Spring REST 控制器保存 JSON 帖子

Question

我被一些事情困住了，经过一天的搜索和尝试不同的事情，我认输了。我有 2 个基本域，一个博客文章和一个作者。我留下了一些代码来保持这篇文章的简短。

@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 
}

控制器长这样

@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()";
    }


}

所有服务方法所做的就是获取 Post POJO 并调用存储库上的保存方法。这是我的问题，我什至觉得问它很愚蠢。当我从没有作者（null）的 Postman 发布 JSON 时，一切正常。我只是不确定如何用新作者或现有作者发布 json 对象。

这行得通

{
    "title" : "A new post created from JSON",
    "slug" : "a-new-post",
    "teaser" : "post teaser",
    "body" : "post body",
    "postedOn" : "2015-11-07"
}

当我尝试发布此 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"
    }
}

我收到以下错误

{
    "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/"
}

Answer 1

您首先需要持久化作者。从 Post 的角度来看，您呈现给它的 Author 是 Transient，因为它没有 id，因此 Post 和 Author 之间无法进行映射。

所以创建一个作者的持久对象，然后将其插入到 Post 实体中。