Hello, Hibernate users,

I'm using the following...

Hibernate version: 3.2.6
Database: MySQL Server 5.0.51a

..and I'm having a problem with a bidirectional one-to-one relationship. It exists between my entities "Client" and "Document".

I've written the mapping of the relationship according to "Hibernate in Action" and these are the important lines:

(In Client.hbm.xml):


(In Document.hbm.xml):


I'll describe shortly what I'm trying to do and what causes a problem:
- First I fetch the right Client object from the db.
- Then a method checks if that Client had any old Documents saved and if so removes them (it should only be one). - This works.
- Then a new Document is created and saved to the db, using the reference to that Client.
- After this I set the docRef property of Client to point to the new Document, which also works.

What doesn't work is this: When I check the db after program execution the Client reference of the newly saved Document is NULL.

I tried to add a call to session.update for the new Document but that didn't help.

Does anyone have an idea why this is happening?

I can post more information about the tables in the db later if needed.

I just really need some help 'cause I've tried lots of ways to solve the problem myself but I'm not getting anywhere.

Thanks in advance!

/Ylva

You've defined a foreign key relationship from Client to Document. At the schema level it means the Client table has the ID of the Document as a foreign key but there's no Client ID column in the Document table. If you use hibernate to generate the schema from your mapping files you'll see this. That's why the client ref is null in your pre-existing schema.

Thanks for your reply, Mike!

Yes, there is actually a Client ID column in the Document table. The database schema existed before I started doing this application. In fact I created it by hand and I used it in the first version of this application which used JPA and not Hibernate. Everything worked then so there must be a way to make it work with Hibernate.

These are the relevant parts of the database schema:


(Some of the things including the extra FK Constraints must have been added by JPA since I didn't write them from the start.)

But just now I realized that I wanted the 'clientId' of Document to be NOT NULL so I changed that in the db schema (in case it would help solving my problem).
The new line (in the Document table) looks like this:


But that was obviously a bad idea because when I tried running the app. I got the SQLException "Field 'clientId' doesn't have a default value".
Is it not possible to set a Foreign Key field to 'NOT NULL'? (I'm running out of time. That's why I'm testing things without being sure about them.)

Anyway, the problem was there even before that little change and I still have no idea what to do about it. Please help me figure it out!

/Ylva

If you can you should drop the clientId column from document - you don't need it for the java to work. Without the clientId column you can still load a document object and navigate to the client in java (and vice versa).

If you need the clientId for some external reason you could use the many-to-one with unique=true in BOTH directions. However, if you do this you'll have to explicitly set the client in the document as well as the document in the client.

Obviously this won't work if the foreign key columns are not-null and the primary keys auto assigned. Hibernate will have to update the foreign keys of both doc and client _after_ the objects have been created and hence their IDs assigned.


(In Client.hbm.xml):


(In Document.hbm.xml):

THANK YOU, Mike!!

That 'many-to-one with unique constraint on both sides' did it! (When I'd changed back the 'NOT NULL' to 'default NULL' for clientId of course.)

I wanted to keep the clientId column since I'm using the same database with my other application and I didn't want to risk ruining that.

Now the whole application works, thanks to you! :-)
As you can see I've rated your latest answer 'helpful', which it was indeed. (I can see why you have so many credits..)

All the best to you!

/Ylva