JPA ElementCollection Map<Integer, Entity>

Question

i need to assign the value of the map to my entity but jpa tries to save the hole object as an byte array.

@Entity
public class ImageSet {
    ...
    @ElementCollection
    private Map<Integer, Image> images = new LinkedHashMap<>();
}

@Entity
public class Image {
    ...
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
}

I think it is not that hard but i cant find any examples online. Could you please help me? thank you very much!

Answer 1

Association annotated with @ElementCollection is valid for the following mapping types:

• Map<Basic,Basic>
• Map<Basic,Embeddable>
• Map<Embeddable,Basic>
• Map<Embeddable,Embeddable>
• Map<Entity,Basic>
• Map<Entity,Embeddable>

Association annotated with @OneToMany / @ManyToMany is valid for the following mapping types:

• Map<Basic,Entity> (this is your case)
• Map<Embeddable,Entity>
• Map<Entity,Entity>

---

According to the above rules the entities may look as follows:

@Entity
public class ImageSet {
    ...
    @OneToMany(mappedBy="container")
    @MapKey //map key is the primary key
    private Map<Integer, Image> images = new LinkedHashMap<>();
}

@Entity
public class Image {
    ...
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @ManyToOne
    private ImageSet container;
}

Note that bidirectional association between ImageSet.images and Image.container is optional, but removing it would create an additional table in the database.