Doubt with Codefirst Entityframework

Question

I’m starting in Entity Framework and I have a question regarding Codefirst. Why I have to use as virtual some properties like the example below?

[Table("Grupo")]
public class Grupo
{
   public int ID { get; set; }
   [Required(ErrorMessage="Nome não pode ser branco.")]
   public string Nome { get; set; }

   public virtual IQueryable<Produto> Produtos { get; set;}
}

Answer 1

For two reasons:

1. Because it is the Entity Framework that assembles this object for you;
2. Because it is not necessarily a list or a collection. It can be a Dynamic Proxy, which makes the lazy loading procedure of the Framework. I explain it here and also here

This is incorrect:

public virtual IQueryable<Produto> Produtos { get; set; }

IQueryable<> is an object that can evaluate a list, not an actual list. This is explained in more detail here.

The correct is:

public virtual ICollection<Produto> Produtos { get; set; }