LINQ: convert .Single() to query notation

Question

So I know the query notation

var word = from s in stringList
           where s.Length == 3
           select s;

is equivalent to the dot notation

var word = stringList
           .Where(s => s.Length == 3)
           .Select(s => s);

But how do you convert this dot notation to a query notation?

var word = wordsList
           .Single(p => p.Id == savedId);

I couldn't find much resources on Google.

Just stick with the dot notation in this case. It is the cleanest, most concise way to convey (to the programmer) what you're trying to do. — Jonathon Reinhart, Jan 17 '14 at 19:38

score 6 · Accepted Answer · edited Jan 17 '14 at 22:53

6

You can't. A lot of LINQ functions can't be used in the query syntax. At best, you can combine both and do something like

var word = (from p in wordsList
            where p.Id == savedId
            select p).Single()

but in the simple case of collection.Single(condition), the "dot notation" seems more readable to me.

There is a list of keywords used by LINQ on MSDN, you can see which functions are integrated into the language from that list.

edited Jan 17 '14 at 22:53

shoftee

answered Jan 17 '14 at 19:34

dee-see

But it will not be translated exactly into `Single(condition)`. – MarcinJuraszek Jan 17 '14 at 19:36
@MarcinJuraszek Well you can add a condition in the `Single` when its needed. – dee-see Jan 17 '14 at 19:37
2

@Vache ...which would be exactly what the OP is asking to convert from. – Jonathon Reinhart Jan 17 '14 at 19:41
1

@JonathonReinhart The condition is in the where. Or did I not understand what you're saying? – dee-see Jan 17 '14 at 19:44
@Vache You said "you can add a condition in the `Single`"... which would result in the exact thing the OP is asking to convert to query notation. – Jonathon Reinhart Jan 17 '14 at 20:06

score 3 · Answer 2 · answered Jan 17 '14 at 19:34

3

Single doesn't have an exact equivalent in query notation.

The best you can do is to wrap your query in parentheses and call .Single yourself.

answered Jan 17 '14 at 19:34

Ben

score 2 · Answer 3 · answered Jan 17 '14 at 19:34

2

The only thing you can do is:

var word = (from w in wordsList
            where w.Id == savedId
            select w).Single();

but It will not be exactly the same. It will be transformed into

var word = wordsList
           .Where(p => p.Id == savedId)
           .Single();

answered Jan 17 '14 at 19:34

MarcinJuraszek

As I see it, `.Where(predicate).Single()` and `.Single(predicate)` are functionally identical, and will exhibit the same runtime performance. – Jonathon Reinhart Jan 17 '14 at 19:37
1

They are functionally identical, but they are not exactly the same. But I'm not sure about the performance. They should be **really, really small difference you should not ever carry about**. – MarcinJuraszek Jan 17 '14 at 19:38
Well [this is very interesting](http://stackoverflow.com/questions/21194750/which-is-faster-singlepredicate-or-wherepredicate-single).... – Jonathon Reinhart Jan 17 '14 at 20:05
Oh, I know why that is. `Single()` throws exception when it sees second item, `Single(predicate)` iterated entire collection even when it sees second matching element earlier! – MarcinJuraszek Jan 17 '14 at 20:09

score 0 · Answer 4 · answered Jan 17 '14 at 19:35

0

Single is not part of the query notation. You could change your first example to the following to achieve what you want:

var word = (from s in stringList where s.Length == 3 select s).Single();

answered Jan 17 '14 at 19:35

Adam Modlin

4 Answers4