Question

I’m writing an ASP.net MVC3 application using Entity Framework Code First and SqlCe4.

I have been designing several models, and found one that is turning out to be interesting. This is what I have so far:

public class Preference
    {
        public int PreferenceId { get; set; }

        [Required]
        public int StudentId { get; set; }
        public virtual Student Student { get; set; }

        [Required]
        public int PresentationId { get; set; }
        public virtual Presentation Presentation { get; set; }

        [Required]
        public int Rank { get; set; }
    }

I however, need a unique constraint or index, because for a particular student, I want them to have to have a list of preferences, but the PresentationId needs to be unique for each student. Is there a way to do this via Code First or some validation attribute?

This sounds like I’m going down the branch of a many to many relationship with the Preference object being an intermediary, to add the Rank property. However, I can’t seem to find how to make sure that the values are unique. Is the best way really to manually just add a unique index to the database outside of EF?

Answer 1

Going with what Eranga was saying, I ended up making it work similarly, but like this:

I used the following code in my DataContext class:

public class StudentRegistrationContext : DbContext
{
    public StudentRegistrationContext()
    {
        Database.SetInitializer(new StudentRegistrationDatabaseInitializer());
    }

    public DbSet<Student> Students { get; set; }
    public DbSet<Teacher> Teachers { get; set; }
    public DbSet<Presenter> Presenters { get; set; }
    public DbSet<Presentation> Presentations { get; set; }
}

In the Database Initializer class, I used the following:

public class StudentRegistrationDatabaseInitializer : DropCreateDatabaseIfModelChanges<StudentRegistrationContext>
{
    protected override void Seed(StudentRegistrationContext context)
    {
        base.Seed(context);
        context.Database.ExecuteSqlCommand("CREATE UNIQUE INDEX UX_Preferences_StudentId_PresentationId ON Preferences (StudentId, PresentationId)");
    }
}