How to cascade @ManyToOne bidirectional relations with cascading?

Question

I want to automatically persist/merge Address entities of persons. Once created, they should be updateable by any person, but not removed if a Person is removed.

//each person can only have one address
@Entity
public class Person {
    @ManyToOne
    private Address address;
}


//one address can be assigned to multiple persons (eg family members)
@Entity
public class Address {
    @OneToMany
    private List<Person> persons;
}

Questions:

1. How would I have to write the cascade annotations for this requirement?
2. How would I create those entities? person.setAddress(address) or address.getPersons().add(person)?

Answer 1

I think the @Cascade({CascadeType.MERGE}) on both would be what you are looking for.

I would probably create and persist a Person without an address, and then in the Address entity have something like:

public void addPerson(Person person) {
   persons.add(person);
   person.setAdderess(this);
}

Hope this helps.

Answer 2

1. To answer your first question, for your desired requirement you should use cascade=CascadeType.REMOVE to avoid removing an Address if a Person is removed:

@OneToMany(cascade = CascadeType.REMOVE mappedBy = "person")

You may take a look at this article it explains the same behavior in the same situation, saying that:

If only cascade=CascadeType.REMOVE is specified no automatic action is taken since removing a relationship is not a remove operation.

2. For the second question to persist both entities you should use the two statements together, like this:

person.setAddress(address);
address.getPersons().add(person);

Take a look here for further information.