Shortest way to check for null and assign another value if not

Question

I am pulling varchar values out of a DB and want to set the string I am assigning them to as "" if they are null. I'm currently doing it like this:

if (string.IsNullOrEmpty(planRec.approved_by) == true)
  this.approved_by = "";
else
  this.approved_by = planRec.approved_by.toString();

There seems like there should be a way to do this in a single line something like:

this.approved_by = "" || planRec.approved_by.toString();

However I can't find an optimal way to do this. Is there a better way or is what I have the best way to do it?

Abstemious

The == true is superfluous here... – Upsilon

Answer 1

Try this:

this.approved_by = IsNullOrEmpty(planRec.approved_by) ? string.Empty : planRec.approved_by.toString();

You can also use the null-coalescing operator as other have said - since no one has given an example that works with your code here is one:

this.approved_by = planRec.approved_by ?? planRec.approved_by.toString();

But this example only works since a possible value for this.approved_by is the same as one of the potential values that you wish to set it to. For all other cases you will need to use the conditional operator as I showed in my first example.

Thorlay

Doesn't this null coalescing operator throw a nullreference anyways? The way I see this code does the following: if (planRec.approved_by == null) { this.approved_by = planRec.approved_by.toString(); //<= nullref } else { this.approved_by = planRec.approved_by;}. If I'm wrong please point out the error. – Twentieth

@Twentieth is right, the code is broken. Here's a fix using another fun operator: this.approved_by = planRec.approved_by?.toString() ?? ""; <- That's the null-conditional operator, and I don't think it was around when this question was first asked and answered. Hopefully OP sees this, so he can go refactor his 7 year old code, from two jobs ago :) . – Siffre

I could swear I've seen some kind of syntax that lets you assign to an attribute of an object if that object isn't null, like someObject?.someAttribute = value; but I can't seem to find anything like that. – Herb

Answer 2

Starting with C# 8.0, you can use the ??= operator to replace the code of the form

if (variable is null)
{
    variable = expression;
}

with the following code:

variable ??= expression;

More information is here

Zoosporangium

Is there a VB.net version of this? – Chymotrypsin

Be awesome if you could extend this with conditional access as well eg variable1.variable2?.variable3 ??= value; – Gar

This is not exactly as the author asked - more specifically this answers to subject question, but not the question body (author intention). But this is the answer I was looking for, thanks. – Manofwar

Answer 3

You are looking for the C# coalesce operator: ??. This operator takes a left and right argument. If the left hand side of the operator is null or a nullable with no value it will return the right argument. Otherwise it will return the left.

var x = somePossiblyNullValue ?? valueIfNull;

Newborn

This answer does not cover the all cases from the question (only partially). Notice, that there is "string.IsNullOrEmpty". So Empty case is not handled here. – Laellaertes

upvoted because this was the answer I was looking for. (I just needed the null check) – Lafrance

Answer 4

The coalesce operator (??) is what you want, I believe.

Tiphany

Yep...but only because the default is "". – Raveaux

Um, how so? One can use any expression to replace null with.. – Interpreter

Answer 5

My guess is the best you can come up with is

this.approved_by = IsNullOrEmpty(planRec.approved_by) ? string.Empty
                                                      : planRec.approved_by.ToString();

Of course since you're hinting at the fact that approved_by is an object (which cannot equal ""), this would be rewritten as

this.approved_by = (planRec.approved_by ?? string.Empty).ToString();

Haematocryal

Answer 6

With C#6 there is a slightly shorter way for the case where planRec.approved_by is not a string:

this.approved_by = planRec.approved_by?.ToString() ?? "";

Gravely

Answer 7

Use the C# coalesce operator: ??

// if Value is not null, newValue = Value else if Value is null newValue is YournullValue
var newValue = Value ?? YourNullReplacement;

Dendro

Answer 8

To extend @Dave's answer...if planRec.approved_by is already a string

this.approved_by = planRec.approved_by ?? "";

Raveaux

I'm not sure why this answer is the 8th most voted :/ – Whoopee

Finally a correct answer to the question asked. – Cossack

Answer 9

To assign a non-empty variable without repeating the actual variable name (and without assigning anything if variable is null!), you can use a little helper method with a Action parameter:

public static void CallIfNonEmpty(string value, Action<string> action)
{
    if (!string.IsNullOrEmpty(value))
        action(value);
}

And then just use it:

CallIfNonEmpty(this.approved_by, (s) => planRec.approved_by = s);

Checkerbloom

Answer 10

The accepted answer was correct in time, when it was given.

For people still finding this question: Today you can use the ??= Operator.

e.g:

private string _test = null;

private void InitIfNull(){
 _test ??= "Init";
}

Anther

Answer 11

You can also do it in your query, for instance in sql server, google ISNULL and CASE built-in functions.

Overcast

Answer 12

I use extention method SelfChk

static class MyExt {
//Self Check 
 public static void SC(this string you,ref string me)
    {
        me = me ?? you;
    }
}

Then use like

string a = null;
"A".SC(ref a);

Attitudinarian

I guess you mean but not easy to read and understand, is that so? – Attitudinarian

Ups! You are absolutely right: Very short, but NOT easy to read and understand (at least if you are not used to this notation) – Checkerbloom