读hibernate in action 和 PEAA 后发现感到的迷惑

Handling Finders
In order to work with an object, you have to load it from the database. Usually the presentation layer will initiate things by loading some initial objects. Then control moves into the domain layer, at which point the code will mainly move from object to object using associations between them. This will work effectively providing that the domain layer has all the objects it needs loaded into memory or that you use Lazy Load (200) to load in additional objects when needed.

On occasion you may need the domain objects to invoke find methods on the Data Mapper. However, I've found that with a good Lazy Load (200) you can completely avoid this. For simpler applications, though, may not be worth trying to manage everything with associations and Lazy Load (200). Still, you don't want to add a dependency from your domain objects to your Data Mapper.

You can solve this dilemma by using Separated Interface (476). Put any find methods needed by the domain code into an interface class that you can place in the domain package.

首先来说，文件系统和数据库两回事，没有什么类比关系，这个例子也举得不好，何况你的DAO设计的也不合理。



1)

File file = new File();;
file.setFolder(folder);;
file.setName(name);;
file.set.....;

fileDao.addFile(file);;

2)

file.setName(newFileName);;

fileDao.updateFile(file);;

3)

file.setFolder(newFolder);;

fileDao.updateFile(file);;

这种情况下lazy不lazy对你来说完全透明!

List orderItems = orderDao.getOrderItems(order);

You can solve this dilemma by using Separated Interface (476). Put any find methods needed by the domain code into an interface class that you can place in the domain package.

我感觉robbin没完全理解我的意思。

从这些代码中看不出业务限制是在那里实现的，难道是要在fileDao中各个方法里面进行name是否重复的判定么？在DAO里面实现业务限制？

另外解释一下，这里只是举个例子，其实可以把这个例子想象成一个基于数据库的文件系统的设计。

希望robbin能继续这个讨论。

问题时你这样做:

根本不透明阿,倒是我的方法比较透明一点,order.getItems();是不是lazy的order的用户根本不需要知道.order.getProductsInfo();也一样更加自然 order 拥有它的数据和它的行为。


interface class that you can place in the domain package！

什么叫做业务限制？什么叫做name是否重复的判定？不知道你在说什么。

我给出来的代码就是你上面给出来的代码的修正。

DomainObject： folder 1 ---- * file
（这里仅仅是用Folder和File做个比喻，因为是计算机上最常见的东西，容易理解）

业务限制： file.name 在 folder 中唯一（同一目录中不能包含相同名字的文件）。