I have one parent with many children using the save-update cascade option children. Saving the transient parent with its transient children works but no foreign key from the child back to the parent was being stored. I assumed I had to call child.setParent( parent ) on each child to fix the problem. I tried that and got the following error:

"object references an unsaved transient instance - save the transient instance before flushing: foo.bar.Parent"

Do I need to save the parent first and add the children later?

Anthony posted this response to a recent question related to mine. I am doing the child.setParent( parent ) and parent.addChild( child ) thing but outside of a session. I expect hibernate to persist the parent first followed with the children but instead I get the "unsaved transient" error.

*********************

Transaction trx = session.beginTransaction();

Parent stephen = new Parent();
stephen.setName("Stephen Earl");
session.save(stephen);

Child simon = new Child();
simon.setName("Simon Earl");
stephen.addChild(simon);
simon.setParent(stephen);

trx.commit();

either do

befor commiting

od specify cascade="save-update".

Referende manual chapter 16 describes this in detail.

HTH
Ernst

Understood but that was a quote from a working example and I believe they were using save-update. I am using save-update as you suggest so all's well on that front.

My question is whether you can create a new parent with new children and save the tree with session.save( parent ) or whether the parent must fist be persisted.

I think my question is going off in the weeds so here is a course correction:

Persisting a populated parent works. Examining the database reveals the child records have a null parent reference. This is because the parent was not set for each item so the back-reference is missing.

To fix the problem I call child.setParent( parent ) on each child. The problem is the parent is transient (not unattached but rather entirely new) and so are all of the child objects. This tree is created and used long before it is stored in the database. That is how the application is designed.

Now, when the time comes to persist it I get the reference to an unsaved object complaint. This begs the question, can a tree be saved in one fell swoop or not? Must the parent be saved first if the children have a back reference to the parent?

Thx

AFAIK the parent must be saved first.

If you speciefy cascade="save-update" that's all you have to do, else save the children as well.

HTH
Ernst

That would mean you could not create a tree and save it without some code gymnastics. Customer creates an order and adds a pizza with toppings. The order is then sent over to the persistence manager where the elaborate dance is implemented: remove pizza, remove toppings, persist order, persist pizza, update pizza with toppings, update order with pizza. Yikes!

Here's a solution. Pretty simple and only unnatural in that you can't use the back references from, say, the pizza to its order. Not a big deal really.

// Create a POJO order independent of storage. Just beware that the
// pizza.getOrder() will be null and topping.getPizza() will be null.

Order create()
{
Order order = new Order();
Pizza pizza = new Pizza();
Topping cheese = new Mozarrella();
Topping meat = new Pepperoni();

pizza.add( cheese );
pizza.add( meat );
order.add(pizza);

return order;
}

// Save the order in two steps: without links then with links. Otherwise
// Hibernate whines about transient objects being referenced.

store( order )
{
session.save( order );

cheese.setPizza( pizza );
meat.setPizza( pizza );
pizza.setOrder( order );
storageManager.store( order );

session.update( order );
}

Mmmm ... I guess you didn't unerstand how to work with persistent objects in hibernate.

Read chapter 4 of Hibernate in Action. After that have a look at chapter 16 of the reference manual to understand parent/child relations.

HTH
Ernst

I would say that I understood those secions entirely but that it failed in a way that is not described in HIA or the reference manual. In fact you do not have to store the parent first and that much is documented. My question was slightly more specific. If a child has a parent reference and both are transient to you have to store the parent first? In that case, and only that case, the answer appears to be affirmative but I am still not sure. I thought perhaps there was a way that Hibernate could deal with this circular reference since it's entirely detectable and have still not received a clear answer on whether that's possible. Pretty much down with how hibernate is working otherwise.

Thanks.