Spring Boot，JPA/Hibernate DTO，ManyToOne

Question

这是我第一个使用Spring/Spring Boot的项目。这是一个使用User和Bookmark实体的简单书签服务。对于每个控制器，创建/发布DTO时会创建并验证。如果DTO有效，我实例化一个新的用户或书签。

我遇到的问题是，当我创建一个新书签时，书签表中的user_id列为空。我将发布以两个域对象，DTO和控制器开始的代码。

用户

@Entity 
public class User { 

@Id 
@GeneratedValue(strategy = GenerationType.IDENTITY) 
private Long id; 

@Column(unique = true, nullable = false) 
private String username; 
private String password; 

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

@Column(name = "role", nullable = false) 
@Enumerated(EnumType.STRING) 
private Role role; 

@OneToMany(mappedBy = "user") 
private List<Bookmark> bookmarks; 

public User() { } 

public Long getId() { 
    return id; 
} 

//getters and setters and toString. 
} 

书签

@Entity 
public class Bookmark { 

@Id 
@GeneratedValue(strategy = GenerationType.AUTO) 
private Long id; 

private String url; 

@Column(length = 2048) 
private String description; 

@ManyToOne() 
private User user; 

public Bookmark() { } 

//getters and setters and toString. 
} 

用户DTO

public class UserCreateForm { 

@NotEmpty 
private String username = ""; 

@NotEmpty 
private String password = ""; 

@NotEmpty 
private String passwordConfirmation = ""; 

@NotEmpty 
@Email 
private String email = ""; 

@NotNull 
private Role role = Role.USER; 

//getters and setters and toString. 
} 

书签DTO

public class BookmarkCreateForm { 

@NotEmpty 
@URL 
private String url=""; 

private String description=""; 

private Long userId; 

public BookmarkCreateForm() { } 

//getters and setters and toString. 
} 

真的只有书签控制器在这里很重要，所以我会跳过UserController，但可以根据需要添加它。

BookmarkController

@RestController 
public class BookmarkController { 

private final UserService userService; 

private final BookmarkSerivce bookmarkSerivce; 

@Autowired 
public BookmarkController(UserService userService, BookmarkSerivce bookmarkSerivce) { 
    this.userService = userService; 
    this.bookmarkSerivce = bookmarkSerivce; 
} 

@RequestMapping("{userId}/add") 
public Bookmark addBookmark(@PathVariable("userId") Long userId, @RequestBody BookmarkCreateForm form) { 

    User user = userService.getUserById(userId) 
      .orElseThrow(() -> new NoSuchElementException(String.format("User=%s not found", userId))); 

    System.out.println(form.getUserId()); 
    Bookmark bookmark = bookmarkSerivce.create(form); 

    return bookmark; 
} 

}

而且BookmarkServiceImpl

@Service 
public class BookmarkServiceImpl implements BookmarkSerivce { 

private final BookmarkRepository bookmarkRepository; 

@Autowired 
public BookmarkServiceImpl(BookmarkRepository bookmarkRepository) { 
    this.bookmarkRepository = bookmarkRepository; 
} 

@Override 
public Bookmark create(BookmarkCreateForm form) { 
    Bookmark bookmark = new Bookmark(); 
    bookmark.setUrl(form.getUrl()); 
    bookmark.setDescription(form.getDescription()); 

    return bookmarkRepository.save(bookmark); 
} 
} 

Answer 1

我是一个傻瓜。解决方案很简单，我在dunni问我发布BookmarkService后意识到了这一点。

BookmarkCreateForm（DTO）没有User属性。所以在BookmarkService中，当设置书签对象的属性时，用户永远不会被设置。显然，JPA/Hibernate无法映射不存在的用户。

代码：

public class BookmarkCreateForm { 

@NotEmpty 
@URL 
private String url=""; 

private String description=""; 

private User user; 

public BookmarkCreateForm() { } 

//getters/setters 
} 

BookmarkService

@Service 
public class BookmarkServiceImpl implements BookmarkSerivce { 

private final BookmarkRepository bookmarkRepository; 

@Autowired 
public BookmarkServiceImpl(BookmarkRepository bookmarkRepository) { 
    this.bookmarkRepository = bookmarkRepository; 
} 

@Override 
public Bookmark create(BookmarkCreateForm form) { 
    Bookmark bookmark = new Bookmark(); 
    bookmark.setUrl(form.getUrl()); 
    bookmark.setDescription(form.getDescription()); 
    bookmark.setUser(form.getUser()); 

    return bookmarkRepository.save(bookmark); 
} 

}

BookmarkController

@RestController 
public class BookmarkController { 

private final UserService userService; 

private final BookmarkSerivce bookmarkSerivce; 

@Autowired 
public BookmarkController(UserService userService, BookmarkSerivce bookmarkSerivce) { 
    this.userService = userService; 
    this.bookmarkSerivce = bookmarkSerivce; 
} 

@RequestMapping("{userId}/add") 
public Bookmark addBookmark(@PathVariable("userId") Long userId, @RequestBody BookmarkCreateForm form) { 

    User user = userService.getUserById(userId) 
      .orElseThrow(() -> new NoSuchElementException(String.format("User=%s not found", userId))); 

    form.setUser(user); 
    Bookmark bookmark = bookmarkSerivce.create(form); 

    return bookmark; 
} 

}