Check if object exists in database WITHOUT using Session.get

Nitzer_Ebb · **Posted:** Wed Feb 11, 2004 11:09 am

I wonder if it's possible to check if an object exists in the database without using the Session.get(Class clazz, Serializable id) method ?

I want to be able to do this check at anytime in the application. When using the Session.get(Class clazz, Serializable id) method, it's required that the object to check for is associated with the Session. I want to avoid this.

Is this possbly to achieve ?

Regards

Ps. I want this to be quite generic, i.e I don't want to write a lot of SQL/HQL to query the database. Ds.

Nitzer_Ebb · **Posted:** Wed Feb 11, 2004 11:36 am

Some more explanation. I have the following code where I try to
retrieve an object of class CommsIn ( this is obj in the parameter list )from the database :

public void check( Object obj ) throws PersistenceException
{
Session sess;

try
{

sess = sessionFactory.openSession();

Object o = sess.get(obj.getClass(),sess.getIdentifier(obj));

sess.close();

}
catch ( Throwable e )
{}
finally
{}
}

I got this Exception :

[11/02/04 16:33:41][WFlowP0 ][ERROR] com.hp.mw.csf.AccessManager - cannot create object of type test.CommsIn The instance was not associated with this session

Therefore I wonder, how to check if an object is already in the database at ANY time during runtime without using Session.get-method

jfifield · **Joined:** Tue Aug 26, 2003 3:09 pm **Posts:** 58

Well, first of all, you are calling session.getIdentifier(), which the api docs states:

Quote:

Return the identifier of an entity instance cached by the Session, or throw an exception if the instance is transient or associated with a different Session.

So if you just pass the actual identifier value to session.get(), it will work. Of course, this will result in associating the loaded object with the session. If that's not what you want, then you could do a simple select count(*) from classname where id = ?

Nitzer_Ebb · **Posted:** Wed Feb 11, 2004 12:13 pm

But the identifier has to be Serializable, and in this case it is just a String.

It seems avoiding SQL may be hard in this case :=(

jfifield · **Joined:** Tue Aug 26, 2003 3:09 pm **Posts:** 58

A String is Serializable. I don't understand what the problem is.[/i]

emmanuel · **Posted:** Wed Feb 11, 2004 12:26 pm

you can get an object that isn't yet associated to the session.
But you can't session.getIndetifier(obj); on a non associated object.

try

Code:

obj = session.get(myclass, myId);
session.evict(obj);

If you want to evict the object after retrieving it.

Every identifiers must be Serializable in Hibernate.

Code:

Object o = sess.get(obj.getClass(),sess.getIdentifier(obj));

is pretty useless, it'll basically do

Code:

Object o = obj;