/**
  * Adds a topic to a user's list of email subscriptions.
  *
  * @param  tx_mmforum_pi1  $forumObj The plugin object
  * @return string           An error message in case the redirect attempt to
  *                          the previous page fails.
  */
 static function set($forumObj)
 {
     $feUserId = intval($GLOBALS['TSFE']->fe_user->user['uid']);
     $forumId = intval($forumObj->piVars['fid']);
     // Executing database operations
     $res = $GLOBALS['TYPO3_DB']->exec_SELECTquery('uid', 'tx_mmforum_forummail', 'user_id = ' . $feUserId . ' AND forum_id = ' . $forumId . $forumObj->getStoragePIDQuery());
     if ($GLOBALS['TYPO3_DB']->sql_num_rows($res) < 1) {
         $insertArray = array('pid' => $forumObj->getStoragePID(), 'tstamp' => $GLOBALS['EXEC_TIME'], 'crdate' => $GLOBALS['EXEC_TIME'], 'forum_id' => $forumId, 'user_id' => $feUserId);
         $GLOBALS['TYPO3_DB']->exec_INSERTquery('tx_mmforum_forummail', $insertArray);
     }
     // Redirecting visitor back to previous page
     $forumObj->redirectToReferrer();
     return $forumObj->pi_getLL('subscr.addSuccess') . '<br />' . $forumObj->pi_getLL('redirect.error') . '<br />';
 }