Hibernate说列'idRol'不能为空

Question

我正在尝试保存一个有参考usuari和对rol的引用的usuarirol。我检查了Usuari对象和ROL对象是否具有其ID，但是Hibernate告诉我IDROL不能为null。

映射有问题吗？

表T_usuarirol

@Entity
@Table(name = "t_usuariRol"
        , uniqueConstraints = @UniqueConstraint(columnNames = {"idUsuari", "idRol"}))
public class UsuariRol implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
@ManyToOne
@JoinColumn(name = "idUsuari")
private Usuari usuari;
@ManyToOne
@JoinColumn(name = "idRol")
private Rol rol;

表A_rol

@Entity
@Table(name = "a_rol")
public class Rol implements Serializable {
private static final long serialVersionUID = -1979744578967968079L;
static final String PREFIX = "pia.entity.Rol.";
public static final String findAll = PREFIX + "findAll";
public static final String findById = PREFIX + "findById";
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
@Column(length = 45)
private String nom;

usuaribean.saveusuarirol

public void saveUsuariRol(){
 UsuariRol urol;
 Usuari usuari = usuariMgr.findById(1);
 Rol rol = rolMgr.findById(2);  //rol is not null has id and nom
 urol = new UsuariRol(usuari, rol);
 try {
     usuariRolMgr.save(urol);
 } catch (Exception e) {
     System.out.println("error usuarirol with id");
 }

}

错误

Hibernate: 
/* insert UsuariRol / 
insert 
 into
 t_usuariRol
 (idRol, idUsuari, version) 
 values
 (?, ?, ?)
10:25:39,184 WARN  [org.hibernate.engine.jdbc.spi.SqlExceptionHelper] (default task-52) SQL Error: 1048, SQLState: 23000
10:25:39,186 ERROR [org.hibernate.engine.jdbc.spi.SqlExceptionHelper] (default task-52) Column 'idRol' cannot be null
...
Caused by: javax.persistence.PersistenceException: org.hibernate.exception.ConstraintViolationException: could not execute statement
...
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Column 'idRol' cannot be null

Rolmanager

@Stateless
public class RolManager {
    protected Logger logger = Logger.getLogger(getClass().getName());
    @PersistenceContext(unitName = "dbPU")
    protected EntityManager em;
    public Rol findById(int id) {
        return this.em.find(Rol.class, id);
    }
    public List<Rol> all() {
        return this.em.createNamedQuery(Rol.findAll, Rol.class).
                getResultList();
    }
    public Rol save(Rol rol) {
        if (rol.getId() == null) {
            this.em.persist(rol);
            return rol;
        } else {
            return this.em.merge(rol);
        }
    }
    public void delete(int id) {
        try {
            Rol reference = this.em.getReference(Rol.class, id);
            this.em.remove(reference);
        } catch (EntityNotFoundException e) {
            //we want to remove it
            logger.error("Entity not found exeption: ", e);
        }
    }
}

Answer 1

我可以推断出的问题是Hibernate的会话无法跟踪您的子对象。从一个会话中加载并保存在另一个会话中的实体可能会引起问题。

因此，为了解决此问题。

1. 开始会话和交易
2. 获取子对象
3. 保存父对象
4. 然后提交

在上述所有过程中使用相同的会话。