LinqTOEntities difference beteen Exists and contains

Question

what is the difference between using exists over contains

var s = new int[] { 1, 2, 3, 4, 5 };
dbset.where(x => s.contains(x.id);

or

var s = new int[] { 1, 2, 3, 4, 5 };
dbset.Where(x => s.Exists(y => x.id));

To clarify, [Exists()](http://msdn.microsoft.com/en-us/library/bfed8bca.aspx) is exposed by `List`. Your `s` is an array, not a list. — Frédéric Hamidi, Mar 18 '13 at 16:04

score 3 · Accepted Answer · answered Mar 18 '13 at 16:15

3

Exists is a method of List<T>, there is no such method on array or IEnumerable<T> extensions.
Correct syntax of usage of this method is x => s.Exists(y => y == x.id) (you should pass predicate, i.e. method which returns boolean)
The difference is - Contains supported by Linq to Entities, Exists is not supported.

answered Mar 18 '13 at 16:15

+1, you did much better in explaining the difference between these two methods, than I. But could you also describe the difference between passing a raw value and a predicate? I just think this is crucial in understanding the key difference between these two methods (Because EF supports `Any` instead of `Exists`, so it's not like a big problem\difference here) – Ilya Ivanov Mar 18 '13 at 16:24
@IlyaIvanov sorry, didn't get you here :) Predicate is a part of Exists method signature, difference between passing raw value and predicate is simple - you either call this method with predicate, or your code do not compile – Sergey Berezovskiy Mar 18 '13 at 16:29
Well, for example, you can capture local variable in a predicate and access it in a predicate, thus creating more flexible conditions for comparison. ANYWAY - lets leave it for self study. Speaking about syntax - you answer is perfectly valid :) – Ilya Ivanov Mar 18 '13 at 16:31

1 Answers1