Upgrade from many to many with EF 6

Question

My problem is when I try to update an entity that has a child class that in turn has other children. The structure is this:

public class Diagrama
{
    [Key]
    public int Numero_Diagrama { get; set; }

    public virtual List<Transicao> Transicoes { get; set; }
}

public class Transicao
{
    [Key]
    public int Numero_Transicao { get; set; }

    public int Numero_Diagrama { get; set; }

    public virtual List<Acao> Acoes { get; set; }
}

public class Acao
{
    [Key]
    public int Numero_Acao { get; set; }

    public virtual List<Transicao> Transicoes { get; set; }
}

Diagram for Transition (1-n)

Transition to Actions (n-n)

modelBuilder.Entity<Transicao>()
    .HasMany(s => s.Acoes)
    .WithMany(c => c.Transicoes)
    .Map(cs =>
    {
         cs.MapLeftKey("Numero_Transicao");
         cs.MapRightKey("Numero_Acao");
         cs.ToTable("wrfTransicaoAcoes");
    });

When I try to change the diagram State to Modified it gives error:

System.Invalidoperationexception: 'Attaching an Entity of type 'Acao' failed because Another Entity of the same type already has the same Primary key value. This can happen when using the 'Attach' method or Setting the state of an Entity to 'Unchanged' or 'Modified' if any entities in the Graph have Conflicting key values. This may be because some entities are new and have not yet Received database-generated key values. In this case use the 'Add' method or the 'Added' Entity state to track the Graph and then set the state of non-new entities to 'Unchanged' or 'Modified' as appropriate.'

    public virtual void Atualizar(TEntity obj)
    {
        ValidaEntidade(obj);

        using (Contexto Db = new Contexto())
        {
            Db.Entry(obj).State = EntityState.Modified;
            Db.SaveChanges();
        }
    }

This is happening because I have an Action in 2 different transitions. But I’m only changing the Diagram.

Data structure, already in the database and loaded in the Diagram class:

If I delete the last line of the 49 transition, everything works because it also references the 4 action.

Someone has a light?

Answer 1

The error means that you sent the same object into context Acao twice, in the first object there is no change, and in the second there is change.

If you’re just altering an object Diagrama, no reason to send the object Diagrama with all aggregated records. You send only the object and that’s it.

This suggests that you are using generic repository on top of Entity Framework, which I’ve explained hundreds of times that it’s wrong to use:

public virtual void Atualizar(TEntity obj)
{
    ValidaEntidade(obj);

    using (Contexto Db = new Contexto())
    {
        Db.Entry(obj).State = EntityState.Modified;
        Db.SaveChanges();
    }
}

In addition to being wrong, practice does not allow you to detach from observing the context entities that are not being manipulated (your case).

I don’t know if you’re using ASP.NET MVC. The easy way to solve this in ASP.NET MVC is in ASP.NET MVC Controller, excluding the properties of Binding:

public ActionResult Editar([Bind(Exclude = "Transicoes")] Diagrama diagrama)
{ ... }

If not, the simple way to solve it is by not setting the navigation property Transicoes:

diagrama.Transicoes = null;

Detach all objects from Transicao and Acao context also solves, but the operation takes longer because the Entity Framework tries to save not only the class object Diagrama, but all other aggregated objects:

foreach (var transicao in diagrama.Transicoes)
{
    Db.Entry(transicao).State = EntityState.Detached;
}