Many-to-many collection management

_guillaume · **Posted:** Tue Jun 10, 2008 5:55 am

Hibernate version: 3.1.3

Mapping documents for class Product :

<set name="types" table="PRODUCT_TYPES" >
<key column="PRODUCT_ID" />
<many-to-many class="Type" >
<column name="TYPE_ID"/>
</many-to-many>
</set>

Hi,

I tried to managed an association table with a "many-to-many set". The insert/update/delete operations don't work in all cases.

For example, if I try to do the following actions :

Code:

// begin transaction
Product prod =  getSessionFactory().getCurrentSession().load(Product .class, 1);
prod.getTypes().clear();
// end transaction

SQL generated : delete from PRODUCT_TYPES where PRODUCT_ID=?

=> Hibernate delete all the rows in PRODUCT_TYPES table for the my current product with which is ok!

But if I try to clear and add an element, it doesn't work properly. For example :

Code:

// assuming myType has been loaded in the same session and prod.getTypes() is not empty.

// begin transaction
Product prod =  getSessionFactory().getCurrentSession().load(Product .class, 1);
prod.getTypes().clear();

prod.getTypes().add(myType);
// end transaction

SQL generated :
delete from PRODUCT_TYPES where PRODUCT_ID=? and TYPE_ID=?
insert into PRODUCT_TYPES (PRODUCT_ID, TYPE_ID) values (?, ?)

=> Hibernate generate a delete/insert in PRODUCT_TYPES table for the type myType but does not delete the old association lines (that has been deleted by the clear method).

I should have the two sql statements :
delete from PRODUCT_TYPES where PRODUCT_ID=?
insert into PRODUCT_TYPES (PRODUCT_ID, TYPE_ID) values (?, ?)

I can understand that hibernate can't know if the set has been clear or not, so it doesn't generate a delete. I thought I could flush the session after calling clear method but it is not a very good practice I think.

Can I manage an association table only by using the set in my object or should I write some methods in my DAO to handle this case ?

Thanks,