使用 hibernate 的 DAO 和服务层
我在服务层的实现方面遇到了麻烦，我想我不太理解这个概念。
在 DAO 实现中，我可以为特定技术和实体（例如 hibernate 和 User 表）编写所有 CRUD 逻辑，并且在服务层中，我们使用 DAO 来对 DAO 中的实体进行所有数据操作（例如 getUser、loginUser 等） ..）这样可以吗？
如果可以的话，我有一个简单的问题，我可以在服务层、DAO 实现中处理数据库连接（或者在休眠、会话和事务的情况下）吗？
例如，我有一个简单的 GUI，带有一个按钮（加载所有用户），并且一张表将包含所有用户。按下按钮将加载所有用户的表。
我有一个用于用户实体（UserHibernateDAO）的 HibernateDAO，其中包含所有 CRUD 操作和一个服务层 UserService，用于与用户进行某些特定的数据操作。
ServiceLayer：
public class UserService extends AbstractServiceLayer{
private AbstractDAO dao;
public UserService(AbstractDAO dao){
this.dao=dao;
}
public List<User> loadAllUsers(){
return dao.findAll();
}
}
Button的actionperformed中：
private void buttonActionPerformed(ActionEvent evt) {
Transaction transaction=HibernateUtil.getSessionFactory().getCurrentSession().beginTransaction();
List<User> users=userService.loadAllUsers();
loadTableWithUsers(users);
transaction.commit();
}
这样实现可以吗？ 会话和事务句柄位于正确的位置还是我必须将其放入服务层？ ..或者也许进入 dao ？
EDIT1：
如果我有一个 UserDAO 接口和一个实现 UserDAO 的 UserHibernateDAO，服务层就没有理由存在，不是吗？ 因为我可以拥有所有方法来管理我的 UserDAO 中的“USER”，并且 UserHibernateDAO 实现了休眠技术的所有这些方法...然后我可以拥有 UserJdbcDAO、UserMysqlDAO 等...嗯...
EDIT2:
private void buttonActionPerformed(ActionEvent evt) {
myBusinessMethod();
}
private void myBusinessMethod(){
Transaction transaction=HibernateUtil.getSessionFactory().getCurrentSession().beginTransaction();
List<User> users=userService.loadAllUsers();
loadTableWithUsers(users);
//some other useful operation before close session
transaction.commit();
}
我不确定，业务方法是这样的方法吗？
谢谢大家。
im in trouble with implemenetation of a service layer, i think i did not understand this concept very well.
In a DAO implementation i can write all CRUD logic for a specific technology and entity (for example hibernate and User table), and in a service layer we use a DAO for all data operation for the entity in DAO (like getUser, loginUser, etc..) is this ok?
If this is ok i have a simple question, can i handle database connection (or in case of hibernate, session and transaction) within service layer, DAO implementation or neither?
Example, i have a simple GUI with one Button(load all User), and a table will contains all User. Pressing the Button will load the table with all users.
I have a HibernateDAO for User entity (UserHibernateDAO) containing all CRUD operation and a service layer, UserService, for some specific data operation with user.
ServiceLayer:
public class UserService extends AbstractServiceLayer{
private AbstractDAO dao;
public UserService(AbstractDAO dao){
this.dao=dao;
}
public List<User> loadAllUsers(){
return dao.findAll();
}
}
In actionperformed of Button:
private void buttonActionPerformed(ActionEvent evt) {
Transaction transaction=HibernateUtil.getSessionFactory().getCurrentSession().beginTransaction();
List<User> users=userService.loadAllUsers();
loadTableWithUsers(users);
transaction.commit();
}
Is this implementation ok?
Session and transaction handle is in the right position or i have to put it into service layer? ..or perhaps into dao?
EDIT1:
If i have an interface UserDAO and a UserHibernateDAO that implements UserDAO, service layer has no reason to exists, isn't true?
Becouse i can have all method to manage an "USER" inside my UserDAO and UserHibernateDAO implements all this methods for hibernate technology... then i could have a UserJdbcDAO, UserMysqlDAO etc... mmm...
EDIT2:
private void buttonActionPerformed(ActionEvent evt) {
myBusinessMethod();
}
private void myBusinessMethod(){
Transaction transaction=HibernateUtil.getSessionFactory().getCurrentSession().beginTransaction();
List<User> users=userService.loadAllUsers();
loadTableWithUsers(users);
//some other useful operation before close session
transaction.commit();
}
im not sure, a business method is a method like this?
Thanks all.
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评论（1）
actionPerformed()方法内处理事务。它显然违背了 DAO/Service 层的目的现在，没什么建议。
Service、DAO和BusinessDelegate。所以，问问自己这些是否真的能回答你的一些问题。如果没有，就摆脱它们。 YAGNI[已编辑]
在您编辑之后，我的第三个建议没有多大意义。顺便说一句，您将 DAO 命名如下；
UserJdbcDAO、UserMysqlDAO等。您的第二个名称没有多大意义，因为我们使用 ORM 只是为了避免数据库供应商特定的 DAO/查询。如果您的UserMysqlDAO 扩展了 UserJdbcDAO，它可能会开始有意义。actionPerformed()method. Its clearly defeating the purpose of DAO/Service layerUserServiceis acceptingAbstractDAO, which means some other code may pass wrong DAO implementation to yourUserServicethat will screw things upNow, few suggestions.
Service,DAOandBusinessDelegate. So, question yourself are any of these really answering some of your questions. If not, get rid of them. YAGNI[Edited]
After your edit my 3rd suggestion doesn't carry much weight. By the way, you name your DAOs as follows;
UserJdbcDAO,UserMysqlDAOetc. Your 2nd name is not making much sense, as we use ORMs just to avoid DB vendor specific DAOs/queries. It might start making some sense if yourUserMysqlDAO extends UserJdbcDAO.