I'm busy adapting Hibernate to an old DB Schema. The DB is and will be used by a number of legacy applications which I cannot change.

The Problem I'm facing is, that sometimes 0 is used to express NULL semantics and sometimes a real NULL is used for the same column. I'd like to make this transparent to my new java business logic.

Is it a good idea to create a user type with a nullSafeGet which returns a java null in case it reads 0 or NULL from the DB?

I think this works fine, if the user type is used for an ordinary property.
What happens if the column is part of a foreign key? My guess is that it's still using the nullSafeGet of the user type, which means it's ok.
Does is also work wiht HQL? I don't think so, how can Hibernate now that an should be expressed as an

Are my thoughts correct? Is there a (better?) way to do that and maybe have the HQL case working as well?

Best Regards
Ernst



Hibernate version:
2.1.4

You have to do things like that in HQL yourself - you should know your DB schema. Besides, id=null won't work anyway, you have to use "id is null"

What about the ordinary property and the foreign key case? Do they work as expected?

Best Regards
Ernst

You mean thinks like having a "not-set" foreign key represented as 0 and not as null? That will not work. Hibernate requires a minimally intact relational schema.

Does this mean the only way to get this relations working with Hibernate is to convince the dba and the other application owners to cleanup their code/databases?

Mmm ... that's bad news.

Thanks for you help anyway.
Ernst