Spring Data JPA-使用现有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，有一个使用SchoolDTO的创建方法(目前它的结构与实体相同(。

当我发布DTO时，嵌套的子列表级别仅使用现有的级别ID填充(因为级别是以前创建的(。

当我尝试通过JPARepository保存方法进行保存时。。。引发此消息的异常：

"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:

通过迭代每个级别Id来解决问题。。。使用JPA Repository方法getOne(调用entityManager.getReference(获取引用然后加载正确的模型，然后成功地持久化。

@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"正确方式吗？或者，还有更好的方法吗？

Answer 1

在addLevelToPackage函数中，如果我认为schoolService将只返回具有给定id的实体School的一个实例，为什么使用mapschoolService.findById(id).map..。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));
...