错误 - 非空属性引用空值或瞬态值

Question

我是春天的新手。我制作了一个基于两个表之间关系的 API，为此使用 OneToMany 注释和用于 API 测试我有邮递员。我的目标是将请求的数据保存在下面提到的两个单独的实体中。当我尝试在邮递员中发布数据时： 1-3 字段与 Post 实体相关，而 text 字段属于 Comment 实体（cmets 是加入字段）

{
"title": "Post1",
"description": "Post 1 description",
"content": "Post 1 content",
"comments": [
    {
        "text": "Java best selling book"
    },
    {
        "text": "Exploring spring boot"
    }
]

}

我收到如下错误：

Hibernate: insert into posts (content, description, title) values (?, ?, ?)
2021-09-01 11:55:09.786 TRACE 9884 --- [nio-8089-exec-2] o.h.type.descriptor.sql.BasicBinder      
: binding parameter [1] as [VARCHAR] - [Post 1 content]
2021-09-01 11:55:09.786 TRACE 9884 --- [nio-8089-exec-2] o.h.type.descriptor.sql.BasicBinder      
: binding parameter [2] as [VARCHAR] - [Post 1 description]
2021-09-01 11:55:09.786 TRACE 9884 --- [nio-8089-exec-2] o.h.type.descriptor.sql.BasicBinder      
: binding parameter [3] as [VARCHAR] - [Post1]
2021-09-01 11:55:09.815 ERROR 9884 --- [nio-8089-exec-2] o.a.c.c.C.[.[.[/].[dispatcherServlet]    
: Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception 
[Request processing failed; nested exception is 
org.springframework.dao.DataIntegrityViolationException: not-null property references a null 
or transient value : com.techspring.entity.Comment.post; nested exception is 
org.hibernate.PropertyValueException: not-null property references a null or transient value : 
com.techspring.entity.Comment.post] with root cause

我的 MVC 如下：

Post.java

@Entity
@Table(name = "posts")
public class Post {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;
  private String title;
  private String description;
  private String content;
  @OneToMany(cascade = CascadeType.ALL,
        fetch = FetchType.LAZY,
        mappedBy = "post")
  private Set<Comment> comments = new HashSet<>();

  GET, SET;

Comment.java

@Entity
@Table(name = "comments")
public class Comment {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;
  private String text;

  @ManyToOne(fetch = FetchType.LAZY, optional = false)
  @JoinColumn(name = "post_id", nullable = false)
  private Post post;

  Get, Set;

PostController.java

休息控制器 公共类 PostController {

@Autowired
private PostRepository postRepository;

@PostMapping("/posts")
public Post createPost(@Valid @RequestBody Post post) {
    return postRepository.save(post);
}      

CommentController.java

@RestController
public class CommentController {

@Autowired
private CommentRepository commentRepository;

@Autowired
private PostRepository postRepository;


@PostMapping("/posts/{postId}/comments")
public Comment createComment(@PathVariable (value = "postId") Long postId,
                             @Valid @RequestBody Comment comment) {
    return postRepository.findById(postId).map(post -> {
        comment.setPost(post);
        return commentRepository.save(comment);
    }).orElseThrow(() -> new ResourceNotFoundException("PostId " + postId + " not found"));

感谢您的帮助。

Answer 1

您的操作方式Comment comment 是一个新的临时实体，它与已维护的post 实体相关。在保存期间，第一次休眠将尝试更新帖子以匹配该评论，但该评论尚不存在，因此失败。

对您来说更好的工作流程如下。

返回带有所有评论的帖子更有意义，并且只需将新评论附加到已经存在的帖子中。这样，hibernate 将首先创建评论实体，然后将其与已经存在且不会遇到任何问题的帖子相关联。

@PostMapping("/posts/{postId}/comments")
public Post createComment(@PathVariable (value = "postId") Long postId,
                             @Valid @RequestBody Comment comment) {
    Optional<Post> postOpt = postRepository.findById(postId);
      if (postOpt.isPresent()) {
        comment.setPost(postOpt.get()); <----------------
        postOpt.get().getComments().add(comment);
        postRepository.save(postOpt.get());
        return postOpt.get();
      } else {
        throw new ResourceNotFoundException("PostId " + postId + " not found");
      }

   }

Answer 2

我遇到了类似的问题，要解决它，您需要将父对象设置为子对象。 会是这样的

post.getComments().stream().forEach(c -> c.setPost(post));