Question

This is a strange problem I’m having, I have the following statement:

IEnumerable<CategoryListViewModel> categoryViewModels = categoryRepository.GetAllCategoryViewModels();

This correctly populates with exactly one element.

categoryViewModels.Where(cvm => cvm.CategoryId == localId).Single().Selected = true;

Yet, nothing gets updated, selected remains false. I can verify that the CategoryId and the localId are equal, if I break out:

var something = categoryViewModels.Where(cvm => cvm.CategoryId == localId).Single()

It correctly returns the one viewModel. In fact, if I go in and I set the local variable “something” to Selected = false. It’ll correctly update the local variable.

Am I missing something obvious?

Edit:

public class CategoryListViewModel
{
    public Guid CategoryId { get; set; }

    public string CategoryName { get; set; }

    public bool Selected { get; set; }
}

Answer 1

I think your problem might be that categoryViewModels is actually an IQueryable – so when you enumerate it, then it makes a database call and SELECTs a list from the database.

This means you create a list, and then change selected for one item in that list.

However… next time you enumerate categoryViewModels then this causes another SELECT to occur – and a new list to be fetched into memory.

To fix this, you could try ToList():

IEnumerable<CategoryViewModel> categoryViewModels = categoryRepository.GetAllCategoryViewModels().ToList();

or you could reorganise your code in some other way to ensure only one underlying query is performed.