hi,
I am looking for help writing and using a custom Id Generator to generate compound primary keys.
I have checked the javadoc:(http://www.hibernate.org/hib_docs/annotations/api/) for org.hibernate.mapping.IdGenerator but it's not obvious how one would go about using this. Also I can't find a good link from Google or in the Hibernate book I am reading (Gavin King, Manning).

Does anybody have a good link giving an example of writing a custom Id Generator for generating compound primary keys.

Kind Regards

It's not possible to write id generator for composite keys.
See http://www.hibernate.org/hib_docs/v3/re ... ompositeid


In fact, it doesn't make sense to have generated composite keys: composite keys should be business manually assigned keys. Else when generated, it would be a lot more simple to define a simple column for the generated unique identifier.

Fair point. But I am trying to integrate with legacy database, a requirement is to still use composite keys and to to only assign them before the commit. The only way to do is to make the application code do it every time, this is cumbersome and bloats out the application code.

Comments appreciated.

As it's not possible to define generator for composite ids, maybe one solution could to define an Interceptor for this: you would intercept beforeSave() if (yourInstance instanceof YourClassWhichHasCompositeId) or something like this and call your special processing before calling the real save.

But please note I've no idea if this method would have some potential risk. Maybe it'd better than nothing?

I have tried doing something like what you say using the interceptor
method onSave(), the problem is that before the Hibernate framework fires the onSave event it checks to see if the entity has a primary key, if not it will throw an exception.

The same happens if you use the prePersist method.

One way around this would be to assign the Entity a POJO key a default key and then check for this, however at this stage things are getting a bit messy, and I am wondering there must be a cleaner approach.