MDL-42299 course: management category expansion improvements

lib/db/caches.php

@@ -196,4 +196,13 @@ $definitions = array(
         'mode' => cache_store::MODE_APPLICATION,
         'simplekeys' => true,
     ),
+    // This is the session user selections cache.
+    // It's a special cache that is used to record user selections that should persist for the lifetime of the session.
+    // Things such as which categories the user has expanded can be stored here.
+    // It uses simple keys and simple data, please ensure all uses conform to those two constraints.
+    'userselections' => array(
+        'mode' => cache_store::MODE_SESSION,
+        'simplekeys' => true,
+        'simpledata' => true
+    ),
 );