/// <summary>
/// 为实体类强行添加一个rx_field，被添加rx_field只能通过rx_entity的键值对进行访问
/// <para>链式操作</para>
/// </summary>
/// <param name="key">key</param>
/// <param name="field">rx_field</param>
protected sealed override T add <T>(string key, rx_field field)
{
this.rx_entity.Add(key, field);
return(this as T);
}
/// <summary>
/// 为实体类强行添加一个rx_field，被添加rx_field只能通过rx_entity的键值对进行访问
/// <para>链式操作</para>
/// </summary>
/// <param name="key">key</param>
/// <param name="field">rx_field</param>
protected abstract T add <T>(string key, rx_field field)
where T : rx_strong_type, new();