Hello forumers,

A few months ago I stumbled over what I consider a bug in the translation of javax.persistence Annotations to the configuration model used by the hibernate core. Briefly put, under very specific circumstances the "optional"-Attribute of a @OneToOne or @ManyToOne is lost in translation, causing Hibernate to proxy the remote end of the association even if no associated object exists.

I reported that. Emanuel Bernard closed the bug, stating that he disagrees with my understanding of the semantics of "optional", and gave a work-around. I pointed out why the work around doesn't work reliably for us, but apparently nobody reads comments on a closed bug report ...

So I ask here: How can I reliably and non-redundantly specify that a @OneToOne should be nullable?

Hi,

Have you tried to map your optional one-to-one association via a join table. I believe this is the recommended way in this case. There are two ways of achieving this. Either via with a @JoinTable or with @SecondaryTable.

The former could look like this:


The book "Java Persistence with Hibernate" covers this type of mapping in more detail.

--Hardy

We have to share the database with a legacy application; we therefore can't change the schema. (==> no join table ...)

I don't get how @SecondaryTable would help with an optional association.

I have looked in the book, and didn't find anything applicable. I might have missed something, which chapter are you referring to?

Hi,

I am referring to chapter 7.1.3 - the Person and Desk example.

Ah, this is for the join table approach. Our association is only nullable in one direction, so the purist mapping would be a nullable foreign key column (chapter 7.1.2). But that's a moot point, because we can not change our schema from the shared primary key variant (chapter 7.1.1).