java如何插入具有多对多关系的实体？

Question

我正在使用Spring框架。我有两个实体，电影和演员，所以一部电影可以有很多演员，一个演员可以在很多电影中扮演。以下是我们的课程：

import java.util.List;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;

@Entity
public class Actor {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private String surname;
    private String age;

    @ManyToMany
    @JoinTable(name = "movie_actor")
    private List<Movie> movies;

    public Actor(String name, String surname, String age) {
        this.name = name;
        this.surname = surname;
        this.age = age;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSurname() {
        return surname;
    }

    public void setSurname(String surname) {
        this.surname = surname;
    }

    public String getAge() {
        return age;
    }

    public void setAge(String age) {
        this.age = age;
    }

    public List<Movie> getMovies() {
        return movies;
    }

    public void setMovies(List<Movie> movies) {
        this.movies = movies;
    }   
}

import java.util.List;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.ManyToMany;

@Entity
public class Movie {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String title;
    private String genre;
    private String year;

    @ManyToMany(mappedBy = "movies")
    private List<Actor> actors;

    public Movie(String title, String genre, String year, List<Actor> actors) {
        this.title = title;
        this.genre = genre;
        this.year = year;
        this.actors = actors;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getGenre() {
        return genre;
    }

    public void setGenre(String genre) {
        this.genre = genre;
    }

    public String getYear() {
        return year;
    }

    public void setYear(String year) {
        this.year = year;
    }

    public List<Actor> getActors() {
        return actors;
    }

    public void setActors(List<Actor> actors) {
        this.actors = actors;
    }
}

我使用@manytomy注释来定义它们之间的关系

在这里，我在H2中有一个表演员，有ID、年龄、姓名和姓氏列，表电影有ID、流派、标题和年份，还有一个新的表电影演员，因为有演员ID和电影ID列的注释。直到现在，一切似乎都很好

现在，如果我保存一部电影（我已经为这两个实体实现了服务和存储库扩展jpaRepository）：

@GetMapping("/create")
public void create() {
        Actor actor1 = new Actor("Pedro", "Perez", "40");
        Actor actor2 = new Actor("Alfredo", "Mora", "25");
        Actor actor3 = new Actor("Juan", "Martinez", "20");
        Actor actor4 = new Actor("Mario", "Arenas", "30");

        List<Actor> actorList = new ArrayList<>();
        actorList.add(actor1);
        actorList.add(actor2);
        actorList.add(actor3);
        actorList.add(actor4);

        Movie movie = new Movie("Titanic", "Drama", "1984", actorList);

        movieService.create(movie);
    }

（我知道这不是一个get请求，只是为了检查一部电影是否被正确保存，只是为了访问端点）我得到的是，在表MONIVE中，4列被正确添加，但ACTOR和movie_ACTOR都没有完成，所以actorList被ommited，这两个表是空的。为什么会发生这种情况，我该如何解决

非常感谢你的帮助

Answer 1

也许您在服务方法中实现了类似的东西（您没有显示），但我假设它丢失了：您没有cascade任何东西（分别保存另一个类的对象）。您应该将@ManyToMany注释更改为@ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})。这将导致级联合并和持久化操作（保存新对象或任何更改将导致自动更新另一个对象）

还考虑为列表添加适当的添加和移除方法，如在这个article和良好^ ^ a3}中所描述的。

一般来说，你可以在Vlad Mihalcea页面上找到关于Hibernate相关问题的非常好的描述

更新：基于@Alan Hay帖子的实施

模型

@Entity
public class Actor {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private String surname;
    private String age;

    @ManyToMany
    @JoinTable(name = "movie_actor")
    private List<Movie> movies = new ArrayList<>();

    public void addMovie(Movie movie) {
        movies.add(movie);
        movie.getActors().add(this);
    }

    public void removeMovie(Movie movie) {
        movies.remove(movie);
        movie.getActors().remove(this);
    }

    // Constructors, getters and setters...

    // Equals and hashCode methods a la 
    // https://vladmihalcea.com/how-to-implement-equals-and-hashcode-using-the-jpa-entity-identifier/
}

@Entity
public class Movie {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String title;
    private String genre;
    private String year;

    @ManyToMany(mappedBy = "movies", cascade = {CascadeType.PERSIST, CascadeType.MERGE})
    private List<Actor> actors;

    public Movie(String title, String genre, String year, List<Actor> actors) {
        this.title = title;
        this.genre = genre;
        this.year = year;
        actors.forEach(a -> a.addMovie(this));
    }

    // Getters and setters...
}

创建方法

@GetMapping("/create")
public void create() {
    Actor actor1 = new Actor("Pedro", "Perez", "40");
    Actor actor2 = new Actor("Alfredo", "Mora", "25");
    Actor actor3 = new Actor("Juan", "Martinez", "20");
    Actor actor4 = new Actor("Mario", "Arenas", "30");

    List<Actor> actorList = new ArrayList<>();
    actorList.add(actor1);
    actorList.add(actor2);
    actorList.add(actor3);
    actorList.add(actor4);

    Movie movie = new Movie("Titanic", "Drama", "1984", actorList);

    movieService.create(movie);
}