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Currently, a new user can register using the an username that has been taken by another user. This is a bug as multiple users can have the same username. Therefore, we won't be able to identify who's who.

Therefore, we need to update our UserController class and:

1. Check if a new user is trying to register with a username that has been previously registered
2. If yes, flash an error on the user registration page saying that the username has been previously registered.

Currently, you cannot create two images with the same title, even thought this should be allowed. However, the server will throw an error if you try to create two images with the same title, and then navigate to one of the images.

Reproduction Step:

1. Create a new image with a title
2. Create a second image with the same title as the first image
3. You'll see a server error if you try to navigate to either the first or second image

The issue:

1. The ImageManager class retrieves an image by its title in the "getImageByTitle" method. Please see the following code in the ImageManager class:

    public Image getImageByTitle(final String title) {
        Session session = openSession();

        try {
            Image image = (Image)session.createCriteria(Image.class)
                    .add(Restrictions.eq("title", title))
                    .uniqueResult(); // retrieves only 1 image
            commitSession(session);

            return image;
        } catch(HibernateException e) {
            System.out.println("unable to retrieve an image from database by its title");
        }

        return null;
    }

2. As you can see in the getImageByTitle method, we uses a Hibernate method called "uniqueResult"
3. the uniqueResult method will throw an exception if there is more than than one matching result. Please see the documentation at: https://docs.jboss.org/hibernate/orm/3.2/api/org/hibernate/Query.html#uniqueResult()

Possible Solution:

• Instead of retrieving an image by its title, we should retrieve an image by a more unique identifier, such as the image's table id.
• In addition, we need to update the ImageController so that:
  • an image's url includes its unique identifier
  • the image controller will then use that unique identifier to retrieve an image. This will require an update to both the ImageServer and ImageManager classes.