Activities get deleted when case deleted.

modules/opencase_cases/opencase_cases.module

@@ -79,6 +79,20 @@ function opencase_cases_get_case_fees(Drupal\opencase_cases\entity\OCCase $case)
   return $case_fees;
 }
 
+/**
+ * @return Drupal\opencase_cases\entity\OCActivity[]
+ */
+function opencase_cases_get_activities(Drupal\opencase_cases\entity\OCCase $case): array {
+  $query = \Drupal::entityQuery('oc_activity')
+    ->condition('oc_case.target_id', $case->id());
+  $activity_ids =  $query->execute();
+  $activities = [];
+  foreach($activity_ids as $id) {
+    $activities[] = Drupal\opencase_entities\Entity\OCActivity::load($id);
+  }
+  return $activities;
+}
+
 function opencase_cases_get_amount(Drupal\opencase_cases\entity\OCCaseFee $case_fee): string {
   return $case_fee->amount->first()->value;
 }
@@ -132,6 +146,15 @@ function opencase_cases_entity_base_field_info($entity_type) {
   return $fields;
 }
 
+// When deleting a case, delete the activities associated with it
+function opencase_cases_oc_case_delete(Drupal\opencase_cases\Entity\OCCase $case): void {
+  $activities = opencase_cases_get_activities($case);
+  foreach ($activities as $activity) {
+    $activity->delete();
+  }
+}
+
+
 /**
  * When creating an activity, it sets the case id from the URL.
  */