/**
  * appends sql to given select statement
  *
  * @param Zend_Db_Select                $_select
  * @param Tinebase_Backend_Sql_Abstract $_backend
  */
 public function appendFilterSql($_select, $_backend)
 {
     $db = $_backend->getAdapter();
     // prepare value
     $value = $this->_value ? 1 : 0;
     if ($value) {
         // nothing to do -> show all contacts!
         if (Tinebase_Core::isLogLevel(Zend_Log::DEBUG)) {
             Tinebase_Core::getLogger()->debug(__METHOD__ . '::' . __LINE__ . ' Query all account contacts.');
         }
     } else {
         if (Tinebase_Core::isLogLevel(Zend_Log::DEBUG)) {
             Tinebase_Core::getLogger()->debug(__METHOD__ . '::' . __LINE__ . ' Only query visible and enabled account contacts.');
         }
         if (Tinebase_Core::getUser() instanceof Tinebase_Model_FullUser) {
             $where = '/* is no user */ ' . Tinebase_Backend_Sql_Command::getIfIsNull($db, $db->quoteIdentifier('accounts.id'), 'true', 'false') . ' OR /* is user */ (' . Tinebase_Backend_Sql_Command::getIfIsNull($db, $db->quoteIdentifier('accounts.id'), 'false', 'true') . ' AND ' . $db->quoteInto($db->quoteIdentifier('accounts.status') . ' = ?', 'enabled') . " AND " . '(' . $db->quoteInto($db->quoteIdentifier('accounts.visibility') . ' = ?', 'displayed') . ' OR ' . $db->quoteInto($db->quoteIdentifier('accounts.id') . ' = ?', Tinebase_Core::getUser()->getId()) . ')' . ")";
         } else {
             $where = '/* is no user */ ' . Tinebase_Backend_Sql_Command::getIfIsNull($db, $db->quoteIdentifier('accounts.id'), 'true', 'false') . ' OR /* is user */ (' . Tinebase_Backend_Sql_Command::getIfIsNull($db, $db->quoteIdentifier('accounts.id'), 'false', 'true') . ' AND ' . $db->quoteInto($db->quoteIdentifier('accounts.status') . ' = ?', 'enabled') . " AND " . $db->quoteInto($db->quoteIdentifier('accounts.visibility') . ' = ?', 'displayed') . ")";
         }
         $_select->where($where);
         $select = $_select instanceof Zend_Db_Select ? $_select : $_select->getSelect();
         $select = Tinebase_Backend_Sql_Abstract::traitGroup($db, $_backend->getTablePrefix(), $select);
         $_select instanceof Zend_Db_Select ? $_select = $select : $_select->setSelect($select);
         if (Tinebase_Core::isLogLevel(Zend_Log::DEBUG)) {
             Tinebase_Core::getLogger()->debug(__METHOD__ . '::' . __LINE__ . ' contacts query ' . $_select->assemble());
         }
     }
 }