ASP.NET MVC Many-to-Many Relationship (Maintaining insertion order)

Question

I've defined two tables in SQL: "Inquerito" and "Pergunta", and a third table "Inquerito_Pergunta" to make the many-to-many relationship. In that last table, the primary key is both the primary key of the Inquerito and the Pergunta.

I'am supposed to add as many as "Perguntas" as I want into an "Inquerito" instance. And, it's important to keep the insertion order, so when I'm showing it to the user it's shown in the same order. A "Pergunta" can also have multiple "Inquerito", but the order doesn't matter in that case.

I'm using MVC 4 Entity Framework and my Models are defined like this:

    public partial class Inquerito
    {
      public Inquerito()
      {
          this.Pergunta = new List<Pergunta>();
      }

      public System.Guid id { get; set; }
      public virtual ICollection<Pergunta> Pergunta { get; set; }
    }


    public partial class Pergunta
    {
      public Pergunta()
      {
        this.Inquerito = new List<Inquerito>();
      }

      public System.Guid id { get; set; }
      public virtual ICollection<Inquerito> Inquerito { get; set; }
    }

As you can see I've already changed the default HashSet to a List.

To save all stuff to the database I do:

    inquerito.Pergunta.Add(pergunta);
    db.Pergunta.Add(pergunta);
    db.Inquerito.Add(inquerito);

The problem is the insertion order is lost.

After adding all "Pergunta" that I want I do:

        // Grava alterações e desconecta da base de dados.
        db.SaveChanges();

        Inquerito inquerito1 = db.Inquerito.Find(inquerito.id);
        if (inquerito1 != null)
        {
            foreach (Pergunta p in inquerito1.Pergunta.ToList())
            {
                System.Diagnostics.Debug.WriteLine("__pergunta: " + p.descricao);
            }
        }

        db = new quest_geralEntities();

        inquerito1 = db.Inquerito.Find(inquerito.id);
        if (inquerito1 != null)
        {
            foreach (Pergunta p in inquerito1.Pergunta.ToList())
            {
                System.Diagnostics.Debug.WriteLine("__pergunta: " + p.descricao);
            }
        }

So, the first time I print all the "Pergunta" linked to that "Inquerito" everything is shown in the right order (insertion order), but when I update the context, with: "new quest_geralEntities()" when I print it again the insertion order is completely lost.

I've been struggling with this problem for several hours now and I can't find a solution. I hope I've been clear enough to be helped.

Thanks.

Answer 1

If you want to maintain insertion order, I recommend using a field containing an int that increments. You can add an int identity column without it being the primary key and use that column to sort on, maintaining your insertion order.

Answer 2

You can try to change the property type of your relation :

public virtual IList<Inquerito> Inquerito { get; set; }
public virtual IList<Pergunta> Pergunta { get; set; }

You'll need to regenerate the database schema. I'm not sure if it's working on EF, but in NHibernate, it works.

Hope it helps !