Deleting orphans on many-to-one

frer · **Joined:** Wed Jul 14, 2004 11:51 am **Posts:** 43

Hibernate version: 3.2

Hello,

I have read in the documentation that it is not possible to delete orphans by cascade in many-to-one associations.

Is it because there is another way or is it simply not supported.

I work with detached objects. Therefore, if my parent has an association on a child like Person -> Email, and that I delete the email from a Person, I would like that email to be deleted in the database.

To do so, I would like to do:
person.setEmail(null);

When saving the person (which is a detached instance), it would delete the association from the database (which already works) but also the Email instance (which is obviously not the case today).

How can I do this with the detached objects?

Thanks,

Francois

frer · **Joined:** Wed Jul 14, 2004 11:51 am **Posts:** 43

By reading more and more I have finally figured out 2 things:

1- My subject is incorrect because what I am really trying to do is a one-to-one relationship. Unfortunately the documentation suggests to use a many-to-one association to "simulate" the unidirectional one-to-one association.

2- There doesn't seem to be a way (with hibernate mappings) to delete the orphans of any many-to-one or one-to-one association.

I have read many posts including these:
http://forum.hibernate.org/viewtopic.ph ... t=onetoone
http://forum.hibernate.org/viewtopic.ph ... e+property

I don't have a problem with using the many-to-one association to "simulate" the one-to-one but I would like to be able to delete the orphan of this type of association when nulling the association:

Code:

person.setEmail(null);
session.save(person);

should result in both the person and the phoneNumber to be deleted from the database

Worst case scenario if anybody has a workaround, it would be greatly appreciated.

batmat · **Posted:** Fri Dec 08, 2006 5:01 pm

It should work, but you must ensure that you break the relation in both directions :

and map the relationship with cascade="...,delete-orphan".

frer · **Joined:** Wed Jul 14, 2004 11:51 am **Posts:** 43

Hi,

I'm not sure I understand what you mean by "break the relation in both directions".

Ideally, in my example Email does not and should not know about Person. It should be a unidirectional association Person -> Email.

This being said, if this is the only workaround I'm willing to look into it. Here are my mappings. How would you go in changing them to delete the "Email orphans"?

Code:

   <class name="org.hibernate.bugs.orphandelete.entities.Person" table="PERSON"
      lazy="false" dynamic-update="true">

        <id name="id"
            column="ID"
            type="string"
            length="32">
            <generator class="uuid.hex"></generator>
        </id>

      <property name="name" type="string" update="true"
         insert="true">
         <column name="NAME" />
      </property>

      <many-to-one name="email"
         column="EMAIL"
         class="org.hibernate.bugs.orphandelete.entities.Email"
         cascade="all"
              outer-join="false" 
         update="true"
                        insert="true"
                        unique="true"/>
          </class>
   <class name="org.hibernate.bugs.orphandelete.entities.Email" 
         table="EMAIL"
         lazy="false" 
         dynamic-update="true">

        <id name="id"
            column="ID"
            type="string"
            length="32">
            <generator class="uuid.hex"></generator>
        </id>


      <property name="email" 
              type="string" 
              update="true"
              insert="true">
         <column name="EMAIL" />
      </property>
   </class>

It is important to note that it is not possible to set "delete-orphan" on a many-to-one or a one-to one association.

Thanks,

François

frer · **Joined:** Wed Jul 14, 2004 11:51 am **Posts:** 43

Any ideas anyone?

batmat · **Posted:** Fri Dec 22, 2006 5:57 pm

<many-to-one> is rarely mapped with cascade="all" because it simply rarely makes sense. For example, it would mean that deleting one particular child would imply deleting its parent, which could have other children?!

On <one-to-one> I can't why you would map it with a cascading relation. But IMO, it would simply imply calling delete() on the item you want to be deleted.

Then, in fact, as said in the ref doc, unidirectional mappings are less easily "questionnable" by OR tool. So mapping if possible a bidirectional relation would certainly simplify your case. If you don't want to allow your users to see one of the side, just put the getter/setter protected on that side: this way your public contract will stay the same, and Hibernate will be able to use the other side information.