CREATE TABLE `categories` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `parent_id` bigint(20) unsigned NOT NULL DEFAULT '0' COMMENT '父分類ID',
  `code` varchar(255) NOT NULL DEFAULT '' COMMENT '分類代碼',
  `title` varchar(255) NOT NULL DEFAULT '' COMMENT '分類名稱',
  `status` tinyint(1) NOT NULL DEFAULT '0' COMMENT '狀態(tài)1啟用0禁用',
  `created_at` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP,
  `updated_at` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB;

@Entity
@DynamicUpdate
@Table(name = "categories")
public class Category {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private BigInteger id;
    // 為了設置關聯(lián)關系，需要注釋掉.
    // 反正這里沒搞明白，沒設關聯(lián)關系前，設了Column()返回的數(shù)據(jù)中字段不對了。
    // 這里后面再研究吧
    // private BigInteger parent_id;
    @CreationTimestamp
    @Column(nullable = false, updatable = false)
    private Date created_at;
    @UpdateTimestamp
    @Column(nullable = false)
    private Date updated_at;
    private String title;
    private String code;
    private int status;
    // 中間省略  set get 代碼
    // 關聯(lián)關系
    @ManyToOne
    // 查不到記錄就忽略
    @NotFound(action= NotFoundAction.IGNORE)
    // 外鍵是parent_id
    @JoinColumn(name = "parent_id")
    private Category parent;
    public Category getParent() {
        return parent;
    }
    public void setParent(Category p) {
        this.parent = p;
    }
}

public interface CategoryRepository extends JpaRepository<Category, BigInteger>, JpaSpecificationExecutor<Category> {
    List<Category> findAllByCode(String code);
    @Query(value = "select * from categories WHERE parent_id=?1 ", nativeQuery = true)
    List<Category> findAllByParentId(BigInteger pid);
    @Transactional
    @Modifying
    @Query(value="update Category c set c.status=?2 where c.id in ?1")
    void updateStatusById(List<BigInteger> ids, Integer status);
}

@RestController
@RequestMapping(value = "/api/category")
public class CategoryController {
    private CategoryRepository categoryRepository;
    public CategoryController(CategoryRepository categoryRepository) {
        this.categoryRepository = categoryRepository;
    }
    @GetMapping(value = "fetch-child")
    public List<Category> getChildren(@RequestParam(value = "id", required = true, defaultValue = "0") BigInteger id) {
        return categoryRepository.findAllByParentId(id);
    }
    /**
     * 修改記錄
     * @param category
     * @return
     */
    @PostMapping(value = "")
    public @ResponseBody String store(@RequestBody StoreCategoryData category) {
        System.out.println(category.toString());
        Optional<Category> row = categoryRepository.findById(category.parentId);
        if (row.isPresent()) {
            Category p = row.get();
            Category c = new Category();
            c.setParent(p);
            c.setTitle(category.title);
            c.setCode(category.code);
            categoryRepository.save(c);
            return "saved";
        }
        throw new RuntimeException("父分類不存在");
    }
}

public class StoreCategoryData {
    public String title;
    public String code;
    public BigInteger parentId;
}