Okay, having conquered the first newbie hurdle of LazyInitializationException, now I am faced with the second-most-common issue: NonUniqueObjectException in a cascade saveOrUpdate.

I have a Submission table, that contains many child Product records, and each Product contains many ProductFiles.

In my app, I load a Submission from the database using Hibernate, then populate it's children and grandchildren with Products and ProductFiles created at run-time, then attempt to saveOrUpdate the Submission. All my hbm.xml mappings have default-cascade="save-update", so Hibernate attempts to insert the new Products and ProductFiles (or at least it should).

At this point, I receive a "NonUniqueObjectException: a different object with the same identifier value was already associated with the session: [com.testProject.entities.ProductFile#0]".

I should note that the ProductFile entity's identifier is an Integer value, with a default (unsaved) value of zero. So here, it looks as though Hibernate is seeing a bunch of ProductFiles with the same ID (zero, since they are all unsaved), and is freaking out.

So how can I tell the Hibernate Engine that these objects are unsaved, and therefore not "identical"?

A little digging has uncovered that my hbm.xml files, which were generated by the mysterious, undocumented voodoo of the ANT hbm2hbmxml task, contain a <generator class="assigned"> for every class. I'll change this to "native", and see if that makes a difference...


[drum roll...]

Hmm. Nope. Now I'm getting "org.hibernate.id.IdentifierGenerationException: ids for this class must be manually assigned before calling save()".

So how can I tell Hibernate that these IDs will be generated by the Database engine (in this case a MySQL auto-incremented field)??

UPDATE: Okay, got it! I'll use <generator class="identity"/>

So I got all that working now, but I'm still getting a NonUniqueObjectException for something else, now.

Each Product has a child ProductType. So for each ew Product I create (and I'm creating several at once), I get an existing product type from the database, and associate it with the new product (Product.setProductType(Session.get(ProductType.class,3))). I'm making a separate call to Session.get() here, which may be loading multiple ProductType objects with the same ID(?)

The associated ProductType hasn't changed, so it's not dirty, so when I call session.save(Product), Hibernate shouldn't try to update the "child" productType, correct? And yet I'm getting "NonUniqueObjectException: a different object with the same identifier value was already associated with the session: [com.testproject.entities.ProductType#3]"

What am I doing wrong here? Why does Hibernate think the ProductType instance is dirty?