Using orphan removal in Hibernate

Question

I am working in Spring-Hibernate application.My question is related to orphan removal as described below in the code.

@Entity
public class User {
    ...........
    @OneToMany(mappedBy = "user", orphanRemoval = true, cascade = CascadeType.ALL)
    List<UserRole> userRoles = new ArrayList<>();
    ..........
}

Considering the save/update User scenario. One way is to remove that child object from the list like user.getUserRoles().remove(userRole).
The other way could be like clearing the child list as user.getUserRoles().clear() and then adding it to the list whatever user roles are coming in the request. In this case, user roles not coming in the request will be deleted by orphan removal.

Which one is better and more correct?

Answer 1

Well, it depends upon the situation and the type of semantic you are using; see Collection performance for more information on different semantics and their performance tuning.

Well, in this case you are using list semantic for the one-to-many association, therefore suppose you have 20 elements in list then:

Option 1: you are removing 15 elements one by one and adding 1 elements in it then hibernate will issue 15 DELETE statements and one INSERT statement.

Option 2: you clear the whole list and add all 6 elements manually, this way only 6 INSERT statements will be issued and 1DELETE statement will be issued.

I will go with the option 2 if the collection is heavily modified see One shot delete for more details and I will go for option 1 if the list is not heavily modified.

Answer 2

Apart from your collection and number of instances on it, I think the first way (removing the child element from the list) is the most appropriate one, and that's exactly what orphanRemoval is designed for.

Because with orphanRemoval all that you need to do is to remove the child from the relation table and this child(record) will be automatically removed from its original table.

Because if you take a look at Orphan Removal in Relationships documentation you will see that:

When a target entity in one-to-one or one-to-many relationship is removed from the relationship, it is often desirable to cascade the remove operation to the target entity. Such target entities are considered “orphans,” and the orphanRemoval attribute can be used to specify that orphaned entities should be removed.

So I think the best way is to let Hibernate do its job automatically, rather than doing it manually, after all that's the first purpose of using orphanRemoval in Hibernate.