How to return empty string if an object is null?

Question

Here is a snippet of my code:

var link = socials.Where(p => p.type == Facebook).FirstOrDefault().URL;

the problem is that there aren't any social object in the list, FirstOrDefault() return null, and .URL trigger an exception.

How can I avoid this in "one" line with LINQ? Thus, if null return empty "" (or custom even better) string, else .URL?

Solution 1

You can use DefaultIfEmpty with an argument to specify the fallback value:

var link = socials
    .Where(p => p.type == Facebook)
    .Select(p => p.Url)
    .DefaultIfEmpty("")
    .First();

FirstOrDefault is not necessary anymore, it is safe to use First with DefaultIfEmpty.

Solution 2

Another option is to use null coalesce operator

var link = (socials
    .Where(p => p.type == Facebook)
    .Select(p => p.Url)
    .FirstOrDefault()) ?? string.empty;

I understood that string.empty is preferred over "" but that may not be the case - see comment below.

UPDATE In C# 6 there is a null conditional operator (also known as the "Elvis" operator):

var link = socials
    .Where(p => p.type == Facebook)
    .Select(p => p.Url)
    .FirstOrDefault()?.URL ?? string.empty;

A simple example:

stringbuilder sb = null;
// do work
string s = sb?.ToString() ?? "no values found"; 

Solution 3

Using C# 6 you can use a null-conditional operator (?.) to return the URL if the object returned from the LINQ statement isn't null, i.e. if a value was found, or null otherwsie.

var link = socials.Where(p => p.type == Facebook).FirstOrDefault()?.URL;

If you then want to change a null value to an empty string or a custom string then use the null-coalescing operator (??).

var link = socials.Where(p => p.type == Facebook).FirstOrDefault()?.URL ?? "No URL";

It should be noted that this won't make any distinction between whether an object wasn't found or an object was found but had a null URL value.

Comments

[Sirwan Afifi]

you can use .First();

[Tim Schmelter]

@SirwanAfifi: which causes an exception if there is no type==facebook.

[Tim Schmelter]

Why is string.empty preferred over ""? Tha's just a matter of personal preferences. Imo "" is very clear.

[Tim Schmelter]

There's a subtle difference between yours and mine answer. You get String.Empty if there is no type==facebook and also if the first matching Url is null. My approach still yields null in that case.

[Steve]

stackoverflow.com/questions/263191/…

[markzzz]

But DefaultIfEmpty works even if the Select return 0 object? I mean, if the where count is 0, it returns at least one ""?

[Tim Schmelter]

Yes, that's the sole purpose of DefaultIfEmpty. It comes only into play if the sequence contains no elements. Then it uses the default value of the type or - if you use the overload as in my answer - it uses the value provided. So with the same result as if the sequence contained only one element with that value.

[Sagar Khatri]

Saved few additional lines of code and time. Works as expected