Problem with saving entites with non optional associations

plusplus · **Joined:** Fri Dec 29, 2006 12:20 pm **Posts:** 8

Hi all

I'm using Hibernate 3.02 with annotations. I'm trying to map an association between two entities. The Problem arises when both sides of the association are mandatory. So each entity needs a constraint not to let the other side to be null.

So I cannot save either of the entities, cause each entity needs the otherone.

Help please.

kochcp · **Posted:** Tue May 29, 2007 11:34 am

Hibernate Validator will check if a field is null and throw an exception if it is.

But, I think hibernate will do that automatically (without Hibernate Validator) by setting not-null="true" on that field.

orr, you could do it manually like this

Code:

ClassA {

private ClassB classb;

public void setClassb(ClassB classb) {
this.classb = classb;
if classb.getClassa == null)
throw Exception

}

}

or write your own Listener to check the classes before save and update

plusplus · **Joined:** Fri Dec 29, 2006 12:20 pm **Posts:** 8

Thanks for help, but that was not actually the problem. I'm using MySQL database and should tell the database not to check the foreign key constraints for saving objects just for some time.

suppose I have A and B. B should have an A and A also should have a B. Suppose having this code:

Code:

sf.getCurrentSession().beginTransaction();
A a = new A();
B b = new B();
a.setB(b);
b.setA(a);

sf.getCurrentSession().save(a);
sf.getCurrentSession().save(b);

sf.getCurrentSession().commit();

This code will throw exception, because saving a will need a valid b, but b itself needs an a to be saved. Database will not allow me to save a without any b. Because of foreign key constraints.

This loop will make the problem.
I think this is not hibernate's problem, I should tell the database to do this, but by hibernate's help.

any idea?

kochcp · **Posted:** Tue May 29, 2007 12:32 pm

Set up your mapping files correctly then.

Hibernate can insert both of those classes into their tables and use any auto-generated values from the database in any foreign key fields with only one call to save.

If your database has must exist on both ends then you should probably fix that first.

plusplus · **Joined:** Fri Dec 29, 2006 12:20 pm **Posts:** 8

I have a constraint of type "must exist" on both ends and that is my problem. I want mysql to forget the foreign key constraints just for a moment and let me save my objects.

How can I do that? You mean Hibernate will automatically do this for me and there is no need to tell anything to my MySQL?

kochcp · **Posted:** Tue May 29, 2007 12:47 pm

you should have it mapped that:

Code:

<class name="classA"
>

...

<name="many-to-one"
 class="com.package.ClassB"
 not-null="true"
 >
<column name ="foreignkey" />

</many-to-one>

</class>

on both ends. (or one-to-one) And if they reference auto-generated values hibernate will pick those up and use them for the inserts.

if one-to-one there is even a foreign-key attribute you can set

plusplus · **Joined:** Fri Dec 29, 2006 12:20 pm **Posts:** 8

I made making a mistake. Thanks again. It's correct now.