Which method of Session should I choose?

timeguest · **Joined:** Thu Nov 10, 2005 11:05 pm **Posts:** 4

Hi,
I have an object deserialized from XML ( through XStream ), which method of Session should I use to save the object to DB? Before I save it, neither do I know if there is an instance of this object associated with the session, nor if there is a record with the same id in db. What can I do to handle this situation?
Thanks a lot!

kgignatyev · **Posted:** Wed Nov 16, 2005 11:23 pm

If mapping specifies unsaved value for object id (null) then session.saveOrUpate( object ) will insert or update record depending on value of ID of the deserialized object.
Otherwise you need to search DB for an object and if it is present then session.merge( object ) , or session.save(object) if not.
Depending on mapping you may need to assign identifier ( when generator=”assigned”).

timeguest · **Joined:** Thu Nov 10, 2005 11:05 pm **Posts:** 4

The object has a composite id, so specify unsaved-value to null is invalid. And how can I query the presence of the record with the same id as this object? Hibernate3's load method requires an Identifier which must be obtained from a persitent object.

SleepyBear · **Joined:** Sat Oct 22, 2005 11:16 pm **Posts:** 40

Composite IDs are bad in general. In this case they are even more bad.

Every row in a table should have a unique ID number. Why fight it?

timeguest · **Joined:** Thu Nov 10, 2005 11:05 pm **Posts:** 4

Legacy db always exists. There's no reason or need to force legacy system to think in hibernate's way.

kgignatyev · **Posted:** Thu Nov 17, 2005 12:03 pm

to find out if there is such object do:
q = session.createQuery( "from YourClass yc where yc.id.part1= :p1 and yc.id.part2=:p2");
q.set( "p1" ....
if( q.list().size() == 0 ){
insert new (save(x) )
}else{
update ( session.merge(x))
}

snpesnpe · **Joined:** Sat Jun 12, 2004 4:49 pm **Posts:** 915

or simple call

Code:

try {
  session.load(YourObject.class, yourObject);
  exists=true;
} catch (HibernateException e) {
  exists=false;
}

kgignatyev · **Posted:** Thu Nov 17, 2005 3:38 pm

IMO application logic must not rely on Exception for normal course of operations.

SleepyBear · **Joined:** Sat Oct 22, 2005 11:16 pm **Posts:** 40

kgignatyev wrote:

IMO application logic must not rely on Exception for normal course of operations.

I agree. Exceptions are for exceptional events.

snpesnpe · **Joined:** Sat Jun 12, 2004 4:49 pm **Posts:** 915

then

Code:

if (yourObject!=null && session.get(YourClass.class,yourObject) == null)
  session.save(object);
else
  session.merge(object);

creating query for composite id is pain

snpesnpe · **Joined:** Sat Jun 12, 2004 4:49 pm **Posts:** 915

really

Code:

if (yourObject!=null) {
  if (session.get(YourClass.class,yourObject) == null)
    session.save(object);
  else
    session.merge(object);
}

hhuber · **Posted:** Fri Nov 18, 2005 4:40 am

snpesnpe wrote:

or simple call

Code:

try {
  session.load(YourObject.class, yourObject);
  exists=true;
} catch (HibernateException e) {
  exists=false;
}

Why not use get?
Then you can check for null instead of having to catch an exception.

hhuber · **Posted:** Fri Nov 18, 2005 5:32 am

hhuber wrote:

snpesnpe wrote:

or simple call

Code:

try {
  session.load(YourObject.class, yourObject);
  exists=true;
} catch (HibernateException e) {
  exists=false;
}

Why not use get?
Then you can check for null instead of having to catch an exception.

Already answered by later posts.

Sorry,
Heinz