JPA - Problems with persist of @ManyToOne

I am working on an application that requires data from faculties and careers to be saved and I have created the following entities:

  

Faculty

@Entity
@Table(name = "uc_facultades", schema = "uc")
@SequenceGenerator(name = "Facultades_id_seq", sequenceName = "uc.uc_facultades_id_seq", allocationSize = 1)
public class Facultad implements Serializable {

    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "Facultades_id_seq")
    @Column(name = "id")
    private Integer id;
    @NotNull
    @Size(max = 70)
    @Column(name = "nombre")
    private String nombre;
    @NotNull
    @Column(name = "estado", columnDefinition = "boolean default true")
    private Boolean estado;
    @OneToMany(mappedBy="facultad", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    private List<Carrera> carreras;

//Getters y Setters

 public void addCarrera(Carrera carrera){
        carreras.add(carrera);
        if(carrera.getFacultad() != this){
            carrera.setFacultad(this);
        }
    }
}

  

Carrera

@Entity
@Table(name="uc_carreras", schema="uc")
@SequenceGenerator(name = "Carreras_id_seq", sequenceName = "uc.uc_carreras_id_seq", allocationSize = 1)
public class Carrera implements Serializable {

    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator="Carreras_id_seq")
    @Column(name="id")
    private Integer id;
    @NotNull
    @Size(max=80)
    @Column(name="nombre")
    private String nombre;
    @NotNull
    @Column(name="estado", columnDefinition="boolean default true")
    private boolean estado = true;
    @ManyToOne(fetch = FetchType.LAZY, optional=false, cascade = CascadeType.ALL, targetEntity = Facultad.class)
    @JoinColumn(name="idfacultad", referencedColumnName="id", nullable = false, insertable = false)
    private Facultad facultad;
    @ManyToMany(cascade = CascadeType.ALL, targetEntity = Pensum.class)
    @JoinTable(name="uc.uc_pensum_carrera", 
            joinColumns=@JoinColumn(name="idcarrera", referencedColumnName="id", nullable = false), 
            inverseJoinColumns=@JoinColumn(name="idpensum", referencedColumnName="id", nullable = false))
    @OrderBy(value = "año DESC")
    private List<Pensum> pensums;

//Getters y Setters
}

This code is with which I register a new career:

@Override
@TransactionAttribute(TransactionAttributeType.REQUIRED) 
public void guardarCarrera(CarrerasDTO carreraDTO) {
        LOG.info("[CarrerasService][guardarCarrera]");
        try {
            Facultad facultad = em.find(Facultad.class, carreraDTO.getFacultad().getId());//Se extrae la entity
            Carrera carrera = new Carrera();
            carrera.setNombre(carreraDTO.getNombre());
            carrera.setFacultad(facultad);    
            carrera.setEstado(Boolean.TRUE);
            carreraDTO.getPensums().stream().forEach(pensum -> {
                carrera.addPensum(pensum); 
            });
            em.persist(carrera);   
            em.flush();
        } catch (Exception e) {
            LOG.log(Level.SEVERE, "[CarrerasService][guardarCarrera] Excepcion -> {0}", e.getMessage());
        }
    }

If I try to persist with CascadeType.PERSIST or CascadeTYpe.ALLme throws the following exception:

Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.7.0.v20170811-d680af5): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: org.postgresql.util.PSQLException: ERROR: llave duplicada viola restricción de unicidad «pk_facultad»

If I use the CascadeType.MERGE it throws me the following exception:

Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.7.0.v20170811-d680af5): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: org.postgresql.util.PSQLException: ERROR: el valor null para la columna «idfacultad» viola la restricción not null

I have been researching and correcting the entities and the method for several days but nothing works. I hope you can help me.

NOTE: For the development of this I am using:

• Java EE 7 (Web Application)
• JPA 2.1 with EclipseLink
• EJB Lite 3.2