Linq query in foreach

Question

I want to clear my doubt regarding LINQ . I have code like:

val collection = this.Employees.Where(emp => emp.IsActive)
foreach (var emp in collection)
 {
   // some stuff
 }

Now if I write code like this:

foreach (var emp in this.Employees.Where(emp => emp.IsActive))
 {
   // some stuff
 }

will this.Employees.Where(emp => emp.IsActive) be executed every iteration or it is executed only once?

Only once. Otherwise you would always be processing the 1st record. — H H, Jun 06 '13 at 10:02

score 7 · Accepted Answer · answered Jun 06 '13 at 10:04

You can think of a foreach as this:

foreach (var x in y)
    // ...

as this:

T x;
using (var enumerator = y.GetEnumerator())
{
    while (enumerator.MoveNext())
    {
        x = enumerator.Current;
        // ...
    }
}

so the two pieces of code you showed will have the same effect.

A for however is different:

for (int index = 0; index < s.Length; index++)

Here s.Length will be evaluated on each iteration of the loop.

score 6 · Answer 2 · answered Jun 06 '13 at 10:01

6

It will be executed only once. To the runtime, both statements have the exact same effect.

answered Jun 06 '13 at 10:01

Erik Schierboom

score 0 · Answer 3 · answered Jun 06 '13 at 10:04

0

It will be executed only once...

answered Jun 06 '13 at 10:04

Keren Caelen

This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient [reputation](http://stackoverflow.com/faq#reputation) you will be able to [comment on any post](http://stackoverflow.com/privileges/comment). – fedorqui Jun 06 '13 at 10:22
ok, will remember this next time... Thank you – Keren Caelen Jun 06 '13 at 10:23
By the way it was an automatic comment after reviewing in http://stackoverflow.com/review/low-quality-posts/ – fedorqui Jun 06 '13 at 10:25

3 Answers3