I wonder if it is possible to create a one-to-many mapping without an attribute linking back.

In Java it is common to use containers of objects. The objects know nothing of the object holding the container. I know that the DB table needs a column to link from B to A. Do I need to do that in my Java classes too? Is it possible to map the following class without adding a A attribute to my Java class?



Regards
Haug

If you don't have an A attribute on your B Object, how will you insert a new B and identify it as belonging to A ?

This is simple, the OR mapper adds a reference column to the B-table (b_Id) without adding an attribute to the B-object. The get operation selects all from b-table with b_Id = a_Id. The set operation could be implemented similar.

Your question answers my original question, Hibernate forces the relational model to the object model. The object model uses a uni directional one-to-many relationship. The relational model doesn't have such a thing directly, you have to "emulate" it. And Hibernate doesn't do that. That's the answer to my original question.

The mapping you propose is legal and actually works. I just modified one of my small test programs to match that mapping and was able to both save and retreive data. Hibernate has no objections to uni-directional associations though I seem to remember a comment in the manual that in SOME cases they might not perform well.

Can you please post some mor information how this mapping is done?

I tried doing it but was unable to insert into child table! how did u do that?/

Uni-directional and bi-directional is possible (though in most cases your better off using bi-directional -- see manual for explanation).

In a uni-directional mapping the parent mapping of the set is the same as bi other than inverse="false" (or leave it out) attribute. The child will not have the many-to-one mapping. In both cases the DDL is the same.

I have had this issue while deleting. I tried to delete the parent with a mapping on the parent class link to the child as
<set
name="childProps"
lazy="true"
inverse="true"
cascade="all"
>
<key>
<column name="PARENT_ID" />
</key>
<one-to-many
class="ChildClass"
/>
</set>

and it tries to delete from the parent without deleting the children which causes the database to throw a child record found error because the child not being deleted.

Thanks for any help!!

Surya

I'm not sure, but maybe cascade="all,delete-orphans" might help.
The question that arises is whether a child object that is not in the set any more should be deleted. I don't think that Hibernate does that per default.



hth,
Heinz
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