0..1 Mapping using a separate link table

StanAccy · **Joined:** Fri Sep 03, 2004 2:01 pm **Posts:** 51

Hibernate version:2.1.6

I have the following objects:

A (1..n) -- B (0..1)

I need to store A's value of B in a separate table (for data integrity - so that we can make use of non-null fields and Foreign Keys).

We need three tables:

A_TBL
====
ID PRIMARY KEY,
PROPERTY_ID

B_TBL
====
ID PRIMARY KEY

A_B_TBL
======
A_ID (FK)
B_ID (FK)
PROPERTY_ID (stored for business data integrity reason so we can add a unique constraint)

Many A's could reference the same B
One A can have zero or 1 B

What is the best way to map this?

StanAccy · **Joined:** Fri Sep 03, 2004 2:01 pm **Posts:** 51

I omitted that:

In A.java

is has a nullable property 'B'

I can map this using Collections - but is there a way to map 0..1 mapping like this using an association table?

Nick

StanAccy · **Joined:** Fri Sep 03, 2004 2:01 pm **Posts:** 51

Is there anyway to achieve this without having to make a separate A_B java class (and adding its associated mapping file) ?

This is a fairly common DB data integrity pattern for 0..1 relationships - if 2.1.6 doesnt support it directly, are there plans for H3 to provide this support?

emmanuel · **Posted:** Sat Nov 06, 2004 8:21 am

In H3 road map

Quote:

ability to map association tables as having one-to-many multiplicity at the object level

For now, put a private collection and do

Code:

getB() {
  return (B) myHiddenColl.get(0);
}

StanAccy · **Joined:** Fri Sep 03, 2004 2:01 pm **Posts:** 51

Thanks. That's what I came up with over the weekend.

With regards to the H3 roadmap - is there a list of features, and whether or not they are implemented yet? (Along with an estimate of when a beta is likely?)

Thanks again

Nick

christian · **Posted:** Mon Nov 08, 2004 10:17 am

Uhm, that is what is _in_ the road map actually :)

StanAccy · **Joined:** Fri Sep 03, 2004 2:01 pm **Posts:** 51

Thanks Christian - I sorta understand what the roadmap is - I was asking where it was online {:-)

Nick

christian · **Posted:** Mon Nov 08, 2004 10:30 am

Its in the main navigation on the left side of hibernate.org ;)

StanAccy · **Joined:** Fri Sep 03, 2004 2:01 pm **Posts:** 51

So it is {:-) Any more info on the first beta release date?

christian · **Posted:** Mon Nov 08, 2004 10:35 am

I think "this year" is a good enough guess at this point, some issues are still open and in the process of being resolved.