'Cohort'),)
     group_type = models.CharField(max_length=20, choices=GROUP_TYPE_CHOICES)
+
+
+def get_cohort(user, course_id):
+    """
+    Given a django User and a course_id, return the user's cohort.  In classes with
+    auto-cohorting, put the user in a cohort if they aren't in one already.
+
+    Arguments:
+        user: a Django User object.
+        course_id: string in the format 'org/course/run'
+
+    Returns:
+        A CourseUserGroup object if the User has a cohort, or None.
+    """
+    group_type = CourseUserGroup.COHORT
+    try:
+        group = CourseUserGroup.objects.get(course_id=course_id, group_type=group_type,
+                                        users__id=user.id)
+    except CourseUserGroup.DoesNotExist:
+        group = None
+    
+    if group:
+        return group
+
+    # TODO: add auto-cohorting logic here
+    return None

common/djangoapps/course_groups/tests/tests.py

+from django.contrib.auth.models import User
+from nose.tools import assert_equals
+
+from course_groups.models import CourseUserGroup, get_cohort
+
+def test_get_cohort():
+    course_id = "a/b/c"
+    cohort = CourseUserGroup.objects.create(name="TestCohort", course_id=course_id,
+                           group_type=CourseUserGroup.COHORT)
+
+    user = User.objects.create(username="test", email="a@b.com")
+    other_user = User.objects.create(username="test2", email="a2@b.com")
+
+    cohort.users.add(user)
+
+    got = get_cohort(user, course_id)
+    assert_equals(got.id, cohort.id, "Should find the right cohort")
+
+    got = get_cohort(other_user, course_id)
+    assert_equals(got, None, "other_user shouldn't have a cohort")
+