java - 如何在双向多对多映射中添加数据？(这不是添加数据的正常过程)

Question

public class Movies {
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private int movie_id;

        @Column(unique = true, length = 255)
        private String movie_name;

        private String movie_language;

        @ManyToMany(fetch = FetchType.LAZY,cascade = CascadeType.ALL)
        private Set<Actors> actors;

        private String movie_genre;
           //Getter-Setters
    }

    public class Actors {

        @Id
        @GeneratedValue(strategy = GenerationType.AUTO)
        private int actor_id;

        private String actor_name;

        private String actor_industry;

        @ManyToMany(fetch = FetchType.LAZY,cascade = CascadeType.ALL,mappedBy = "actors")
        Set<Movies> movies;

            //Getter-Setters
        }

    /*This is where my logic resides*/

我有两个实体电影和 Actor ，它们具有多对多映射。 如果我添加一部带有 Actor 的电影，我可以在数据库中看到它，并带有映射电影和 Actor 的附加表。

现在假设如果我输入另一部具有相同 Actor 的新电影，它会给我一个错误， Actor 已经存在(这里 Actor 中的 actor_name 和电影中的 movie_name 是唯一的)，

如何在数据库中添加电影，以便它应该在电影表中输入新电影，但如果 Actor 已经存在于类型转换中，它应该简单地将新电影与现有 Actor 映射。

例如:首先输入这个

{
  "movie_name":"Titanic",
  "movie_language":"English",
  "release_year":"1997",
  "movie_genre":"Romance",
  "actors":[
    {
      "actor_name":"Leonardo",
      "actor_industry":"Hollywood"  
    }
  ]
}

现在我想输入第二部电影:

{
  "movie_name":"Once upon a time in hollywood",
  "movie_language":"English",
  "release_year":"2019",
  "movie_genre":"Drama",
  "actors":[
    {
      "actor_name":"Lenardo",
      "actor_industry":"Hollywood"  
    },
    {
      "actor_name":"Brad",
      "actor_industry":"Hollywood"  
    }
  ]
}

:::::这是我添加新电影的方式:::::::

public void addMovie(Movies movie) {
        Movies tempMovie = movieRepository.findByName(movie.getMovie_name());
        if (tempMovie != null) {
            Set<Actors> actors = new HashSet<Actors>();
            actors = movie.getActors();
            for (Actors actors2 : actors) {
                tempMovie.getActors().add(actors2);
            }
            movie = tempMovie;
            movieRepository.save(movie);
        } else {
            System.out.println("############################In else");
            Set<Actors> actors = movie.getActors();
            for (Actors actors2 : actors) {
                System.out.println(actors2.getActor_name());
                Actors actorTemp = actorRepository.findByName(actors2.getActor_name());
                // System.out.println("Id::::"+actorTemp.getActor_id());
                if (actorTemp != null) {
                    System.out.println("Actor is there " + actors2.getActor_name());
                    System.out.println("Before" + actorTemp.getMovies());
                    actorTemp.getMovies().add(movie);
                    System.out.println("After:" + actorTemp.getMovies());
                    movie.getActors().add(actorTemp);
                    System.out.println("Added");
                    movieRepository.save(movie); //If I remove this line,then there's no error,but also no changes in DB.....without this line my new movie won't be persisted.
                } else {
                    System.out.println("Actor is new");
                    movieRepository.save(movie);
                }
            }
        }

    }

Answer 1

我认为您正在寻找类似桥接表或连接表之类的内容，其中包含电影和 Actor 的标识符。这个blog很好地解释了您需要为此场景实现什么。为了避免由于数据库中的重复记录而出现错误，请熟悉 JPA 的合并与持久之间的区别(我假设您由于注释而使用 JPA)。我希望这对您有所帮助，祝您编码愉快!