Entityframework . Asenumerable() or . Tolist()?

Question

In one of the projects I picked up I saw the following code, which implements a data listing method of a given entity, but this listing is used only for reading:

/// <summary>
/// Listar todas entidades
/// </summary>
/// <returns></returns>
public IList<T> ListarTodos()
{
    return ctxContexto.Set<T>().ToList();
}

The method works perfectly, my doubt is about performance and good programming practices with Entityframework. A while ago I saw a question here at Sopt that talked about difference between Ienumerable, Iqueryable and Ilist.

Based on the above-mentioned question, I thought "If my method returns a List<T> I will be giving the person who calls the method the possibility to insert or remove items from the list, "which is not correct, since my list is read-only.

List<Cliente> lista = new Servico<Cliente>().ListarTodos();
lista.RemoveAt(0)
lista.Add(new Cliente());

I changed the method return to Ienumerable as below:

/// <summary>
/// Listar todas entidades
/// </summary>
/// <returns></returns>
public IEnumerable<T> ListarTodos()
{
    return ctxContexto.Set<T>().AsEnumerable();
}

The above code also worked, again every time I call the Listed method, if I perform more than one check with the list item in the same code context:

List<Cliente> lista = new Servico<Cliente>().ListarTodos();
int count = lista .Count();
Console.WriteLine(count);
Console.WriteLine(lista .Any());

The message is presented by Resharper.

Possible Multiple enumeration of Ienumerable

This has also been dealt with in a question here from Sopt and I understood why of the same, my doubts are:

What is the best approach in this case?

Some of them will bring me some performance benefit?

Answer 1

What is the best approach in this case?

Continue to use List<>, which is the resolution in memory of an enumeration. An enumeration may be a function or method whose performance is worse.

If you want the list to be read-only (which I don’t understand, because a list can be changed within the flow of a request), you should use AsReadOnly():

/// <summary>
/// Listar todas entidades
/// </summary>
/// <returns></returns>
public IReadOnlyCollection<T> ListarTodos()
{
    return ctxContexto.Set<T>().ToList().AsReadOnly();
}

Some of them will bring me some performance benefit?

The way you’re using it, no. Using repository over repository, in addition to unjustified, brings unnecessary performance penalties.

Answer 2

List is a Class where all these interfaces are implemented:

Ilist, Icollection, Ienumerable, Ienumerable, Ilist, Icollection, Ireadonlylist, Ireadonlycollection

1. For iteration only 1 time with the result, use the Ienumerable or Ireadonlycollection interface
2. For more than one iteration, convert your enumerable to list: .ToList() at the beginning of the scope of the method where it is called the method with Ienumerable return!

I hope I’ve helped!