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Re:Spring&Hibernate框架的程序设计 [Re:linux_china]

floater

Java Jedi

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发贴: 3233
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于 2005-05-09 03:00

My two cents:

User 在这里仅是一个PO对象，而不是实际生活中的BO(Business Object)对象

Actually, the most current opinion is that User is not PO. User is either an business object from the business layer, or an interface to be exposed to the lower persisitance layer. Note that this User, if it's an interface, may not be the entire business object interface, may be just the relevent portion to persistance. Basically, we use interfaces to shield/expose only the relevent methods,etc.

这里有人提出UserDao接口，这是一个什么角色？UserDao在我的眼中，它就
是一个工具类，将相关的操作整合到一个Java 接口中，没有依据一定的OO 设计方法。

Actually, UserDao is subject to the User context, so we still follow OO in that context, e.g., you dont' want to do irrelevent ops to User. So this is really not a tool class, more of a business object itself. For example, if your business doesn't have update method, then your DAO shouldn't have that.

If I understand you correctly, you try to seperate the DAO class to two: User for User specific operations, and UserHome for "general, non db" operations. You are annoyed by the fact that too much info are binded to the DAO class. I think this is the most commonly-seen misconception in the chinese community, here, javaeye, and others. The key is that DAO is belonging to the business layer(Rod mentioned in his second book with one line, and I specifically drew a char in my ibatis and spring doc). This one single fact has a very huge implicaiton to quite a few things. Most of the arguments in the chinese java community are based on just the opposite of this concept. The DAO interface should not have anything specific to database or any specific implementation(I could use a simple file for storage too). The DAO should obey rules in the middle layer as well. In the pre Spring era, due the transaction processes, there should be another very thin sublayer(of the middle layer) setting between persistance layer and business layer. This is very annoying and creates confusion too(I personally think that this thin layer is one of the root causes for the confusion in our community(Another cause is just that DAO shouldn't have any implementation details, but more and more folks become aware of this now).

Therefore, since DAO should have only dependencies in the middle layer, your User class can be combined with the UserHome class, which has the same characteristics. In fact, whether to split it into several classes is up to the business logic. For example, we discussed a case in here when we have some kind of search spinning across several tables, or more general, search across several different directions(This means, no matter what implementation you use, it's likely to seperate these different concerns anyway).

floater edited on 2005-05-23 09:22

"Any fool can write code that a computer can understand. Good programmers write code that humans can understand."
- Martin Fowler, Refactoring - Improving the Design of Existing Code

话题树型展开

人气	标题	作者	字数	发贴时间
17202	Spring&Hibernate框架的程序设计	linux_china	115	2005-05-07 16:55
13855	Re:Spring&Hibernate框架的程序设计	steven_652	35	2005-05-07 20:31
14554	Re:Spring&Hibernate框架的程序设计	floater	2732	2005-05-09 03:00
13556	Re:Spring&Hibernate框架的程序设计	jigsaw	1225	2005-05-22 17:05
13527	Re:Spring&Hibernate框架的程序设计	jigsaw	489	2005-05-22 17:37
13415	Re:Spring&Hibernate框架的程序设计	floater	2074	2005-05-23 09:18
13595	Re:Spring&Hibernate框架的程序设计	linux_china	286	2005-05-23 19:17
13369	Re:Spring&Hibernate框架的程序设计	jigsaw	318	2005-05-23 16:22
13563	Re:Spring&Hibernate框架的程序设计	floater	431	2005-05-23 21:47
16076	Re:Spring&Hibernate框架的程序设计	ben_nb	28	2005-06-15 12:21

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