Help ! ;-)

I want to design a very simple mapping scenario with Hibernate and I get some pb.

I have 2 tables with a 0-1 association

Item --> ItemDetail

Here are my tables :

Item
--------------------------
ITEM_ID Number()
MyText Varchar()

ItemDetail
----------------------------
ITEMD_ID Number()
MyDetails Varchar()
ITEM_ID FK on ITEM_ID Table

My POJOs:
Item {
getID();
String getMyText();
<b> ItemDetail get/setItemDetail();</b>
}

ItemDetail {
getID();
String get/setMyDetails();
}

By default hibernate requires that you create an FK column on the Parent class. I don't want to do this because I don't want to deal with null FK column issue (the associated object ItemDetail can be null) in Item table.

Is it possible to move this FK column in the ItemDetail table and only indicate in the hibernate mapping file that the FK column is not in Item ?

Please I prefer not using bidirectionnal association or complex scenarios...

Thanks a lot.

Rabby

I think I didn't understand what you were saying about "nulls" and "FKs", but what you are looking for might be this:

Hello Christian (thanks for the reply),
I prefer not inserting a FK_ITEM_DETAIL_ID column in my ITEM table because it is a 1,0 association and I will deal with such datas in my tables :

ITEM Detail FK_ITEM_DETAIL_ID
1 "My Item" null
2 "My Other Item" null
3 "My OO OTher Item" 1

ITEM_DETAIL
1 "My Item Detail"

You see what I mean ? This is better to have a FK in the ITEM_DETAIL table like following :

ITEM Detail FK_ITEM_DETAIL_ID
1 "My Item"
2 "My Other Item"
3 "My OO OTher Item"

ITEM_DETAIL FK_ITEM_ID
1 "My Item Detail" 1

How can I do that ?

Your data and my mapping work very well.

I have certainly missed something. I have cut and paste your mapping file :


Here is my POJO :


Here is the error which is normal, itemDetail is not mapped with a Foreign key in Item class but in ItemDetail class...

[HibernateUtil] closeSession()
<25 2004 15 h 02 CEST> <Error> <HTTP> <BEA-101017> <[ServletContext(id=34547968,name=webapp,context-path=/webap
Root cause of ServletException.
net.sf.hibernate.HibernateException: unmapped property: itemDetail
at net.sf.hibernate.persister.AbstractEntityPersister.getPropertyValue(Ljava.lang.Object;Ljava.lang.String;)

Does I missed something ?[/code]

Yes, you are not using the mapping you have shown. Please re-read the Parent/Child relationship chapter and other parts of the documentation. Your problem is trivial, but you got confused by "moving the FK over there because of NOT NULL", which doesn't make much sense...

Christian,
I have read many times the documentation (i have bought hibernate in action ebook) on Parent/Child topic. It is always specified that the foreign key should be placed in the Parent class (in my case Item). I don't understand why this is a requirement...

You are right that not-null constraint doesn't make sens here since I will always have a valid FK in ItemDetail table. My the problem is that I can't have any foreign key in my parent class.

So, how can i handle such data ? Why is it so trivial ?

Again, step by step: Why can't you have a FK_DETAIL_ID column in ITEM? The reason you gave "because of nullable" doesn't make sense. It surely can be NULL, which means that an ITEM doesn't have a DETAIL.

Because the existing schema is already designed like this and we want to avoid to update the existing data just because hibernate can't handle a navigation parent/child with the foreign key in the child class (which is the traditionnal design adopted by our DBA to minimize null columns).

Imagine that you have more than 1.000.000 records in the ITEM table having one ITEM_DETAIL.
With your solution, I will have more that 999.999 records set to null in ITEM table while our actual schema have just 1 record in the ITEM_DETAIL table with a non-null FK pointing on ITEM.

Very bad.

Anyway, thanks for your answers...

If you would explain yourself better, you would be less frustrated with the answers you receive.

Now, it just so happens that I can guess what you want. Though its pretty hard, given the way you've communicated it.

What you need is <one-to-one name=".." property-ref="..."/>. You will find this documented in the Hibernate manual.

Now, in Hibernate 2.1 there were some performance problems associated with this kind of mapping. These are fixed in the just-released Hibernate 3.0 alpha.

In future, please spend much more effort on proper explanations. TIA

Gavin,
If each time I ask (this is the first and the last time) a question, I should pay the price of your arrogance, you should seriously consider not funding a commercial company (with Jboss or others). If I were a customer (and I am, I bought your book and try tro promote Hibernate in one of the biggest french company), I would leave you right after such a response.

I have posted the mapping file and the POJO code. What the hell can I do more than that ? And I already spend much effort trying to post in english which is not my mother language.

myrabbit,

I completly can't understand Your irritation. I can't see anything bad in Gavin's answer. Reading Your question I did it understand after fourth post (earlier You even didn't mentioned that You don't want to change Your schema). Furthermore this is a free support forum and some people do their best to help other for free. If you want a more sophisticated support consider buing it (it's not so expensive). Just my $.02.

Artur

Hello Artur,
Please re-read my post and you will see that I repeated twice that I don't want (and can't) to change my schema...

1st post

another one :



Don't know what to do more than that.

I am graceful about the free support (I have always thanked Christian) but disapointed about the last Gavin's response (and the lack of clean support of 1,0 association in Hibernate 2)

Anyway, let's forget it. Im also not obliged to use hibernate.

[/quote]

Account banned.