如何在“movie_id”表中添加user_id和movie_added_by

Question

我已经有一个用户模型了。现在我已经创建了一个movie_added_by电影模型，我的要求是，每当任何现有的用户要添加任何电影时，user_id和_id将存储在表中。

这里，movie_added_by用户模型需要将一个映射到多个，类似地，电影将映射到movie_added_by。

为了更好地理解，您可以参考DB图。

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我真的不知道如何使用hibernate注释

用户模型如下所示：

@Getter
@Setter
public class User {
    
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "user_id", unique = true, nullable = false)
    private Integer user_id;
    
    private String name;    
} 

电影模型是这样的：

@Getter
@Setter
public class Movie implements Serializable
{
    private static final long serialVersionUID = -6790693372846798580L;
 
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "movie_id", unique = true, nullable = false)
    private Integer movie_id;
 
    private String movie_name;
} 

Answer 1

您可能希望在实体之间创建@ManyToMany关系。有两种方法(使用中间表显式创建或由Hibernate创建)。

在简单的方法中，您的实体如下所示：

public class User {
    
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "user_id", unique = true, nullable = false)
    private Integer user_id;
    
    private String name;

    @ManyToMany(cascade = CascadeType.Persist)
    @JoinTable(name="user_movie", 
    joinColumns = {@JoinColumn(name="user_id")},
    inverseJoinColumns = {@JoinColumn(name="movie_id)})
    private Set<Movie> movies = new HashSet<>();
    
} 

public class Movie implements Serializable
{
    private static final long serialVersionUID = -6790693372846798580L;
 
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "movie_id", unique = true, nullable = false)
    private Integer movie_id;
 
    private String movie_name;

    @ManyToMany(cascade = CascadeType.Persist, mappedBy = "movies" //field from the user class responsible for mapping)
    private Set<User> users = new HashSet<>()



} 

因此，基本上在这里，您告诉Hibernate创建一个中间表，并保持在这两个实体的相关id。这里还有几个注意事项：

( a)您可能希望将id变量类型从Integer更改为Long，以防实体增长；

( b)如果使用@Id对列进行注释，则不必在列注释中使用unique=true和nullable = false；

c)记住实现非args构造函数；

( d)记住从equals()、hashCode()和toString()方法中排除关系文件；

还有一种方法，您可以显式地为表保持关系创建一个模型。当您需要在“relationship”表中保存更多数据时，这可能变得非常方便。在这种情况下，您的实体如下所示：

public class User {
    
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "user_id", unique = true, nullable = false)
    private Integer user_id;
    
    private String name;

    @OnetToMany(cascade = CascadeType.PERSIST, mappedBy = "user")
    private Set<AddedMovie> addedMovies = new HashSet<>()
    
}

public class Movie implements Serializable
{
    private static final long serialVersionUID = -6790693372846798580L;
 
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "movie_id", unique = true, nullable = false)
    private Integer movie_id;
 
    private String movie_name;

    @OneToMany(cascade = CascadeType.PERSIST, mappedBy = "movie")
    private Set<AddedMovie> moviesAddedByUser = new HashSet<>();

} 

@Data
@AllArgsConstructor
@NoArgsConstructor
@Builder
@Entity
public class AddedMovie{
    @Id
    @GeneratedValue
    private Long id;
    @ManyToOne(cascade = CascadeType.PERSIST)
    @JoinColumn(name = "user_id")
    private User user;
    @ManyToOne(cascade = CascadeType.PERSIST)
    @JoinColumn(name = "movie_id")
    private Movie movie;

// sine this entity has now its own lifecycle, you can add more fields here
    private Integer rating;
    private LocalDateTime movieAddedOn;
}