说明：  有实例，讲解怎样更好的持久化，如何把数据库丢一边。优先设计业务层，将数据库层放在后边设计，并不是十分难的，恰恰相反，这种方式对于业务的理解，更加有好处。
(How better to explain persistence, how to throw aside the database. To give priority to the business layer, database layer on the back design, is not very difficult, on the contrary, this approach to understanding the business and more beneficial.)