When to instantiate the Icollection

Question

I’m reviewing some programming approaches and falls into a dilemma with regards to where we should instantiate our navigation properties from EF ICollection.

Many cases I see that the personal instance them in the builder, this would be a good practice?

In a few cases I see examples that instantiate only when really necessary, which in my view would be a more correct approach.

So, taking the example of the entity Pais that has a list of Estados

Entidade Pais

[Table("Paises")]
[DisplayColumn("Nome")]
public class Pais : Entidade
{
    public Pais()
    {
        Estados = new HashSet<Estado>();
    }

    [Key]
    public Guid PaisId { get; set; }

    [Required]
    [StringLength(200)]
    public string Nome { get; set; }

    [Required]
    [StringLength(3)]
    public string Sigla { get; set; }

    public ICollection<Estado> Estados { get; set; }
}

State entity

[Table("Estados")]
    [DisplayColumn("Nome")]
    public class Estado : Entidade
    {
        [Key]
        public Guid EstadoId { get; set; }

        public Guid PaisId { get; set; }

        [Required]
        [StringLength(200)]
        public String Nome { get; set; }

        [Required]
        [StringLength(2)]
        public String Sigla { get; set; }

        public virtual Pais Pais { get; set; }

        public ICollection<Cidade> Cidades { get; set; }
    }

In the first approach I see in the parent builder the creation of a HashSet

public Pais()
{
    Estados = new HashSet<Estado>();
}

In another approach I see only at the time of use, as shown by the following example

pais = new Pais();
if (pais.Estados == null)
    pais.Estados = new List<Estado>();

pais.Estados.Add(new Estado() { Sigla = "RS", Nome = "Rio Grande do Sul" });

In the latter case, if the creation of the ICollection<Estado> were in the entity Pais, would not need the if to check whether the object Estados is null, simply add more items to the collection.

Answer 1

I think the best approach is to check if it is null. I don’t usually instantiate collections as in the first approach.

1. Somewhere in the program flow can cause the state of the "States" property to be null. You can guarantee that this will not happen?

2. For example if you use Resharper he will suggest you to check for null.

3. If you’re not always going to use it, there’s no point in making room for the collection.

4. With the Entity Framework, if you use Include(), or Lazy Loading you have no reason to instantiate "States" in the Country Builder.

5. Still with Entity Framework, in a separate scope, you can create a State instance, just pass the country code and add to the database without adding inside the country collection.