public function getField($name)
    {
        if (array_key_exists($name, $this->fields)) {
            return $this->fields[$name];
        }
        else if (array_key_exists($name, $this->fieldAliases)) {
            $name = $this->fieldAliases[$name];
            return $this->fields[$name];
        }
        return null;
    }