Question

Is it better to have 2 Where clauses or 1 Where clause with && operator or does it not matter?

list.Where(x => x.Prop1 == value1).Where(x => x.Prop2 == value2).ToList();

Or

list.Where(x => x.Prop1 == value1 && x.Prop2 == value2).ToList();

Answer 1

It’s better to use the second with two tests in a single lambda. It will loop the list only once and call a delegate only half as often. The first version loops the list twice.

Just to be clear, this is the better option:

list.Where(x => x.Prop1 == value1 && x.Prop2 == value2).ToList();

Which can also be written

var results =
   (from x in list
   where x.Prop1 == value1 && x.Prop2 == value2
   select x).ToList();

If you can avoid the .ToList() call and use it as an IEnumerable<T>, you’ll usually get even better perf (unless you read it over and over).