I have a many-to-one relationship defined between 2 classes (MusicFile and Category). The idea is that each MusicFile object can have an associated Category. That means that 2 different MusicFile objects can have the same Category.

I have the relationship defined as follows:


Now, I try to add the following:
MusicFile1 (id=1, name="file1", category="cat1")
MusicFile2 (id=2, name="file2", category="cat1")

Since I have cascade="all" specified the Category object is added when I do a session.save() on the MusicFile. It works for MusicFile1, but MusicFile2 throws an SQLException because "cat1" already exists.

My question is - how do I get around this with Hibernate? Or do I have to turn off cascading and add the Categories before I add the MusicFiles? I thought that there might be some way to say for Category that if it already existed then don't add it.

Any help is appreciated.

are you doing a setCategory(instanceOfCat) or are you doing setCategoryId(catId)

maybe if you do the former, it will not try to create a new object. I'm too new to be sure, but i figured i'd throw that out there.

Here is the code snippet from my simple test program. To directly answer your question I am setting via setCategory( CategoryInstance).

i think you want to do this:

// MusicFile and Category
Category cat = new Category();
sess.load(cat,"MyFavorites");

MusicFile musicFile = new MusicFile();
musicFile.setCategory( cat );

Not sure why I would want to do that? The category I am adding may or may not exist. Shouldn't the hibernate code have a way to handle this? Especially since I want to put this into an automated loop and read files in from the filesystem and use this code.

Additionally, even if I do the session.load(cat) won't hibernate still try and add it?

I don't want to sound rude here, but as far as I can tell, hibernate will not do anything magical for you. Its the glue between your object and the database. It seems to have been designed to be fast, and not so much to figure out your specific business logic. (DISCLAIMER.. I'm pretty new to hibernate, so I'm no expert)

It seems to me that you will have to do your own lookup to figure out if the category already exists.

If it were my code, i would do this (roughly) ...

java.util.List allcat = sess.find("select cat from Category cat");

while (true) {

Category c = new Category();
c.setName(arrayofvars[i]);
int where = allcat.indexOf(c);
if (where >=0)
{ c = allcat.get(where);}
else
{ sess.save(c);}

MusicFile musicFile = new MusicFile();
musicFile.setCategory( cat );

sess.save(musicFile);

}
sess.flush();
tx.commit();

maybe hibernate team has a better method... not sure... hope it helps