Add support for replicating course enrollment/unenrollment to course databases

common/djangoapps/student/models.py

@@ -10,14 +10,21 @@ file and check it in at the same time as your model changes. To do that,
 """
 from datetime import datetime
 import json
+import logging
 import uuid
 
-from django.db import models
+from django.conf import settings
 from django.contrib.auth.models import User
+from django.db import models
+from django.db.models.signals import post_delete, post_save
+from django.dispatch import receiver
 from django_countries import CountryField
 
+from xmodule.modulestore.django import modulestore
+
 #from cache_toolbox import cache_model, cache_relation
 
+log = logging.getLogger(__name__)
 
 class UserProfile(models.Model):
     class Meta:
@@ -203,3 +210,59 @@ def add_user_to_default_group(user, group):
         utg.save()
     utg.users.add(User.objects.get(username=user))
     utg.save()
+
+
+
+
+
+################################# SIGNALS ######################################
+
+def is_valid_course_id(course_id):
+    """We check to both make sure that it's a valid course_id (and not 
+    'default', or some other non-course DB name) and that we have a mapping
+    for what database it belongs to."""
+    course_ids = set(course.id for course in modulestore().get_courses())
+    return (course_id in course_ids) and (course_id in settings.DATABASES)
+
+def is_portal():
+    """Are we in the portal pool? (in which case we'll have to replicate user
+    updates). Right now, that means we have more than one database defined."""
+    return len(settings.DATABASES) > 1
+
+def replicate_enrollment(instance_method, **kwargs):
+    log.debug("########## Enrollment replication called ############")
+    instance = kwargs['instance']
+
+    if not is_portal():
+        log.debug("replicate_enrollment triggered, but we're not a portal so " +
+                  "we're not propogating")
+        return
+
+    if not is_valid_course_id(instance.course_id):
+        log.error("Don't know where to replicate to for course_id: {0}"
+                  .format(instance.course_id))
+        return
+
+    # We create a _replicated attribute to differentiate the first save of this
+    # model vs. the duplicate save we force on to the course database.
+    if hasattr(instance, '_replicated'):
+        log.debug("We've already replicated this -- stopping so we don't go " +
+                  "into an infinite loop.")
+        return 
+    instance._replicated = True
+
+    # instance_method is either CourseEnrollment.save or CourseEnrollment.delete
+    # using is the entry in DATABASES we push to (we use course_ids for names)
+    instance_method(instance, using=instance.course_id)
+
+@receiver(post_save, sender=CourseEnrollment)
+def replicate_enrollment_save(sender, **kwargs):
+    return replicate_enrollment(CourseEnrollment.save, **kwargs)
+
+@receiver(post_delete, sender=CourseEnrollment)
+def replicate_enrollment_delete(sender, **kwargs):
+    return replicate_enrollment(CourseEnrollment.delete, **kwargs)
+
+
+
+