Hibernate version: 3.1

Hello

This is a general question.

I have a User object and some other objects such as Comment, BlogEntry, ForumPost etc. All of the later objects keep a reference to a single User object, which represents the creator.
I've mapped this reference to the creator using a many-to-one hibernate relation pointing to the unique id of the user. Everything works well, until I delete a User (e.g user with id 23) who has already created some Comment, BlogEntry etc object. When I try to get any of those objects, which still point to user 23, I get:

org.hibernate.ObjectNotFoundException: No row with the given identifier exists: [User#23]

I would like to get a null reference for User inside my Comment/BlogEntry object instead of this exception.
What should I do?

Should I 'nullify' all references to user 23 before deleting him? Should I do that myself (using a database trigger, on the java level) or is there a more elegant way so hibernate can handle this logic for me?

Note that I do not want on delete cascade because deleting user 23 would delete his comments/entries as well.

thanks

You can create a foreign key in your children tables (comment, post etc.) and set it to 'on delete set null'. This way, when a user is deleted, user_id column is set to null.

You may face another problem : if Hibernate has cached items belonging to this user, Hibernate will be aware that they have be updated (user set to null). In this case Hibernate will query the DB for this use and will report an exception (since it as been deleted).

If you want to avoid this, my advice is to nullify all user fields at Java level.

thanks for your reply

This 'on delete set null' thing, how do I do it? On the DB level? With a trigger?

On the DB level, when you create the FK.

Kind Regards,

Just to let you know that what I wanted was the not-found="ignore" property on the <many-to-one relation.

thanks