How to create a relationship using JPA that contains attributes?

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How to create a relationship using JPA that contains attributes?

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Hello, I'm working on a Java Web project with Hibernate, Postgres, Glassfish, and use JPA / JSF. The problem is that my relationships were being generated with the following strategy:

 @JoinTable(name = "prop_user", joinColumns = {@JoinColumn(name = "id_prop", referencedColumnName = "idproposicao")}, 
        inverseJoinColumns = {@JoinColumn(name = "id_user", referencedColumnName = "cpf")})
@PrimaryKeyJoinColumn
private UsuarioEntity userProp;

Using the above code in the User entity, I created a relationship with the Proposition entity, generating a relationship table, but I have no control over it. All in done via hibernate by annotation.

And now I need to create an extra field in this relationship, a String "Opinion" attribute and I do not know how to do it with JPA.

I see that it seems that I need to redo the relationships, as I will need to create an entity class for this relationship, manually shaping to my need. Can anyone confirm if I'm on the right track?

Thank you!

jpa

asked by anonymous 07.07.2018 / 23:53

1 answer

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score 0 · Answer 1

Yes, that's the way.

You have a UserEntity class right? One tip, user is already an entity, and you will persist the objects of this class in a database, for the name of your classes get leaner there is no need to put Entity in front of the name of your class, set only as User .

Returning to your question, you want to assign one or several opinions to a given user, in which case you create a new Opinion class and define the objects

@Entity
public class Opiniao implements Serializable {

    private static final long serialVersionUID = 1L;

    private Long id;
    private String opiniao;

    @ManyToOne //para cada opinião você define o usuário responsável pela opinião
    private Usuario usuario;
....

User Class

@Entity
public class Usuario implements Serializable {

    private static final long serialVersionUID = 1L;

    private Long id;
    private String nome;
    ....

In this case the relationship is a user can have several opinions.

This is just a summary, I advise you to do some research on JPA mapping, there are good content on the internet look at this: jpa and good lessons on youtube like this: video