protected function _set_where($params)
    {
        if (count($params) == 1)
        {
            $this->_database->where($params[0]);
        }
        else if(count($params) == 2)
        {
            $this->_database->where($params[0], $params[1]);
        }
        else if(count($params) == 3)
        {
            $this->_database->where($params[0], $params[1], $params[2]);
        }
        else
        {
            $this->_database->where($params);
        }
    }