fix: send LEARNER_CREDIT_COURSE_ENROLLMENT_REVOKED from the correct p…

…lace.

I had originally tried emitting this event from the `/cancel_enrollment`
API endpoint, but in reality the LMS and Enterprise dashboards were
calling the `/change_enrollment` endpoint.  The former is called by
enterprise-subsidy on transaction reversal, i.e. NOT learner-initiated.
The latter is learner-initiated, and that's the original goal of this
work.

ENT-9213

enterprise/models.py

@@ -60,7 +60,6 @@
     json_serialized_course_modes,
 )
 from enterprise.errors import LinkUserToEnterpriseError
-from enterprise.event_bus import send_learner_credit_course_enrollment_revoked_event
 from enterprise.logging import getEnterpriseLogger
 from enterprise.tasks import send_enterprise_email_notification
 from enterprise.utils import (
@@ -2288,8 +2287,6 @@ def revoke(self):
         Marks this object as revoked and marks the associated EnterpriseCourseEnrollment
         as "saved for later".  This object and the associated EnterpriseCourseEnrollment are both saved.
 
-        Subclasses may override this function to additionally emit revocation events.
-
         TODO: revoke entitlements as well?
         """
         if self.enterprise_course_enrollment:
@@ -2333,13 +2330,6 @@ class LearnerCreditEnterpriseCourseEnrollment(EnterpriseFulfillmentSource):
     .. no_pii:
     """
 
-    def revoke(self):
-        """
-        Revoke this LearnerCreditEnterpriseCourseEnrollment, and emit a revoked event.
-        """
-        super().revoke()
-        send_learner_credit_course_enrollment_revoked_event(self)
-
     def reactivate(self, transaction_id=None, **kwargs):
         """
         Idmpotently reactivates this LearnerCreditEnterpriseCourseEnrollment.

enterprise/signals.py

@@ -13,6 +13,7 @@
 from enterprise.api import activate_admin_permissions
 from enterprise.api_client.enterprise_catalog import EnterpriseCatalogApiClient
 from enterprise.decorators import disable_for_loaddata
+from enterprise.event_bus import send_learner_credit_course_enrollment_revoked_event
 from enterprise.tasks import create_enterprise_enrollment
 from enterprise.utils import (
     NotConnectedToOpenEdX,
@@ -394,6 +395,19 @@ def enterprise_unenrollment_receiver(sender, **kwargs):     # pylint: disable=un
         enterprise_enrollment.unenrolled_at = localized_utcnow()
         enterprise_enrollment.save()
 
+        # Emit LC revoked event if there's a related LC fulfillment.
+        try:
+            lc_fulfillment = enterprise_enrollment.learnercreditenterprisecourseenrollment_enrollment_fulfillment
+        except enterprise_enrollment.RelatedObjectDoesNotExist:
+            lc_fulfillment = None
+        if lc_fulfillment:
+            send_learner_credit_course_enrollment_revoked_event(lc_fulfillment)
+        else:
+            logger.info(
+                "No related LearnerCreditCourseEnrollment found for recently unenrolled EnterpriseCourseEnrollment for "
+                f"user {enrollment.user} and course {enrollment.course.course_key}. Skipping sending revoked event."
+            )
+
 
 def create_enterprise_enrollment_receiver(sender, instance, **kwargs):     # pylint: disable=unused-argument
     """