Hibernate version: 3.2.6

Mapping documents: annotation

Name and version of the database you are using: postgres 8


Hi everyone,

I'm mapping an existing dataBase to Hibernate and I have an issue with manyToOne or even OneToOne.

On the db schema, the joinColumn for all our relations are defined as NOT NULLABLE, so 0 (zero) set a relation to null.

How can I tell hibernate that 0 means there is no relation ? (because today hibernate tries to find the relation and return an empty object).

If I use "@NotFound(action = NotFoundAction.IGNORE)" it works but I loose integrity constraints.

I've seen Formula and Filter but I don't realy know which one to use.

Thanks

This question comes up from time to time in the Hibernate forums.

According to Gavin King, one of the men behind Hibernate, the way to do this is to map 0 to null is to write a UserType that transforms 0 to null, and use that custom UserType as the identified type. Hibernate will not create a schema with default values, so in this case, you're on your own.

Another neat Hibernate trick is to use the nullif function in HQL. It's slick:

from Clazz c where nullif(c.cat, 0) is null

If both expressions are equal, null is returned, otherwise the first expression is returned, as you would expect. This simply helps out in the coding for the null or zero values.

This was discussed by men much smarter and better looking than me in the following thread:

http://forum.hibernate.org/viewtopic.php?t=945594

I'm also maintaining a list of suggestions and ideas on the topic on my blog:

http://hibernate3tutorials.blogspot.com/2008/07/how-to-map-integer-column-value-of-0.html

Good luck!

Hi Cameron,

Thanks for you quick response.

I think I'll start using "not-found="ignore".

I might also spend time writing a generic UsertType since all the relations I have are using the same "not nullable" join column.

Cheers,
Sebastien

Sorry, error while posting !

What about using Formula ?

Would that be an alternative ?