Java-Jpa-Hibernate Detached entity pases to persist on merge

Question

I´m trying to merge an Entity that have a @OneToMany relationship using JPA but it throws the detached entity pased to persist error. I´m not persisting the entity, i´m merging it. I only have the problem while loading the Alumno entity with his Matricula entities using join fetch. Here is the code:

Note: Alumno means Student, Asignatura means Subject and Matricula means Student-Subject, is the relationship between one Student and his Subjects. The relationship is ManyToMany with extra table.

More detailed: Get the Student with the next query: "select a from Student a inner join fetch a.matriculas where iduser=:iduser and password=:password". Then I close the entity manager and change the name of the student. When I try to merge (using entityManager.merge(student)) the student I get the detached entity pased to persist error. If the List on the entity Alumno is null I don´t have the problem.

First entity:

package com.sdi.model;

import java.util.ArrayList;
import java.util.List;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
@Table(name = "Alumno")
public class Alumno implements UsuarioRegistrado {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Long id;
    private String nombre, apellidos, iduser, email, password;
    private boolean cuentaActivada;

    @OneToMany(mappedBy="alumno")
    private List<Matricula> matriculas = new ArrayList<Matricula>();

    public Alumno() { }

    public Alumno(Long id) {
        setId(id);
    }

    public String getNombre() {
        return nombre;
    }

    public void setNombre(String nombre) {
        this.nombre = nombre;
    }

    public String getApellidos() {
        return apellidos;
    }

    public void setApellidos(String apellidos) {
        this.apellidos = apellidos;
    }

    public String getIduser() {
        return iduser;
    }

    public void setIduser(String iduser) {
        this.iduser = iduser;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public Long getId() {
        return id;
    }

    public boolean isCuentaActivada() {
        return cuentaActivada;
    }

    public void setCuentaActivada(boolean cuentaActivada) {
        this.cuentaActivada = cuentaActivada;
    }

    public List<Matricula> getMatriculas() {
        return matriculas;
    }

    public void setMatriculas(List<Matricula> matriculas) {
        this.matriculas = matriculas;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((id == null) ? 0 : id.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Alumno other = (Alumno) obj;
        if (id == null) {
            if (other.id != null)
                return false;
        } else if (!id.equals(other.id))
            return false;
        return true;
    }

    @Override
    public String toString() {
        return "Alumno [id=" + id + ", nombre=" + nombre + ", apellidos="
                + apellidos + ", iduser=" + iduser + ", email=" + email
                + ", password=" + password + ", cuentaActivada="
                + cuentaActivada + "]";
    }

    @Override
    public String paginaPrincipal() {
        return "/alumno/alumno-opciones.xhtml";
    }

    public void addMatricula(Matricula matricula){
        if(!getMatriculas().contains(matricula)){
            getMatriculas().add(matricula);
            matricula.setAlumno(this);
        }
    }

    @Override
    public List<Docencia> getImparte() {
        return null;
    }

}

Second entity: package com.sdi.model;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.IdClass;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@Table(name="MATRICULADO")
@IdClass(MatriculaPk.class)
public class Matricula {

    @Id @ManyToOne
    private Alumno alumno;
    @Id @ManyToOne
    private Asignatura asignatura;

    public Matricula() { }

    public Matricula(Alumno alumno, Asignatura asignatura) {
        this.alumno = alumno;
        this.asignatura = asignatura;
        alumno.addMatricula(this);
        asignatura.addMatricula(this);
    }

    public Alumno getAlumno() {
        return alumno;
    }

    public void setAlumno(Alumno alumno) {
        this.alumno = alumno;
    }

    public Asignatura getAsignatura() {
        return asignatura;
    }

    public void setAsignatura(Asignatura asignatura) {
        this.asignatura = asignatura;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((alumno == null) ? 0 : alumno.hashCode());
        result = prime * result
                + ((asignatura == null) ? 0 : asignatura.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Matricula other = (Matricula) obj;
        if (alumno == null) {
            if (other.alumno != null)
                return false;
        } else if (!alumno.equals(other.alumno))
            return false;
        if (asignatura == null) {
            if (other.asignatura != null)
                return false;
        } else if (!asignatura.equals(other.asignatura))
            return false;
        return true;
    }

    @Override
    public String toString() {
        return "Matricula [alumno=" + alumno + ", asignatura=" + asignatura
                + "]";
    }

}

And this is the merge operation:

@Override
public Object execute() throws BusinessException {
    return Jpa.getManager().merge(alumno);
}

Answer 1

There is a bug using @IdClass on hibernate and that is what was causing the error. The easiest solution is to avoid using @IdClass and create a @Id for the entity (Matricula) between Subject and Student.

Answer 2

If Student has Subject, you need to Manage it to the current transaction.

You will need to do a code like:

beginTransaction();
entityManager.persist(matricula);
Subject subject = getSubjectUsingEntityManager(subjectId);
newStudent.setMatricula(matricula);
newStudent.addSubject(subject);
commitTransaction();