Question

I have the following entity classes:

public class Usuario implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "Id")
    private Integer id;
    @Size(max = 255)
    @Column(name = "Senha")
    private String senha;
    @Size(max = 255)
    @Column(name = "Nome")
    private String nome;
    @ManyToMany(mappedBy = "usuarioCollection", fetch = FetchType.EAGER)
    private Collection<Grupo> grupoCollection;      

}

and

public class Grupo implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "Id")
    private Integer id;
    @Size(max = 255)
    @Column(name = "Nome")
    private String nome;
    @JoinTable(name = "usuario_grupo", joinColumns = {
        @JoinColumn(name = "GrupoID", referencedColumnName = "Id")}, inverseJoinColumns = {
        @JoinColumn(name = "UsuarioID", referencedColumnName = "Id")})
    @ManyToMany(fetch = FetchType.EAGER)
    private Collection<Usuario> usuarioCollection;

}

These codes were generated by netbeans.

When I try to persist it with JPA

entityManager.persist(usuario);

It executes, but there is no registers in the usuario_grupo table.

ie, the usuario is registered in the table (the grupo already exists in the table grupo), but the usuario_grupo doesn’t.

Do you know how I can do this properly?

NOTE: some names are in portuguese.

Answer 1

JPA does not like Collection. It works with Set (unordered collections), List (ordered collections), I believe also with HashMap (I have not needed that so I am not sure).

If your bean must have the Collection attribute, make it transient and make a new attibute (the get and set methods, at least) that manages that Collection as a Set or List.