如何在具有许多一对多关系的休眠状态下添加数据

Question

I am having a Song class which has one-to-many relationship with other 3 classes - Album,Genre,Login. These are my POJO classes:

   @Entity  
   @Table(name = "songs")  
   public class Song implements Serializable {  
    @Id  
    @GeneratedValue  
    @Column(name = "song_id")  
    private int songId;  

    @OneToOne(cascade = CascadeType.ALL)  
    @JoinTable(name = "albums_songs_mapping", joinColumns = @JoinColumn(name = "song_id", 
    referencedColumnName = "song_id"), inverseJoinColumns = @JoinColumn(name = 
    "album_id", referencedColumnName = "album_id"))  
    private Album album;  

    @Column(name = "title", nullable = false)  
    private String title;  

    @Column(name = "rating")  
    private int rating;  

    @Column(name = "artists")  
    private String artist;  

    @Column(name = "composer")  
    private String composer;  

    @OneToOne(cascade = CascadeType.ALL)  
    @JoinTable(name = "genre_songs_mapping", joinColumns = @JoinColumn(name = "song_id", 
    referencedColumnName = "song_id"), inverseJoinColumns = @JoinColumn(name =  
    "genre_id", referencedColumnName = "genre_id"))  
    private Genre genre;  
}  

@Entity  
@Table(name = "albums")  
public class Album {  

    @Id  
    @GeneratedValue  
    @Column(name = "album_id")  
    private int albumId;  

    @Column(name = "album_name", length = 250)  
    private String albumName;  

    @OneToMany(cascade=CascadeType.ALL)   
    @JoinTable(name = "albums_songs_mapping", joinColumns = @JoinColumn(name = 
    "album_id", referencedColumnName = "album_id"), inverseJoinColumns = @JoinColumn(name 
    = "song_id", referencedColumnName = "song_id"))  
    private List<Song> songs;  
}  


@Entity  
@Table(name = "genre")  
public class Genre {  

    @Id  
    @GeneratedValue  
    @Column(name = "genre_id")  
    private int genreId;  

    @Column(name = "genre_name", length = 250)  
    private String genreName;  

    @OneToMany(cascade=CascadeType.ALL)   
    @JoinTable(name = "genre_songs_mapping", joinColumns = @JoinColumn(name = "genre_id", 
    referencedColumnName = "genre_id"), inverseJoinColumns = @JoinColumn(name = 
    "song_id",referencedColumnName = "song_id"))  
    private List<Song> songs;  
}  

@Entity  
@Table(name = "login", uniqueConstraints = {@UniqueConstraint(columnNames = 
{"user_name"})})  
public class Login {  

    @Id  
    @GeneratedValue  
    @Column(name = "user_id")  
    private int userId;  

    @Column(name = "user_name", nullable=false )  
    private String userName;  

    @Column(name = "password", nullable=false )  
    private String password;  

    @ManyToMany  
    @JoinTable(name = "user_songs_mapping", joinColumns = @JoinColumn(name = " user_id", 
    referencedColumnName = "user_id"), inverseJoinColumns = @JoinColumn(name = "song_id", 
    referencedColumnName = "song_id"))  
    private List<Song> songs;  
}  

I have tried this method in my service . But it is not working. There aren't any errors either. Please help me.

public void addSong(Song song, int userId) throws Exception {  

        Session session = HibernateUtil.getSessionFactory().openSession();  

        try {  

            session.beginTransaction();  
            List<Song> songs = new ArrayList<Song>();  
            songs.add(song);  
            Genre genre = song.getGenre();  
            Album album = song.getAlbum();  
            genre.setSongs(songs);  
            album.setSongs(songs);  
            Login login = new Login();  
            login.setUserId(userId);  
            login.setSongs(songs);  
            session.saveOrUpdate(genre);  
            session.saveOrUpdate(album);  
            session.saveOrUpdate(login);  

            session.getTransaction().commit();  
        } catch (HibernateException e) {  
            if (session.getTransaction() != null) {  
                session.getTransaction().rollback();  
            }  
        } finally {  
            session.close();  
        }  


    }  

Answer 1

Your Login entity has userName and password attributes which aren't nullable, yet you don't set them when you create and save the Login instance, which is probably the cause of the MysqlConstraintViolationException you mention in your comment.

To fix it just set the username and password before persisting your entity.

Hope this helps. If it doesn't please post the whole stack trace of the exception so we can better determine what exactly fails in your code.