Question

Let’s say we have two tables, ORDERS and OFFERS

Order POJO

@Entity
@Table(name = "ORDERS")
public class Order {

    @Column(columnDefinition = "serial")
    private @Id Integer id;
    private @NotNull @Email String ownerEmail;
    private @NotNull Integer offerId;
}

Offer POJO

@Entity
@Table(name = "OFFERS")
public class Offer {

    @Column(columnDefinition = "serial")
    private @Id Integer id;
    private @Email @NotNull String ownerId;
}

Is it possible to fetch in single query on EntityManager Order by ID so that the result will contain related Offer object?

Like creating @Transient Offer field in Order, because we don’t want to modify Offer data on persisting Order.

Or the only way is to create two queries?

Answer 1

Annotating @Transient on the offer field in Order means that this field will be not mapped and persisted . Indeed , you should map this field but make it as read-only by setting its @Column.insertable() and @Column.updatable() to false.

@Entity
@Table(name = "ORDERS")
public class Order {

    @Column(columnDefinition = "serial")
    private @Id Integer id;
    private @NotNull @Email String ownerEmail;

    private @NotNull Integer offerId;

    @Column(insertable=false , updateable=false)
    private Offer offer;
}

To fetch the order along with its related offer in a single query , you can use the fetch join :

SELECT order FROM Order order join fetch order.offer