Persisting a ManyToMany relationship

danywu · **Joined:** Wed Sep 20, 2006 10:15 pm **Posts:** 12

Hi folks,

I have mapped a ManyToMany relationship and successfully retrieved data from the DB. Now I would like to persist more data into the DB.

Here's what I've done:

in Dog.java:

Code:

    
       @ManyToMany(
            cascade={CascadeType.PERSIST, CascadeType.MERGE},
            mappedBy="dogs",
            targetEntity=Photo.class,
            fetch=FetchType.EAGER
        )
   private List<Photo> photos;
   public List<Photo> getPhotos(){return photos;}
   public void setPhotos(List<Photo> photos){
      this.photos = photos;
   }

in Photo.java

Code:

       @ManyToMany(
            targetEntity=Dog.class,
            cascade={CascadeType.PERSIST, CascadeType.MERGE},
            fetch=FetchType.EAGER
        )
        @JoinTable(
            name="dogphoto",
            joinColumns={@JoinColumn(name="photoId")},
            inverseJoinColumns={@JoinColumn(name="dogId")}
        )
   private List<Dog> dogs;
   public List<Dog> getDogs(){return dogs;}
   public void setDogs(List<Dog> dogs){
      this.dogs = dogs;
   }

And here's how I tried to use it:

Code:

                     HibernateUtil.getSessionFactory().getCurrentSession().beginTransaction();
      IDogDAO dogDao = DAOFactory.DEFAULT.getDogDAO();
                Dog hurley = dogDao.findById(3, false);
           File file = new File("D:\\Dany's Stuff\\My Pictures\\Berners\\Hurley (Luke)\\First Birthday\\Hurley_1st_BDay_Portrait.jpg");
         
      byte[] imageByte = ImageUtil.FileToByteArray(file);
      Photo photo = new Photo();
         
      photo.setImage(imageByte);
      hurley.getPhotos().add(photo);
      photo.getDogs().add(hurley);
      dogDao.makePersistent(hurley);

                HibernateUtil.getSessionFactory().getCurrentSession().getTransaction().commit();

I'm sure I'm not doing it right here - I get a NullPointerException at the line

Code:

photo.getDogs().add(hurley);

Can someone please help me with this? I'm frustratingly close to get it working - or at least that's what I thought...

Thanks,
Dany.

emmanuel · **Posted:** Tue Nov 07, 2006 6:50 pm

Code:

public class Photo {
  private List<Dog> dogs = new ArrayList<Dog>();