MDL-45500 gradingform: allow plugin uninstall

lib/classes/plugininfo/gradingform.php

@@ -31,6 +31,30 @@
 class gradingform extends base {
 
     public function is_uninstall_allowed() {
-        return false;
+        return true;
+    }
+
+    /**
+     * Pre-uninstall hook.
+     * This is intended for disabling of plugin, some DB table purging, etc.
+     */
+    public function uninstall_cleanup() {
+        global $DB;
+
+        // Find all definitions and templates.
+        $definitions = $DB->get_fieldset_select('grading_definitions', 'id', 'method = ?', [$this->name]);
+        if ($definitions) {
+            // Delete instances and definitions. Deleting instance will not delete grades because they were
+            // already pushed to the module and gradebook.
+            list($sqld, $paramsd) = $DB->get_in_or_equal($definitions);
+            $DB->delete_records_select('grading_instances', 'definitionid ' . $sqld, $paramsd);
+            $DB->delete_records_select('grading_definitions', 'id ' . $sqld, $paramsd);
+        }
+        // Delete templates for this grading method.
+        $DB->delete_records_select('grading_areas', 'component = ? AND activemethod = ?', array('core_grading', $this->name));
+        // Update the remaining grading areas to use simple grading method instead of this grading method.
+        $DB->execute('UPDATE {grading_areas} SET activemethod = NULL WHERE activemethod = ?', [$this->name]);
+
+        parent::uninstall_cleanup();
     }
 }