Mapped OneToOne returning null in relationship owner

Hibernate ORM
1

Hi all, I’m having a problem with a one-to-one mapping between a Contract class and a Vehicle, where trying to access the Vehicle associated with the Contract gives a null pointer exception.
When I try to access vehicleSold, it says:

Cannot invoke "com.example.vehicle_workshop.models.Vehicle.getPrice()" because the return value of "com.example.vehicle_workshop.models.SalesContract.getVehicleSold()" is null

Here are the following classes:

@Data
@MappedSuperclass
public abstract class Contract {
    private String date;
    private String customerName;
    private String customerEmail;
    @OneToOne
    @PrimaryKeyJoinColumn(name = "vin")
    private Vehicle vehicleSold;
}

Here’s an implementation:

@EqualsAndHashCode(callSuper = false)
@Data
@AllArgsConstructor
@NoArgsConstructor
@Entity
public class SalesContract extends Contract {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long salesContractId;
    private boolean financed;
   // irrelevant methods not shown
}

Here’s the Vehicle:

@Data
@AllArgsConstructor
@NoArgsConstructor
@Entity
public class Vehicle {
    @Id
    private String vin;
    private int year;
    private String make;
    private String model;
    private String vehicleType;
    private String color;
    private int odometer;
    private double price;
}

I’ve checked that there’s valid entries to use, and that there’s a VIN in the SalesContract table that matches up to the Vehicle table

2

Please remove @PrimaryKeyJoinColumn, as that does not have the effect you’re trying to achieve and instead makes the association owned by the Vehicle entity type: you should use @JoinColumn instead to specify which column the foreign key points to, but since vin is the primary key of the target entity you can also not specify anything since that’s the default.