CODEWITHSUNDEEP
javahibernatejpaormmapping
MDP
MDP

Reputation: 4267

Entity mapped by other many different Entities (with Hibernate)

I know my title is not clear, but I don't know how to explain my question with few words.

I have two classes with a bidirectional mapping. Image.class:

@Entity
@Table(name = "image")
public class Image{

    @Id
    @Column(name = "id")
    @GeneratedValue
    Long id;

    @OneToOne(targetEntity = Father.class)
    @JoinColumn(referencedColumnName = "id", name="father")
    @Size(min = 1, max = 11)
    Father father;

}

and Father.class:

class Father{

      @Id
      @Column(name = "id")
      @GeneratedValue
      Long id;

      @OneToOne(mappedBy = "father")  
      Image pic;
}

Now, I'd like to use Image.class as field of other classes. Let's say I have Mother.class

 class Mother{

          @Id
          @Column(name = "id")
          @GeneratedValue
          Long id;

          @OneToOne(mappedBy = "mother")  
          Image pic;
    }

My question is: how should I edit the "mapping" of Image.class?

Of course Image.class cannot have a field like Father father, since in the last scenario Image.class is a field of Mother.class and is not a field of Father.class.

I remember that there was I way that allow you to save, in a single table, an Entity that can be mapped by many different Entities. I remember that I needed to add a field in the table that distinguishes wheter Image.class is "bound" to Father.class or Mother.class.

I'm no more able to find that documentation on the internet.

Upvotes: 3

Views: 513

Answers (1)

Thomas
Thomas

Reputation: 88707

Note that "field" is not the right term to describe a relation. Father and Mother would have a relation to Image and this could be unidirectional, i.e. Image wouldn't know which entity it belongs to.

This probably is the most sensible way to go and if there are no good reasons to require a bidirectional relation I'd suggest you go the unidirectional route. To make the relation unidirectional you'd have to make Mother and Father the owning side, i.e. put the image id into their tables and remove the mappedby from their @OneToOne while removing the mapping from Image entirely.


If you really need to know that and need Hibernate to be able to navigate the relation then you'd have to use a common super class (also needs to be an entity even if there are no instances) and probably table-per-class inheritance.

Besides that you could store information about who is related to the image in Image itself and do the lookup manually.

Upvotes: 4

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