[FIXED] Retrieving a field on a relation based on the FK

Issue

I am taking my first steps into jpa (porting the whole db from jdbc to jpa) and i was wondering how i can achieve the following: I have two tables, a Users table and a ProfileImages table, the ProfileImages table consists in a FK to user_id and then another field which is a byte array (which holds the image's bytes).

What i am trying to achieve is being able to recover the byte array directly in my User model, something in the lines of:

@Entity
@Table(name = "users")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "users_userid_seq")
    @SequenceGenerator(name = "users_userid_seq", sequenceName = "users_userid_seq", allocationSize = 1)
    private Long userId;

    @Column
    private String name;

    @Column
    private String surname;

    @Column(nullable = false, unique = true)
    private String username;

    @Column(nullable = false, unique = true)
    private String email;

    @Column
    private String password;

    @Column(nullable = false, unique = true)
    private Integer fileNumber;

    @Column
    private boolean isAdmin;

    // Map the byte array from the profile_image relation
    private byte[] image;

    .....
    .....
}

Note: It'd be optimal to not change the schema to make the user hold the byte array.

Solution

You can use the SecondaryTable annotation to map two tables to one Entity:

@Entity
@Table(name = "users")
@SecondaryTable(name = "profileimages",
                pkJoinColumns = @PrimaryKeyJoinColumn(name = "user_id"))
public class User {

    @Column(name = "image", table = "profileimages")
    private byte[] image;

Please also check out the documentation: https://docs.jboss.org/hibernate/orm/5.5/userguide/html_single/Hibernate_User_Guide.html#sql-custom-crud-secondary-table-example

Answered By - Simon Martinelli