Linq / lambda expressions - linq

Question

Trying something with Linq / Lambda's, but have no idea where to search.
I'm working on some simple sorting in an ASP.net GridView. Here's some sample code:
IQueryable<User> query = (from c in users select c).AsQueryable<User>();
if (isAscending)
{
switch (e.SortExpression)
{
case "Name":
query.OrderBy(c => c.Name);
break;
default:
break;
}
}
else
{
switch (e.SortExpression)
{
case "Name":
query.OrderByDescending(c => c.Name);
break;
default:
break;
}
}
grid.DataSource = query.ToList();
grid.DataBind();
I am, however, unsatisfied with the code as it is very sensitive to errors and requires lots of duplicated code. I'm hoping to solve this using Lambda expressions instead, but I have no idea how. Here's what I would like to go to:
IQueryable<User> query = (from c in users select c).AsQueryable<User>();
var param = null;
switch (e.SortExpression)
{
case "Name":
param = (c => c.Name);
break;
default:
break;
}
if (isAscending)
{
query.OrderBy(param);
}
else
{
query.OrderByDescending(param);
}
grid.DataSource = query.ToList();
grid.DataBind();
Could anyone please help me?
Thanks!

Answer 1

Your code is broken at the moment - you're calling OrderBy/OrderByDescending but not using the result. You need
query = query.OrderBy(param);
etc.
As for conditionally ordering - the problem is that you can't declare the type of param because the type of the ordering key may well vary depending on the sort expression.
As a workaround, you can write your own extension method:
public static IOrderedQueryable<TSource> OrderByWithDirection<TSource, TKey>
(this IQueryable<TSource> source,
Expression<Func<TSource, TKey>> keySelector,
bool ascending)
{
return ascending ? source.OrderBy(keySelector)
: source.OrderByDescending(keySelector);
}
Your code would then become:
IQueryable<User> query = (from c in users select c).AsQueryable<User>();
switch (e.SortExpression)
{
case "Name":
query = query.OrderByWithDirection(c => c.Name, isAscending);
break;
// etc
default:
break;
}
(Why are you calling AsQueryable, by the way?)