/**
  * log given log message and set error string and error message string
  * @param string log_message human readable log message for this error
  * @param string error_message error message for user
  * @return void
  */
 function _handle_error($log_message, $error_message)
 {
     if (strlen($log_message) > 0) {
         $this->_log->error($log_message);
         $this->error_log_str = $log_message;
     } else {
         $this->error_log_str = "";
     }
     if (strlen($this->_database->get_error_str()) > 0) {
         $this->_log->error("database error: " . $this->_database->get_error_str());
         $this->error_str = $this->_database->get_error_str();
     } else {
         $this->error_str = "";
     }
     $this->error_message_str = $error_message;
 }