Hi.

I'm pretty sure I'm doing something wrong here but I couldn't figure it out until this point. I'm using Hibernate 2.1.2 on PostgreSQL 7.4.1.

I have something like a tree structure in the following table:

create table entity (
id integer not null,
name varchar(40) not null,
parent_id integer,
primary key id
);
alter table entity add constraint entity_entity_fk foreign key (parent_id) references entity;

This will restrict deletion on "entities" that have children, right?

In the mapping file, I have the following declarations:

<many-to-one name="parent" class="eg.Entity" column="parent_id"
insert="false" update="false" outer-join="false"/>
<set name="children" lazy="true" table="entity">
<key column="parent_id"/>
<one-to-many class="eg.Entity"/>
</set>

The class is fine, mapping is fine, table is fine. It works fine except for a small problem:
when I try to delete an entity that have children, I was waiting a JDBCException, because of
the constraint I created in database, but it doesn't occurs.

Instead, Hibernate sets all children's parent_id to null and deletes the parent, so there's
no referential integrity violation. That's my problem, because I can't delete an entity that have
children in my application.

I know I can check in my code if an entity has children before trying to delete it, but I want to
use database referential integrity in order to avoid unecessary calls to the database.

What am I doing wrong here? Any alternatives?

iran

try inverse="true" cascade="all-delete-orphan"
in your collection

not responsible for missing data!

Thanks for the quick reply.

Unfortunately it didn't work.

Hibernate still keep setting all child's parent_id fields to null before delete the parent.

I'm looking for a way to avoid this behaviour, if such way does exists, of course.

Any other sugestions?

cascade="none" say to not touch this association during cascades, so that will do what you specify here.

cascade="all-delete-orphan" should work, by actually deleting the children instead of updating their FKs to null. Do you have both sides of the association mapped?

Yes, I have both sides mapped, since they are the same class.

Here is my complete mapping:



Is this kind of mapping nonsense?

My "entity" can have a "parent entity" (or no parent) of type eg.Entity. In addition it can have a set of "child entities" that are of type eg.Entity too. Kind of a circular reference.

As I wrote before, I have a constraint in my database that prevents deletion on entities that have children, better saying, prevents deletion on entities whose ids are used by other entities in parent_id.

It works fine, but Hibernate is setting entity.parent_id to null on entities that have parent_id equals to the entity's id I want to delete, and it is done before perform deletion. Thats the behaviour I would like to avoid, because I wanna catch the JDBCException generated from the database by my constraint.

Is that possible?

Thanx.

Nope, I use the same exact pattern in some of my apps. Its called the "Composite Pattern". Check out http://hibernate.org/86.html for details on implementing this in Hibernate mappings. Pay specific attention to the "inverse" and "cascade" values...

Yeah!!! It worked Steve.

Thanks a lot.

However I didn't understand the effect of inverse="true" yet. But I will reread the documentation more carefully.

Thanks again.

Check out http://hibernate.org/155.html. Pretty thorough dicussion of the implications of inverse values in various scenarios.