Question

有关联实体的简单模型：

MainModel类

@Entity 
@Table(name = "main_model")
public class MainModel 
{
    @Id 
    @GeneratedValue(strategy = GenerationType.IDENTITY) 
    private long id;

    @OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinColumn(name = "id_main_model", referencedColumnName = "id")
    private List<AssociatedModel> am_collection;

    public MainModel() { }

    public long getId()
    {
        return this.id;
    }

    public void addAssociated(AssociatedModel am)
    {
        am_collection.add(am);
    }
}

AssociatedModel类

@Entity 
@Table(name = "associated_model")
public class AssociatedModel
{
    @Id 
    @GeneratedValue(strategy = GenerationType.IDENTITY) 
    private long id;

    public AssociatedModel() { }

    public long getId()
    {
        return this.id;
    }
}

MainModel的最简单的jpa存储库

public interface MainModelDAO extends JpaRepository<MainModel, Long>  
{
}

最后，控制器创建和保存AssociatedModel实例的方法

@RequestMapping("/url")
public String createAssociated(@RequestParam("id_mainmodel") long id_mainmodel, @RequestBody AssociatedModel newAm) 
{
    MainModel mm = MainModelDAOobject.findOne(id_mainmodel);// MainModelDAOobject - @Autowired
    mm.addAssociated(newAm);
    MainModelDAOobject.saveAndFlush(mm);
    return String.valueOf(newAm.getId());// get Id of associated saved object
}

关联对象正确保存到数据库中，但getId()方法允许此对象的 id 值始终零。如何正确获取保存的关联对象的ID？

Answer 1

保存值后尝试调用MainModelDAOobject.flush()，但在读取ID之前。

请参阅this answer以获取解释。

修改：尝试通过添加新行手动保存newAm：

mm.addAssociated(newAm); // Existing line
newAm = MainModelDAOobject.save(newAm); // New line
MainModelDAOobject.save(mm); // Existing line

Answer 2

你需要一个序列生成器：

@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "MainModel SequenceGenerator")
@SequenceGenerator(name = "MainModel SequenceGenerator", sequenceName = "MainModel Sequence", initialValue = SEQUENCE_INITIAL_VALUE, allocationSize = SEQUENCE_ALLOCATION_SIZE)

Answer 3

感谢 David Levesque 提供有用的建议。

问题解决如下：

需要AssotiatedModel的其他存储库

public interface AssotiatedModelDAO扩展了JpaRepository {}
然后手动保存关联对象：

mm.addAssociated（newAm）;

newAm = AssotiatedModelDAOobject.save（newAm）;

newAm = MainModelDAOobject.save（newAm）`;

MainModelDAOobject.save（毫米）;

保存后获取关联对象的ID

3 个答案: