Java Spring REST控制器保存JSON Post

我被什么东西卡住了，经过一天的搜索和尝试，我终于认输了。我有两个基本域名，一个博客帖子和一个作者。为了使这篇文章简短，我省略了一些代码

@Entity
public class Post {

    @Id @GeneratedValue
    private Long id;
    private String title;

    @Column(columnDefinition = "TEXT")
    private String body;

    @Column(columnDefinition = "TEXT")
    private String teaser;

    private String slug;

    @CreatedDate 
    @Temporal(TemporalType.TIMESTAMP)
    private Date postedOn;

    @ManyToOne
    private Author author;

    // getters & setters    
}

@Entity
public class Author {

    @Id
    @GeneratedValue
    private Long id;
    private String firstName;
    private String lastName;
    private String email;

    // getters & setters 
}

控制器看起来像这样

@RestController
@RequestMapping("/posts")
public class PostController {

    private PostService postService;

    @Autowired
    public PostController(PostServiceImpl postService){
        this.postService = postService;
    }

    @RequestMapping( value = "/", method = RequestMethod.GET )
    public Iterable<Post> list(){
        return postService.list();
    }

    @RequestMapping( value = "/", method = RequestMethod.POST )
    public Post create(@RequestBody Post post){
        return postService.save(post);
    }

    @RequestMapping( value = "/{id}", method = RequestMethod.GET )
    public Post read(@PathVariable(value="id") long id){
        return postService.getPost(id);
    }

    @RequestMapping( value = "/{id}", method = RequestMethod.PUT )
    public String update(@PathVariable(value="id") int id){
        return "post.update()";
    }

    @RequestMapping( value = "/{id}", method = RequestMethod.DELETE )
    public String delete(@PathVariable(value="id") int id){
        return "post.delete()";
    }


}

当我尝试发布这个JSON时

{
    "title" : "A new post created from JSON",
    "slug" : "a-new-post",
    "teaser" : "post teaser",
    "body" : "post body",
    "postedOn" : "2015-11-07",
    "author" : {
        "firstName": "Joe",
        "lastName": "Smith",
        "email": "jsmith@gmail.com"
    }
}

我得到以下错误

{
    "timestamp": 1447018768572,
    "status": 500,
    "error": "Internal Server Error",
    "exception": "org.springframework.dao.InvalidDataAccessApiUsageException",
    "message": "org.hibernate.TransientPropertyValueException: object references an unsaved transient instance - save the transient instance before flushing : com.therealdanvega.domain.Post.author -> com.therealdanvega.domain.Author; nested exception is java.lang.IllegalStateException: org.hibernate.TransientPropertyValueException: object references an unsaved transient instance - save the transient instance before flushing : com.therealdanvega.domain.Post.author -> com.therealdanvega.domain.Author",
    "path": "/posts/"
}

---

您首先需要坚持作者。从Post的角度来看，您呈现给它的作者是暂时的，因为它没有id，因此无法在Post和作者之间进行映射

---

因此，创建作者的持久对象，然后将其插入Post实体。

因此，我更新了我的PostService save方法，首先调用authorService.save（Post.Author），结果似乎很好。谢谢我只是好奇，如果我已经知道作者是谁，我会通过什么？也许还有身份证？作者：{“id”：1}我想说的是按姓名或id查询作者，然后使用setter将其附加到帖子上。一个简单的ID也应该足够了，但您可能会遇到同样的问题。因此，在我看来，这将是类似于

Post Post=new Post（）
post.setAuthor（authorService.get（authorId））
//将其余信息设置为
post
/
postService.save（post）
{
    "timestamp": 1447018768572,
    "status": 500,
    "error": "Internal Server Error",
    "exception": "org.springframework.dao.InvalidDataAccessApiUsageException",
    "message": "org.hibernate.TransientPropertyValueException: object references an unsaved transient instance - save the transient instance before flushing : com.therealdanvega.domain.Post.author -> com.therealdanvega.domain.Author; nested exception is java.lang.IllegalStateException: org.hibernate.TransientPropertyValueException: object references an unsaved transient instance - save the transient instance before flushing : com.therealdanvega.domain.Post.author -> com.therealdanvega.domain.Author",
    "path": "/posts/"
}