public function addFieldAlias($field, $alias) {
        $added = false;
        if (array_key_exists($field, $this->_fields)) {
            if (!array_key_exists($alias, $this->_fields)) {
                $this->_fields[$alias] =& $this->_fields[$field];
                if (!array_key_exists($alias, $this->_fieldAliases)) {
                    $this->_fieldAliases[$alias] = $field;
                    if (!array_key_exists($alias, $this->xpdo->map[$this->_class]['fieldAliases'])) {
                        $this->xpdo->map[$this->_class]['fieldAliases'][$alias]= $field;
                    }
                }
                $added = true;
            } else {
                $this->xpdo->log(xPDO::LOG_LEVEL_ERROR, "The alias {$alias} is already in use as a field name in objects of class {$this->_class}", '', __METHOD__, __FILE__, __LINE__);
            }
        }
        return $added;
    }