How to merge a @OneToMany relationship effectively?

For example I have the following two entity classes with a one-to-many relationship:

public class A implements Serializable {
    ...
    @OneToMany(mappedBy = "a", cascade = CascadeType.ALL)
    private List<B> bs;
    ...
}

public class B implements Serializable {
    ...
    @ManyToOne
    private A a;
    ...
}

Suppose I have an instance of A called a, and a.bs == [b1, b2, b3]. Now I want to remove b1 from, and add b4 to the relationship, so that a.bs == [b2, b3, b4], and b1.a == null.

I've tried em.merge(a) after doing a.setBs(b2, b3, b4), but that will result in a.bs == [b1, b2, b3, b4], unless I do an explicit b1.setA(null). However, this can lead to complexity if a.bs changes a lot, and i开发者_开发百科f A has more one-to-many relationships to other entity classes. Setting orphanRemoval = true is also not the solution, because I simply want to set b1.a = null instead of removing b1.

This problem has been perplexing me for quit a long time, anybody that helps me out is greatly appreciated!

you can set cascade style to update on bs and say a.bs.remove(b1); session.update(a);

this would do the trick.

you are telling the ORM to cascade updates on the collection, when you remove an entry from the collection, the corresponding value will be nullified.