if you have a select LINQ query that should only return one result, do you have to have a foreach loop to get the result?
Or is there a better way?
+1
A:
You can just use .First() or .FirstOrDefault() like so:
Foo foo = query.Select(a => a.Name == "foo").FirstOrDefault();
fordan
2009-12-18 18:30:47
If the query "**should** only return one result" Single is more effective as it throws if the query returns more than one, flagging bugs.
Martinho Fernandes
2009-12-18 18:36:07
@Martinho Fernandes You are right, I had never used Single
fordan
2009-12-18 20:41:25
+11
A:
// Will return a default value if no object is found in the DB
db.Table.SingleOrDefault(x => x.something == someParameter);
or
// Will throw an exception if records are not found
db.Table.Single(x => x.something == someParameter);
Thanks to Mehrdad for the comment...both lines have been updated.
If it's possible that your query could result in more than one record being returned, then (as mentioned in comments) Single() and SingleOrDefault() are the wrong methods to call. You would keep the same syntax, but call First() and FirstOrDefault() respectively.
Justin Niessner
2009-12-18 18:30:49
You can replace `.Where(predicate).Single()` with `.Single(predicate)`.
Mehrdad Afshari
2009-12-18 18:33:35
Single() will raise an exception if more than a single item exists in the sequence. If you don't care to throw an exception, you could also use First() or FirstOrDefault().
LBushkin
2009-12-18 18:35:06
@Mehrdad - I made the change, but is there any performance difference between the two? I usually prefer .Where(predicate).Single() because I think it expresses my intent a little clearer.
Justin Niessner
2009-12-18 18:36:32
@Justin: I doubt there's a noticeable performance difference. The expression tree will be slightly more verbose but the resulting SQL should be similar. `SingleOrDefault` has a similar overload too. I prefer these since they are more concise. By the way, `Single` will return the element if it contains **exactly one** element and throws an exception otherwise.
Mehrdad Afshari
2009-12-18 18:39:48
@Justin: You could have a very very minor difference as with the two-method chain you create one extra enumerator object. However, since object creation is pretty fast these days, you'll probably never notice it.
Martinho Fernandes
2009-12-18 18:41:26
@Mehrdad - Since the OP said the query should return only one result, I used `Single()` and `SingleOrDefault()`. If he would've said the query returned multiple results and he only needed the first, I would've suggested `First()` and `FirstOrDefault()`. As for the style, you're probably right. I'm just living back in the SQL-like days.
Justin Niessner
2009-12-18 18:52:04
+4
A:
You can use either First or Single.
First returns the first row, whether there are multiple rows or just the one.
Single expects only one row to be returned, and throws an exception if there are multiple rows.
Single is therefore potentially a better choice if you expect to only have one row, so that you'll see the problem immediately and can troubleshoot it.
Kyralessa
2009-12-18 18:34:32
A:
From all the have have said my addition is the use the Value property after you have a single element if you are using LINQ-to-XML.
And the Select new { *cols* } if it a list or array or table.
Example.
... select new {c.Name, c.Value};
This tip is to enable you get the values.
Colour Blend
2009-12-18 18:50:33