MDL-63686 core: Preload parent contexts

lib/accesslib.php

@@ -5434,6 +5434,9 @@ abstract class context extends stdClass implements IteratorAggregate {
             return array();
         }
 
+        // Preload the contexts to reduce DB calls.
+        context_helper::preload_contexts_by_id($contextids);
+
         $result = array();
         foreach ($contextids as $contextid) {
             $parent = context::instance_by_id($contextid, MUST_EXIST);
@@ -5870,6 +5873,35 @@ class context_helper extends context {
          context::preload_from_record($rec);
      }
 
+    /**
+     * Preload a set of contexts using their contextid.
+     *
+     * @param   array $contextids
+     */
+    public static function preload_contexts_by_id(array $contextids) {
+        global $DB;
+
+        // Determine which contexts are not already cached.
+        $tofetch = [];
+        foreach ($contextids as $contextid) {
+            if (!self::cache_get_by_id($contextid)) {
+                $tofetch[] = $contextid;
+            }
+        }
+
+        if (count($tofetch) > 1) {
+            // There are at least two to fetch.
+            // There is no point only fetching a single context as this would be no more efficient than calling the existing code.
+            list($insql, $inparams) = $DB->get_in_or_equal($tofetch, SQL_PARAMS_NAMED);
+            $ctxs = $DB->get_recordset_select('context', "id {$insql}", $inparams, '',
+                    \context_helper::get_preload_record_columns_sql('{context}'));
+            foreach ($ctxs as $ctx) {
+                self::preload_from_record($ctx);
+            }
+            $ctxs->close();
+        }
+    }
+
     /**
      * Preload all contexts instances from course.
      *