MDL-59367 participants: Reduce db queries

Fetch all role assignments for the course in a single query, instead of for each of the listed users.

More data but less queries.

lib/accesslib.php

@@ -2664,6 +2664,65 @@ function get_archetype_roles($archetype) {
     return $DB->get_records('role', array('archetype'=>$archetype), 'sortorder ASC');
 }
 
+/**
+ * Gets all the user roles assigned in this context, or higher contexts for a list of users.
+ *
+ * @param context $context
+ * @param array $userids. An empty list means fetch all role assignments for the context.
+ * @param bool $checkparentcontexts defaults to true
+ * @param string $order defaults to 'c.contextlevel DESC, r.sortorder ASC'
+ * @return array
+ */
+function get_users_roles(context $context, $userids = [], $checkparentcontexts = true, $order = 'c.contextlevel DESC, r.sortorder ASC') {
+    global $USER, $DB;
+
+    if ($checkparentcontexts) {
+        $contextids = $context->get_parent_context_ids();
+    } else {
+        $contextids = array();
+    }
+    $contextids[] = $context->id;
+
+    list($contextids, $params) = $DB->get_in_or_equal($contextids, SQL_PARAMS_NAMED, 'con');
+
+    // If userids was passed as an empty array, we fetch all role assignments for the course.
+    if (empty($userids)) {
+        $useridlist = ' IS NOT NULL ';
+        $uparams = [];
+    } else {
+        list($useridlist, $uparams) = $DB->get_in_or_equal($userids, SQL_PARAMS_NAMED, 'uids');
+    }
+
+    $sql = "SELECT ra.*, r.name, r.shortname, ra.userid
+              FROM {role_assignments} ra, {role} r, {context} c
+             WHERE ra.userid $useridlist
+                   AND ra.roleid = r.id
+                   AND ra.contextid = c.id
+                   AND ra.contextid $contextids
+          ORDER BY $order";
+
+    $all = $DB->get_records_sql($sql , array_merge($params, $uparams));
+
+    // Return results grouped by userid.
+    $result = [];
+    foreach ($all as $id => $record) {
+        if (!isset($result[$record->userid])) {
+            $result[$record->userid] = [];
+        }
+        $result[$record->userid][$record->id] = $record;
+    }
+
+    // Make sure all requested users are included in the result, even if they had no role assignments.
+    foreach ($userids as $id) {
+        if (!isset($result[$id])) {
+            $result[$id] = [];
+        }
+    }
+
+    return $result;
+}
+
+
 /**
  * Gets all the user roles assigned in this context, or higher contexts
  * this is mainly used when checking if a user can assign a role, or overriding a role

lib/tests/accesslib_test.php

@@ -1561,6 +1561,42 @@ class core_accesslib_testcase extends advanced_testcase {
         $this->assertSame('', $roles);
     }
 
+    /**
+     * Test get_user_roles and get_users_roles
+     */
+    public function test_get_user_roles() {
+        global $DB, $CFG;
+
+        $this->resetAfterTest();
+
+        $teacherrole = $DB->get_record('role', array('shortname'=>'editingteacher'), '*', MUST_EXIST);
+        $studentrole = $DB->get_record('role', array('shortname'=>'student'), '*', MUST_EXIST);
+        $course = $this->getDataGenerator()->create_course();
+        $coursecontext = context_course::instance($course->id);
+        $teacherrename = (object)array('roleid'=>$teacherrole->id, 'name'=>'Učitel', 'contextid'=>$coursecontext->id);
+        $DB->insert_record('role_names', $teacherrename);
+
+        $roleids = explode(',', $CFG->profileroles); // Should include teacher and student in new installs.
+
+        $user1 = $this->getDataGenerator()->create_user();
+        role_assign($teacherrole->id, $user1->id, $coursecontext->id);
+        role_assign($studentrole->id, $user1->id, $coursecontext->id);
+        $user2 = $this->getDataGenerator()->create_user();
+        role_assign($studentrole->id, $user2->id, $coursecontext->id);
+        $user3 = $this->getDataGenerator()->create_user();
+
+        $u1roles = get_user_roles($coursecontext, $user1->id);
+        
+        $u2roles = get_user_roles($coursecontext, $user2->id);
+
+        $allroles = get_users_roles($coursecontext);
+        $specificuserroles = get_users_roles($coursecontext, [$user1->id, $user2->id]);
+        $this->assertEquals($u1roles, $allroles[$user1->id]);
+        $this->assertEquals($u1roles, $specificuserroles[$user1->id]);
+        $this->assertEquals($u2roles, $allroles[$user2->id]);
+        $this->assertEquals($u2roles, $specificuserroles[$user2->id]);
+    }
+
     /**
      * Test has_capability(), has_any_capability() and has_all_capabilities().
      */

user/classes/participants_table.php

@@ -104,6 +104,11 @@ class participants_table extends \table_sql {
      */
     protected $allroles;
 
+    /**
+     * @var \stdClass[] List of roles indexed by roleid.
+     */
+    protected $allroleassignments;
+
     /**
      * @var \stdClass[] Assignable roles in this course.
      */
@@ -201,6 +206,7 @@ class participants_table extends \table_sql {
         $this->context = $context;
         $this->groups = groups_get_all_groups($courseid, 0, 0, 'g.*', true);
         $this->allroles = role_fix_names(get_all_roles($this->context), $this->context);
+        $this->allroleassignments = get_users_roles($this->context, [], true, 'c.contextlevel DESC, r.sortorder ASC');
         $this->assignableroles = get_assignable_roles($this->context, ROLENAME_ALIAS, false);
     }
 
@@ -258,7 +264,7 @@ class participants_table extends \table_sql {
     public function col_roles($data) {
         global $OUTPUT;
 
-        $roles = get_user_roles($this->context, $data->id, true, 'c.contextlevel DESC, r.sortorder ASC');
+        $roles = isset($this->allroleassignments[$data->id]) ? $this->allroleassignments[$data->id] : [];
         $getrole = function($role) {
             return $role->roleid;
         };