Spring Data JPA - 使用现有的嵌套子对象持久化新对象

Question

我确实有两个实体，称为 School 和 Level，具有多对多关系。

@Data
@Entity
public class School {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "school_generator")
    @SequenceGenerator(name="school_generator", sequenceName = "school_seq", allocationSize=1)
    @Column(name = "school_id")
    private Long id;

    @NotBlank
    private String name;

    @NotBlank
    private String city;

    @ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
    @JoinTable(
            name = "school_level",
            joinColumns = @JoinColumn(name = "school_id"),
            inverseJoinColumns = @JoinColumn(name = "level_id"))
    private Set<Level> levels = new HashSet<>();

}

@Data
@Entity
public class Level implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "level_generator")
    @SequenceGenerator(name = "level_generator", sequenceName = "level_seq", allocationSize = 1)
    @Column(name = "level_id")
    private Long id;

    @NotBlank
    @Column(nullable = false, unique = true)
    private String name;

}

我的SchoolController，Rest 控制器，有一个 create 方法，它接受一个 SchoolDTO（现在它与实体具有相同的结构）。

当我发布 DTO 时，嵌套的子列表关卡仅填充现有关卡 ID（因为关卡是之前创建的）。

当我尝试通过 JPARepository 保存方法保存时...抛出此消息的异常：

"detached entity passed to persist: com.salimrahmani.adawat.domain.Level; nested exception is org.hibernate.PersistentObjectException: detached entity passed to persist: com.salimrahmani.adawat.domain.Level",
    "trace": "org.springframework.dao.InvalidDataAccessApiUsageException: detached entity passed to persist:

通过遍历每个 Level Id 来解决问题...使用 JPA 存储库方法 getOne（调用 entityManager.getReference）获取引用 然后加载正确的模型，然后持久化成功。

@PostMapping("/{id}/grades")
public ResponseEntity<SchoolDTO> addLevelToPackage(@PathVariable Long id, @RequestBody @Valid LevelDTO levelDTO) {
        return schoolService.findById(id)
                .map(school -> {
                    Level level = levelMapper.map(levelDTO);

                    if(level.getId() != null) {
                        level = levelService.getOne(level.getId());
                        school.getLevels().add(level);
                    } // else error

                    School saved = schoolService.save(school);

                    return ResponseEntity.ok(schoolMapper.map(saved));

                }).orElseGet(() -> ResponseEntity.notFound().build());
    }

我的问题是：这是在 Spring Data 中发布关联的“唯一”正确方法吗？或者，有没有更好的办法？

Answer 1

在addLevelToPackage 函数中 为什么使用map schoolService.findById(id).map.. 如果我认为schoolService 将只返回具有给定ID 的实体School 的一个实例。 我认为用以下内容替换地图就足够了：

...
School theSchool = schoolService.findById(id);
Level theLevel = levelService.getOne(levelDTO.getId());
theSchool.getLevels().add(theLevel);
School saved = schoolService.save(theSchool);
return ResponseEntity.ok(schoolMapper.map(saved));
...