Unidirectional one-to-many association

deltoura · **Joined:** Mon Sep 19, 2005 5:32 am **Posts:** 2

Hi,

I have a question about the Hibernate Reference Documentation version 3.0.5. In the Chapter 8. Association Mappings it says:

Quote:

A unidirectional one-to-many association on a foreign key is a very unusual case, and is not really recommended. [...] We think it's better to use a join table for this kind of association. [...] A unidirectional one-to-many association on a join table is much preferred.

I need to map such an association, and it seems more natural to me to use a foreign key than a join table.
Could someone explain why the documentation says not to do so?

Thanks,

Amélie

Hibernate version:
3.0.5

emmanuel · **Posted:** Mon Sep 19, 2005 1:59 pm

The join table keep your second table free of any "polluting" FK. If you want to use a join column, feel free.

deltoura · **Joined:** Mon Sep 19, 2005 5:32 am **Posts:** 2

Thanks for the answer.

I'm not sure the FK is so "polluting" in our case.
What about performance issues? Isn't a join table less efficient for performance than just a FK?

I think it would be useful if the reference documentation could explain the pros and cons of each of the options, instead of just saying it is "not recommended".

Amélie

emmanuel · **Posted:** Wed Sep 21, 2005 5:29 am

it requires an extra join, wich shouldn't be too costy.
If we put an explaination, we'll find a DBA who disagree with us, then we'll have to explain the explaination and so on ;-)

steep · **Joined:** Mon Jul 31, 2006 12:24 pm **Posts:** 1

Quote:

If we put an explaination, we'll find a DBA who disagree with us, then we'll have to explain the explaination and so on ;-)

Agree or disagree, the fact of the matter is that there is an opinion written into the documentation that causes the reader to wonder if there is some type of technical/performance reason for it being there. That statement sent the original poster, me, and probably countless others on a wild-goose chase.

It should be removed.

mellster · **Joined:** Fri Apr 15, 2005 7:52 pm **Posts:** 13

I agree with the previous comment. While migrating to annotations I spent many hours on this topic simply to find out that this is a totally debatable statement. People might get scared and needlessly try to update their whole schema to "comply" with that statement. Hibernate is an awesome product, but sometimes the docs are a bit too opinionated ;)