JPA: Foreign key that is also a primary key mapping

Question

I have been trying to solve this for whole day but no luck! Also i tried to read most of the tutorials on the net but as you all know they all are full of useless examples t

Answer 1

Why don't you use an @Embedded object? When using an embedded object, you get the logical separation you desire in your code and keep your database compliant with Entity-Relational Normalization rules.

It's weird to think on a One-to-One relationship, because even though JPA/Hibernate allows it, all data should be stored in the same table, making you model simpler, while also simplifying queries and increasing database performance by removing the need for a Join operation.

When using Embedded objects you don't have to worry about mapping IDs and bizarre relations, since your ORM is capable of understanding that your just making a code separation, instead of demanding an actual relation of One-to-One between tables.

class Vehicle {
    @Id
    @Column(name = "ID")
    private long vehicleId; 
    @Column(name = "BRAND")
    private String brand; 
    @Column(name = "MODEL")
    private String model;
    @Column(name = "DEV_YEAR")
    private int devYear;
    @Column(name = "REG_NUMBER")
    private int regNumber;

    @Embedded
    private TravelExtra extras;

    // Constructor, getters and setters...

}

.

@Embeddable
class TravelExtras {

    @Column(name = "ALLOW_SMOKE")
    private boolean allowSmoke; 
    @Column(name = "ALLOW_FOOD")
    private boolean allowFood;
    @Column(name = "ALLOW_DRINKS")
    private boolean allowDrinks;
    @Column(name = "AIR_CONDITIONER")
    private boolean airConditioner;

    // Default Constructor, getters and setters...
}