Question

I am trying to create relationships between different persons but couldn’t find a way on how to do it using JPA. Below is the model given to support the requirement:

Person table:
Id FirstName LastName
1 John          Heller
2 Joseph      Heller
3 Andrew      Heller
4 Steven      Heller

Person_Relationship table
Id Person1 Person2 Relationship
1 1             2             Parent
2 2             1             Child
3 1             3             Sibling
4 3             1             Sibling
5 4             1             Secretary

Can someone please share your experience if you have ever implemented the above using Hibernate as JPA provider.

Answer 1

The easiest way is to use a OneToMany association between a Person entity and a RelationShip entity, each entity mapping the associated table:

public class Person {
    @OneToMany(mappedBy = "person1")
    private List<RelationShip> relationships;

    public List<Person> getSiblings() {
        List<Person> result = new ArrayList<Person>();
        for (RelationShip r : relationShips) {
            if (r.getType() == RelationshipType.SIBLING) {
                result.add(r.getPerson2());
            }
        }
    }

    ...
}