Managing entities - EJB 3 in Action - page 412

Cascading remove operations
Just as with merging and persisting entities, you must set the cascade element of a relation-
ship annotation to either ALL or REMOVE for related entities to be removed with the one
passed to the remove method. For example, you can specify that the BillingInfo en-
tity related to a Bidder be removed with the owning Bidder entity as follows:
@Entity
public class Bidder {
@OneToOne(cascade=CascadeType.REMOVE)
public BillingInfo setBillingInfo() {
From a common usage perspective, this setup makes perfect sense. There's no reason for
a BillingInfo entity to hang around if the enclosing Bidder entity it's related to is
removed. When it comes down to it, the business domain determines if deletes should be
cascaded. In general, you might find that the only relationship types where cascading re-
moval makes sense are one-to-one and one-to-many. You should be careful when using the
cascade delete because the related entity you're cascading the delete to may be related to
other entities you don't know about. For example, assume there's a one-to-many relation-
ship between the Seller and Item entities and you're using cascade delete to remove a
Seller and its related Items . Remember the fact that other entities such as Category
also hold references to the Items you're deleting, and those relationships would become
meaningless!
Handling relationships
If your intent was really to cascade-delete the Item s associated with the Seller , you
should iterate over all instances of Category that reference the deleted Item s and re-
move the relationships first, as follows:
List<Category> categories = getAllCategories();
List<Item> items = seller.getItems();
for (Item item: items) {
for (Category category: categories) {
category.getItems().remove(item);
}
}
entityManager.remove(seller);