注释异常：通过引用映射未知的目标实体属性

Question

我不熟悉Hibernate和JPA，正在尝试连接一个电影、评分员和评分的数据库。我一直收到由org.hibernate引起的错误。注释异常：通过引用映射未知目标实体属性：com.stephenalexander.projects.movierecommender.rating.rating。com.stephenalexander.projects.movierecommender.movie.movie.rations中的电影。每个电影对象和每个评级对象都与评级有一个单一的关系。我是这样写的：

评级：

package com.stephenalexander.projects.movierecommender.rating;

import com.stephenalexander.projects.movierecommender.movie.Movie;
import com.stephenalexander.projects.movierecommender.rater.Rater;

import javax.persistence.*;
import java.time.LocalDateTime;
import java.util.Objects;


@Entity
@Table(name="rating")
public class Rating {
    @Column(name = "rating_id")
    private Long ratingId;
    @Column(name = "rating")
    private Double ratingValue;
    private LocalDateTime time;

    @ManyToOne
    @JoinColumn(name = "rater_id", nullable = false)
    private Rater rater;

    @ManyToOne
    @JoinColumn(name = "movie_id", nullable = false)
    private Movie movie;

电影：

package com.stephenalexander.projects.movierecommender.movie;

import com.stephenalexander.projects.movierecommender.rating.Rating;

import javax.persistence.*;
import java.util.List;

@Entity
@Table(name = "movie")
public class Movie {
    @Id
    @GeneratedValue(
            strategy = GenerationType.AUTO
    )

    @Column(name = "movie_id")
    private Integer movieId;
    private String title;
    private int year;
    @Column(name = "posterurl")
    private String posterUrl;
    @Column(name = "runningtime")
    private int runningTime;

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "movie")
    List<Rating> ratings;

评分者：

package com.stephenalexander.projects.movierecommender.rater;

import com.stephenalexander.projects.movierecommender.rating.Rating;

import javax.persistence.*;
import java.util.List;
import java.util.Objects;

@Entity
@Table(name = "rater")
public class Rater {
    @Id
    @GeneratedValue(
            strategy = GenerationType.AUTO
    )
    @Column(name = "rater_id")
    private Long raterId;

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "rater")
    private List<Rating> ratings;

我查看了许多其他帖子，这个错误似乎最常见的原因是mappedBy注释引用了owner类中实例变量的名称以外的其他内容。我相信我做得对，因为Rating类有一个名为rater的变量和一个名为movie的变量。我不确定还有什么可能导致这个错误。非常感谢您的阅读！

编辑：在这里添加我对答案的评论，以澄清我认为这些注释是如何工作的：

据我所知，List

编辑2：我的另一个想法可能是误解......如果我已经在psql数据库中设置了关系，这些符号是不是不必要的？这是多余的吗？我认为这些符号的目的是让我更轻松地在java中导航查询。在我不断尝试编写查询并遇到错误导致我相信我的代码不知道这些表是相关的之后，我被引导到这些定义关系的符号。以下是它们在PostgreSQL中的设置方式：

-----------+-----------------------------+-----------+----------+-------------------------------------------
 rating_id | integer                     |           | not null | nextval('rating_rating_id_seq'::regclass)
 rater_id  | integer                     |           | not null |
 movie_id  | integer                     |           | not null |
 rating    | smallint                    |           |          |
 time      | timestamp without time zone |           |          |
Indexes:
    "rating_pkey" PRIMARY KEY, btree (rating_id)
Foreign-key constraints:
    "rating_movie_id_fkey" FOREIGN KEY (movie_id) REFERENCES movie(movie_id) ON UPDATE CASCADE
    "rating_rater_id_fkey" FOREIGN KEY (rater_id) REFERENCES rater(rater_id) ON UPDATE CASCADE

                Table "public.rater"
  Column  |  Type   | Collation | Nullable | Default
----------+---------+-----------+----------+---------
 rater_id | integer |           | not null |
Indexes:
    "rater_pkey" PRIMARY KEY, btree (rater_id)
Referenced by:
    TABLE "rating" CONSTRAINT "rating_rater_id_fkey" FOREIGN KEY (rater_id) REFERENCES rater(rater_id) ON UPDATE CASCADE

                         Table "public.movie"
   Column    |          Type          | Collation | Nullable | Default
-------------+------------------------+-----------+----------+---------
 movie_id    | integer                |           | not null |
 title       | character varying(100) |           | not null |
 year        | smallint               |           | not null |
 runningtime | smallint               |           | not null |
 posterurl   | character varying(350) |           |          |
Indexes:
    "movie_pkey" PRIMARY KEY, btree (movie_id)
Referenced by:
    TABLE "movies_genres" CONSTRAINT "fk_movie" FOREIGN KEY (movie_id) REFERENCES movie(movie_id)
    TABLE "movies_directors" CONSTRAINT "fk_movie" FOREIGN KEY (movie_id) REFERENCES movie(movie_id)
    TABLE "movies_countries" CONSTRAINT "fk_movie" FOREIGN KEY (movie_id) REFERENCES movie(movie_id)
    TABLE "rating" CONSTRAINT "rating_movie_id_fkey" FOREIGN KEY (movie_id) REFERENCES movie(movie_id) ON UPDATE CASCADE




Answer 1

缺少的是Target etEntity=Rating.class参数到@OneTo很多。所以不同类中的函数注释如下：

电影

@OneToMany(fetch = FetchType.LAZY, targetEntity = Rating.class, mappedBy = "movie")
private List<Rating> ratings

评分员

@OneToMany(fetch = FetchType.LAZY, targetEntity = Rating.class, mappedBy = "rater")
private List<Rating> ratings

评级

@ManyToOne
@JoinColumn(name = "rater_id", nullable = false)
private Rater rater;

@ManyToOne
@JoinColumn(name = "movie_id", nullable = false)
private Movie movie;

感谢所有看过这个的人！

Answer 2

@Column(name = "movie_id")
private Integer movieId;

@ManyToOne
@JoinColumn(name = "movie_id", nullable = false)
private Movie movie;

你在评级和电影中有一个与movie_id相同的专栏。因此存在冲突。

更改其中一个。