Persisting transient objects.

matiello · **Posted:** Thu Feb 05, 2004 3:32 pm

Hello.

I'm having a basic problem. Maybe this problem relies on how my application uses hibernate 2.1 with Tomcat 5.0.16.

I'm developing a simple WEB application that interacts with database throw hibernate framework.

So, supose the following scenario:

User at page ShowUserInformation.jsp clicks on button delete, which sends the user to another JSP (say, UserDelete.jsp) page that receives use userId as parameter.

At page UserDelete.jsp, I will use hibernate to delete the UserData (the table key is user_id) object from database, with something like this:

Code:

UserData user = new UserData();
user.setUserId(request.getParameter("userId"));
tx = session.beginTransaction();
session.delete(user);
tx.commit();

However,at this point, it throws an exception that user object is not persistent since some of its atributes are "not-null".

I wonder, the only way to delete this object from database is to use a custom delete HSQL statement? Of course, I can get the persistent object from database and them delete it.

I understand that my approach might be wrong. How would be a good aproach for solving this "problema" since I don't wanna "go" again to the dabase to get the persistent user and them delete him.

I hope I made my self clear.

Regards,

Flavio Matiello

emmanuel · **Posted:** Thu Feb 05, 2004 3:54 pm

No, but why delete(HQL) is so hard ?

matiello · **Posted:** Fri Feb 06, 2004 8:56 am

No, its not that hard.

However, Hibernate could provide a method like delete(keyParam),
just like we use on load operation.

Maybe there's a way to do this that I'm not aware of.

Imagine if my table has a primary key based on 4 colums.
I must provite a HQL statement with four parameters and four types, which could be replaced by a singe EntityPK object. Know what I mean?

Regards,

Flavio Matiello

emmanuel · **Posted:** Fri Feb 06, 2004 9:32 am

This has been discussed either on the forum or in JIRA. Have a look. I can remember Gavin wasn't fond of.

matiello · **Posted:** Fri Feb 06, 2004 5:18 pm

Yes, I found it on JIRA emmanuel.

Just another thing, according to the hibernate sql logs generated, when I execute a delete with HQL query, it in fact, executes a select and a delete right? I mean, It interact 2 times with the database....

Following the above reasoning, what if I execute a delete with a HQL query to delete a lot of records, it would interact several times with the database, or just two times.

Thanks in advance,

Fl

christian · **Posted:** Fri Feb 06, 2004 5:21 pm

All objects have to be loaded (at least lazily) so cascading and lifecycle operations can be applied before deletion. Mass deletes (and updates) are not a good usecase for Hibernate (and ORM in general). Those usecases are usually rare in an application, if you need best performance, use a direct JDBC SQL call or a stored procedure.