Is this a ManyToMany JPA/Hibernate relationship or there is another way to map this ?

Question

Hi,

I'm getting started with JPA and created the following (simplified) tables;

airport
--------
id (pk)
city
code
...

trip
--------
id (pk)
originAirport_id  (fk)
destinationAirport_id  (fk)
...

I'm trying to map this in JPA/Hibernate.

In My trip object I created 2 airport objects:

private Airport airportFrom;
private Airport airportTo;

And I annotated the getters like this:

    @ManyToOne
public Airport getAirportFrom() {
 return airportFrom;
}

    @ManyToOne
public Airport getAirportTo() {
 return airportTo;
}

In my Airport class I created a HashSet of 'trip' objects

    private Set <Trip> trips = new HashSet<Trip>();

And annotated the getter:

    @OneToMany (mappedBy="airport")
public Set <Trip> getTrips() {
 return trips;
}

This would be simple to implement in SQL but I don't know how to annotate and implement that relationship in JPA/Hibernate.

Any tips?

Answer 1

I believe you missed a little detail. In the Airport class, the Set<Trip> trips you have must correspond to what is in the other table. I would suggest:

    public class Airport {
       private Set<Trip> fromTrips = new HashSet<Trip>();
       private Set<Trip> toTrips = new HashSet<Trip>();

       @OneToMany (mappedBy="airportFrom")
       public Set <Trip> getFromTrips() {
          return fromTrips;
       }
       @OneToMany (mappedBy="airportTo")
       public Set <Trip> getToTrips() {
          return fromTrips;
       }

    }

The "mappedBy" must point toward the name of a property in the Many class. Here, the two properties in Trip are airportFrom and airportTo.

So you have two Sets of Trips, the fromTrips and the toTrips. I hope you are ok with this?

---

Edited, after an excellent comment by ChssPly76, that would deserve to be an answer of its own. I would vote for it :-)

If the association needs to be bi-directional that's the way to map it. I'm not sure it has to be, though - Airport has no business dealing with collections of trips. Consider making the association uni-directional instead and using a query when / if you need to find all the trips taken from / to airport in question (you'll be able to get a single list this way too).