Question

When I am trying to add a given image to the same destination city twice, I get the following exception:

NonUniqueObjectException: a different object with the same identifier value was already associated with the session: [org.wah.model.ImageEntity#7]

This is good, since I wouldn’t want duplicates. I try to prevent this from happening in code:

public void addImageToDestination(int idDestination, String imageFileName){
    Destination destination = (Destination) getEntity(idDestination);

    ImageEntityDAO imageDao = new ImageEntityDAO();
    ImageEntity image = imageDao.getImage(imageFileName);

    if(image == null)
        image = new ImageEntity(imageFileName);
    else if(destination.getImages().contains(image)){
        return;
    }

    session.beginTransaction();
        destination.getImages().add(image);
    session.getTransaction().commit();
}

The else-if construct tries to identify if it already exists, then do nothing about it and return as is. However, the else-if condition never evaluates to TRUE and session code is run, yielding the NonUniqueObjectException.

How can I prevent this from happening ?

Answer 1

If you mean that destination.getImages().contains(image) never evaluates to true and should if two ImageEntities have the same city, you should override ImageEntity‘s equals-method:

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;

    ImageEntity that = (ImageEntity) o;

    if (city != null ? !city.equals(that.city) : that.city != null) return false;

    return true;
}