Conditional “orderby” sort order in LINQ

Question

In LINQ, is it possible to have conditional orderby sort order (ascending vs. descending).

Something like this (not valid code):

bool flag;

(from w          


        

Answer 1

You could try something like the following:

var q = from i in list
         where i.Name = "name"
         select i;
if(foo)
     q = q.OrderBy(o=>o.Name);
else
     q = q.OrderByDescending(o=>o.Name);

Answer 2

Here is a more general solution, that can be used for various conditional lambda expressions without breaking the flow of the expression.

public static IEnumerable<T> IfThenElse<T>(
    this IEnumerable<T> elements,
    Func<bool> condition,
    Func<IEnumerable<T>, IEnumerable<T>> thenPath,
    Func<IEnumerable<T>, IEnumerable<T>> elsePath)
{
    return condition()
        ? thenPath(elements)
        : elsePath(elements);
}

e.g.

var result = widgets
    .Where(w => w.Name.Contains("xyz"))
    .IfThenElse(
        () => flag,
        e => e.OrderBy(w => w.Id),
        e => e.OrderByDescending(w => w.Id));

Answer 3

...Or do it all in one statement

bool flag;

var result = from w in widgets where w.Name.Contains("xyz")
  orderby
    flag ? w.Id : 0,
    flag ? 0 : w.Id descending
  select w;