Question

鉴于我有3个带有@OneToMany双向映射的JPA实体，而MyEntity是根级实体：

@Entity
public class MyEntity extends AbstractEntity<Long> {

    @OneToMany(mappedBy = "myEntity", cascade = ALL, orphanRemoval = true)
    private List<OtherEntity> otherEntities = new LinkedList<>();

}

@Entity
public class OtherEntity extends AbstractEntity<Long> {

    @ManyToOne
    private MyEntity myEntity;

    @OneToMany(mappedBy = "otherEntity", cascade = ALL, orphanRemoval = true)
    private List<YetAnotherEntity> yetAnotherEntities = new LinkedList<>();

}

@Entity
public class YetAnotherEntity extends AbstractEntity<Long> {

    @ManyToOne
    private OtherEntity otherEntity;

}

我想创建MyEntity的副本，根据过滤条件删除少数OtherEntity，然后使用Jackson将其序列化为OutputStream（导出）

我怎样才能实现它？

我试图使用：

@PersistenceContext
private EntityManager em;

并致电：em.detach(myEntity);，但这会产生org.hibernate.AssertionFailure: possible non-threadsafe access to session

编辑：添加导出服务方法：

@Override
public void export(MyEntity myEntity, OutputStream out) throws IOException {

    em.detach(myEntity);

    MyEntity myEntityToBeExported = new MyEntity();
    // filter out OtherEntities which we don't want to export
    List<OtherEntity> filteredOtherEntities = myEntity.getOtherEntities().stream()
            .filter(otherEntity -> ...)
            .collect(Collectors.toList());
    myEntityToBeExported.addOtherEntities(filteredOtherEntities);

    ObjectMapper mapper = mapperProvider.mapper();
    mapper.writeValue(out, myEntityToBeExported);
}

使用@OneToMany JPA映射克隆管理实体

0 个答案: