23
Sep
2008
I love FirstOrDefault
I know all of you who are using C# 3.0 (released with .Net 3.5) have found some of the goodness that is in System.Linq. My current favorite is FirstOrDefault. This little extension method returns the first element of a list, or the first element that meets a criteria, or returns the object’s default value. If you have done work with generics, you should be familiar with default already. Default for nullable types is null. Default for value types is…it depends on the type.
Example 1:
Here is my old code:
1: List<string> list = LoadList();
2: if (list.Count > 0)
3: return list[0];
4: else
5: return null;
This is the new code with FirstOrDefault:
1: List<string> list = LoadList();
2: return list.FirstOrDefault();
Example 2:
Old code:
1: List<string> list = LoadList();
2: foreach(var s in list)
3: {
4: if (s == "My special text")
5: {
6: return s;
7: }
8: }
9: return null;
New Code:
1: List<string> list = LoadList();
2: return list.FirstOrDefault( s => s == "My special text");
You read my mind, was thinking about how much I loved this little piece of code last week.
I have caught bugs by using SingleOrDefault(), usually with comments around the usage like “there can never be more than 1 Foo’s matching in this collection,” (whoops)
Dang, trasa beat me to my comment. I’ve had one project in particular where SingleOrDefault() caught some false assumptions about a sproc. On the other hand SingleOrDefault() doesn’t return as soon as an item is found (on IEnumerable) so it might be slightly slower on large collections. Not sure about the execution times of the two methods on LTS. I’m curious now, so I might check it out.
My personal favorite Linq extension methods are of the filtering and aggregate types. I use list.Any(item => item.IsSomethingTrue) and list.Max(item => item.Property) a lot.
Example 1: return list.Count > 0 ? list[0] : null;
Example 2: return list.Find(“whatever”);
or, if List.Find(T item) did not yet exist, return list.Contains(“whatever”) ? “whatever” : null;
Are not all that worse than the FirstOrDefault code, are they?
I think its important to point out that FirstOrDefault or SingleOrDefault are extension methods of IEnumerable, and Enumerate when called.
@Jamie
The example above is using List, so your arguments are fair. However, if you where working with IEnumerable, you would be forced to enumerate somehow before your example would work. (such as calling ToList())
In that case, FirstOrDefault does it all in one shot, is is much simpler, and doesnt force you to copy to the whole collection to a list when all you want is one object.
Learn something new every day. I didn’t know the method could take a lambda…guess I wasnt paying attention. I thought you had to do this:
return list.Where(blah blah).FirstOrDefault();
Nice.
love C# 🙂
myTable.firstOrDefault
or myTable.Take(1).FirstOrDefault ? for select top 1 * from myTable
Rock on. Thanks for explaining this with a clean, simple C# example.
So far i have had 1 trouble with it in .NET CF 3.5
List containing:
aaaaa
aabbb
abbcc
abccc
abcdd
var one = (from p in List where p.StartsWith(“abcd”) select p).FirstOrDefault();
one is null.
How is that possible?