Newbie: implementing cascading delete for linked entities?

davout_uk · **Joined:** Tue Apr 10, 2007 10:02 am **Posts:** 56

I have a question about the validity of using cascading delete Hibernate definitions.

My example involves two entities 'Customer' and 'Order'. My Hibernate design envisages these as being two discrete hibernate mappings. Although a customer is associated with an order (the order table will include a 'customer ID' foreign key column), the orders are not defined at the same or place as customers are created and maintained.

Hence...

Code:

public class Customer {
   private int CustomerID;
   private String CustomerName;
   ...
   ...
}

public class Order {
   private int OrderID;
   private String OrderNumber;
   private double OrderAmount;
   private int CustomerID;
   ...
   ...
}

As the Customer class is potentially quite large neither does it make sense for the customer class to be added as a property to the Order class.
Thus, I have two separate Hibernate mappings for one each class, with no one-to-many association included in the Customer mapping.

The downside of this approach is that I lose the cascading delete facility by having the association between customer and order.

To address this is it valid to create a second class that descends from 'Customer' with its own Hibernate mapping that overlays the same customer table. THis new mapping would be used solely as a vehicle for delete operations?

Like..

Code:

public class CustomerPlus extends Customer {
   private Set<Order> fOrders = new HashSet<Order>()
   ...
   ...
}

In the Hibernate mapping for 'CustomerPlus' I'd add a lazy load one to many association with a cascading delete. For all customer 'delete' operations in the DAO tier Java class I'd load the CustomerPlus class and use it as a vehicle to enact deletion of the related orders.

Does this make sense? Thoughts?

lester · **Posted:** Mon Jul 09, 2007 8:59 am

Yes, it's reasonable approach. You can create separate CustomerLightWeight class with its own mapping and use it in one-to-many association and for delete operations. CustomerLightWeight class doesn't have to be subclass of Customer and vice versa. CustomerLightWeight and Customer must be mapped as different entities.

lester · **Posted:** Mon Jul 09, 2007 8:59 am

Quote:

Yes, it's reasonable approach. You can create separate CustomerLightWeight class with its own mapping and use it in one-to-many association and for delete operations. CustomerLightWeight class doesn't have to be subclass of Customer and vice versa. CustomerLightWeight and Customer must be mapped as different entities.

Sorry for the second post of the same message, i've had problems with connection and with posting. Could moderator delete second post, please? I can't do it via interface.

davout_uk · **Joined:** Tue Apr 10, 2007 10:02 am **Posts:** 56

Can I setup my 'CustomerPlus' hibernate mapping as a subclass in the same mapping file, or does it have to be in a sep[arate mapping file?

lester · **Posted:** Tue Jul 10, 2007 8:03 am

I think, you had better map CustomerLightWeight (or CustomerPlus) and Customer as completely different entities, otherwise you'd need to introduce discriminator column or additional table in your schema (see "Mapping class inheritance" in Hibernate). You could, however, map two different entities in the same mapping file (if they belong to the same db schema).