持久的Java实体参考问题

Question

I am working on a personal project, and i have a strange issue which i can't seem to solve, even after many hours of research and debugging, so obviously it must be somehting very simple i'm ignoring .... Anyway, the context is : JPA + PostgresSQL + Glassfish. I have an entity (generated by netbeans), MvUser, with:

@Id
@Basic(optional = false)
@NotNull
@Column(name = "id")
@SequenceGenerator(name="mv_user_autoincrement_gen",sequenceName     ="mv_user_autoincrement",allocationSize=1)  
@GeneratedValue(strategy=GenerationType.IDENTITY, generator="mv_user_autoincrement_gen") 
private Long id;

Then, i have an AbstractFacade with generics for all the boilerplate persistence code.
Here i have a method which doesn't do much, just:

@Override
public void create(T entity) {
    getEntityManager().persist(entity);
}

Now, let's say i call this in my service class: First i inject my facade:

@EJB
IMvUserFacade userFacade;

then i'll use it:

@Override
public void saveUser(MvUser user)
{
    userFacade.create(user);
    // more business specific code follows
}  

I make a call to the service like this

MvUser = new MvUser();
... setters etc
mvUserService.saveUser(user);

Now, what is happening is that in the create method the object is persisted, i have the generated id and everything. Because on the whole chain i have object parameters, i'm presuming that at the saveUser level the same object will be found, but no, i am left with a detached entity. What i'm doing wrong? Thanks.

Answer 1

If I understand you correctly, you want to search for the object you saved in create(). I think the object is not yet persisted to database, what you retrieve is the object from first-level cache, http://www.tutorialspoint.com/hibernate/hibernate_caching.htm , since you are still within transaction. If you try to retrieve the object as follow and the method saveUser() is not within transaction you will get the user object from database (but detached since outside transaction):

public void saveUser(MvUser user)
{
userFacade.create(user);
userFacade.get(userId);
// more business specific code follows
}