将iPhone应用程序与MySQL数据库连接的教程？ （使用mysql接口Objective-C）

I am looking for a tutorial on how to make an iPhone app that fetches data from and writes data to a MySQL database. I've seen some other threads saying that I should make an abstraction layer so as not to connect directly to the database from my app, but I'm not sure of how to actually go about doing this. Does anyone know of any tutorials that involve creating an abstraction layer for a MySQL database or connecting a MySQL database to an iPhone app?I am looking for a tutorial on how to make an i