CODEWITHSUNDEEP
javahibernate
Giovani Vercauteren
Giovani Vercauteren

Reputation: 1908

Java - Hibernate one class can reference one of multiple classes

I have one class that can reference one of multiple of classes.

The old classes are as structured as follows:

public class CarOne {
    private int id; 
    private int type; //one
    ...
}

public class CarTwo {
    private int id;
    private int type; //two
    ...
}

public class CarThree {
    private int id;
    private int type; //three
    ...
}

They are NOT SupperMapped and they all exist in their own table with their own ID. There's nothing I can change about this, as it's been in production like this for quite a while now.

Now I need to add a new class:

public class Numberplate {
    //here I'd like a one to one mapping to one of the classes?
}

One option I can think of myself is that I could add the OneToOne relation on the car objects, but I was hoping there was an option to use the 'id' and the 'type' as a discriminator to put the relation on the Numberplate side. Is there such a possibility?

(disclaimer: the examples are purely fictional, but the situation is not.)

Upvotes: 1

Views: 179

Answers (2)

Abass A
Abass A

Reputation: 743

Why dont you use a TABLE_PER_CLASS Strategy ? with this strategy only concrete class have a corresponding table in database and the super class is only for sharing and grouping purpose.

Exemple you define an abstract class for all your CarClass (CarOne, CarTwo...) with a compounded primary key which is id and type.

@Embeddable
public class CarKey implements Serializable{
public Long id;
public String type;
}

Here you abstract class parent of all your car class

@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class SuperCar{
@EmbeddedId
public CarKey id;

 // Getter & Setter
}

Here code for each subclass

@Entity
public class CarOne extends SuperCar{

// specific attribute
}

Here code for your Nameplate class

@Entity
public class Numberplate {

@OneToOne
@JoinColumns({
 @JoinColumn(name="car_id",referencedColumnName = "id"),
 @JoinColumn(name="car_type",referencedColumnName = "type")
})
public SuperCar car;
}

Just take care of performance issue with this strategy especially if you have many subclasses.

Upvotes: 1

Federico Paparoni
Federico Paparoni

Reputation: 722

You can use the joined inheritance type, creating a superclass Car and then CarOne,CarTwo,CarThree must extend it. You can find a complete example of joined here

Upvotes: 1

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