Spring Data JPA - 使用現有嵌套子項持久化新對象

Question

我確實有兩個名為 School 和 Level 的實體，它們具有多對多關系。

@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，有一個采用 SchoolDTO 的 create 方法（現在它與實體具有相同的結構）。

當我發布 DTO 時，嵌套的子列表 Levels 僅填充了現有的 Levels id（因為之前創建了 Levels）。

當我嘗試通過 JPARepository 保存方法保存時...拋出此消息的異常：

"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:

問題是通過迭代每個 Level Id 來解決的……使用 JPA Repository 方法getOne （調用entityManager.getReference ）獲取引用，然后加載正確的模型，然后成功持久化。

@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());
    }

我的問題是：這是在 Spring Data 中發布關聯的“唯一”正確方法嗎？ 或者，有沒有更好的辦法？

Answer 1

在addLevelToPackage函數中為什么使用map schoolService.findById(id).map..如果我認為 schoolService 將僅返回具有給定 id 的實體 School 的一個實例。 我認為用以下內容替換地圖就足夠了：

...
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));
...