C# - Adding condition to func results in stack overflow exception

Question

I have a func as part of specification class which sorts the given iqueryable

Func<IQueryable<T>, IOrderedQueryable<T>>? Sort { get; set; }

When i add more than one condition to the func like below , it results in stack overflow exception.

spec.OrderBy(sc => sc.Case.EndTime).OrderBy(sc => sc.Case.StartTime);

The OrderBy method is implemented like this

public ISpecification<T> OrderBy<TProperty>(Expression<Func<T, TProperty>> property)
    {
        _ = Sort == null ? Sort = items => items.OrderBy(property) : Sort = items => Sort(items).ThenBy(property);
        return this;
    }

Chaining or using separate lines doesn't make a difference.

This problem gets resolved if I assign a new instance of the specification and set it's func, but i don't want to be assigning to a new instance everytime. Please suggest what am i missing here and how to reuse the same instance (if possible).

Answer 1

This is the problematic part:

Sort = items => Sort(items)

That's like writing a method that calls itself.

What you want is to evaluate the existing Sort function, not "the result of the Sort property at the time of evaluation".

I would rewrite the method like this:

public ISpecification<T> OrderBy<TProperty>(Expression<Func<T, TProperty>> property)
{
    var existingSort = Sort;
    Sort = existingSort is null
        ? items => items.OrderBy(property)
        : items => existingSort(items).ThenBy(property);
    return this;
}

(I would also echo D-Shih's comment - this is a somewhat counter-intuitive approach, and counter to normal LINQ. Maybe you have some particular reason to go against LINQ's expectations of immutability and chaining, but it's definitely unusual.)