Check if Nullable Guid is empty in c#

Question

Quoting from an answer from this question.

Guid is a value type, so a variable of type Guid can't be null to start with.

What then if I see this?

public Nullable<System.Guid> SomeProperty { get; set; }

how should I check if this is null? Like this?

(SomeProperty == null)

or like this?

(SomeProperty == Guid.Empty)

There's an answer to that question that addresses a nullable guid - a.k.a. `Nullable` or `Guid?` — Damien_The_Unbeliever, Jul 17 '13 at 07:52
I think this link would be helpful for you http://stackoverflow.com/questions/676078/which-is-preferred-nullable-hasvalue-or-nullable-null — sagar, Jul 17 '13 at 07:55
**NOTE** - this question is specifc. about Nullabe Guid's... For how to check if a regular `Guid` is empty: http://stackoverflow.com/questions/9837602/why-isnt-there-a-guid-isnullorempty-method — Don Cheadle, Dec 18 '15 at 17:45

Sir l33tname · Accepted Answer · 2019-12-18T12:13:30.143

137

If you want be sure you need to check both

SomeProperty == null || SomeProperty == Guid.Empty

Because it can be null 'Nullable' and it can be an empty GUID something like this {00000000-0000-0000-0000-000000000000}

edited Dec 18 '19 at 12:13

answered Jul 17 '13 at 07:55

Sir l33tname

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2

to confirm: Guid.Empty.ToString() == "00000000-0000-0000-0000-000000000000" – Matt Kemp Apr 09 '15 at 14:30
6

Guid is never null, but it can be Guid.Empty – piris Jul 21 '15 at 09:22
8

Guid itself not but if you read the question it's a Nullable Guid and the hole point of Nullable is that it can be null ^^ – Sir l33tname Jul 21 '15 at 09:31
This is the correct answer; Note that if you're serializing a `Guid` from input, if you use the *non*-nullable variant, `null` will serialize as `Guid.Empty`, which can save you a `null` check here. – zcoop98 Mar 19 '21 at 23:29

score 28 · Answer 2 · edited Jan 26 '22 at 21:58

28

~~SomeProperty.HasValue I think it's what you're looking for.~~

See DevDave's or Sir l33tname's answer instead.

EDIT : btw, you can write System.Guid? instead of Nullable<System.Guid> ;)

edited Jan 26 '22 at 21:58

derekbaker783

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answered Jul 17 '13 at 07:52

dotixx

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this is only the correct answer when using a Nullable Guid. I guess most people use `Guid?` instead of `Guid` – Don Cheadle Dec 18 '15 at 17:39
7

Not sufficient. A null Guid is not the same as an empty Guid (i.e. Guid.Empty). So you not only need to check Guid?.HasValue, you also have to check whether Guid?.Value == Guid.Empty. – Triynko Jul 08 '16 at 19:43
3

As @Triynko has said this answer needs to be updated to also check for Guid.Empty – Sean T Nov 20 '19 at 14:26
This incorrectly answers the question. – derekbaker783 Jan 26 '22 at 21:59

score 19 · Answer 3 · answered Sep 03 '13 at 15:56

19

Note that HasValue will return true for an empty Guid.

bool validGuid = SomeProperty.HasValue && SomeProperty != Guid.Empty;

answered Sep 03 '13 at 15:56

DevDave

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score 4 · Answer 4 · answered Jul 17 '13 at 07:56

4

Check Nullable<T>.HasValue

if(!SomeProperty.HasValue ||SomeProperty.Value == Guid.Empty)
{
 //not valid GUID
}
else
{
 //Valid GUID
}

answered Jul 17 '13 at 07:56

Sriram Sakthivel

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As other people have pointed out : This will indeed tell you if the Guid is null, but beware! It will return true if the Guid has value Guid.Empty. – jeancallisti Sep 29 '22 at 16:42

Mr. Mr. · Answer 5 · 2013-07-17T07:58:50.840

3

You should use the HasValue property:

SomeProperty.HasValue

For example:

if (SomeProperty.HasValue)
{
    // Do Something
}
else
{
    // Do Something Else
}

FYI

public Nullable<System.Guid> SomeProperty { get; set; }

is equivalent to:

public System.Guid? SomeProperty { get; set; }

The MSDN Reference: http://msdn.microsoft.com/en-us/library/sksw8094.aspx

edited Jul 17 '13 at 07:58

answered Jul 17 '13 at 07:53

Mr. Mr.

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As other people have pointed out : This will indeed tell you if the Guid is null, but beware! It will return true if the Guid has value Guid.Empty. – jeancallisti Sep 29 '22 at 16:42

Afshin Teymoori · Answer 6 · 2020-05-31T10:57:28.790

Beginning with C# 7.1, you can use default literal to produce the default value of a type when the compiler can infer the expression type.

Console.Writeline(default(Guid));  
   // ouptut: 00000000-0000-0000-0000-000000000000

Console.WriteLine(default(int));  // output: 0

Console.WriteLine(default(object) is null);  // output: True

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/default

score 3 · Answer 7 · answered May 26 '21 at 10:51

3

You can create a extension method to validate the GUID.

public static class Validate
{
    public static void HasValue(this Guid identity)
    {
        if (identity ==  null || identity == Guid.Empty)
            throw new Exception("The GUID needs a value");
    }
}

And use the exension

    public static void Test()
    {
        var newguid = Guid.NewGuid();

        newguid.HasValue();
    }

answered May 26 '21 at 10:51

Tasso Mello

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I wouldn't go this route. Your method name is a true/false question and therefor it should return a boolean. I doubt there are many codebases where you'd want to throw an exception when checking for a value, especially when a nullable type is perfectly valid to pass in – jhammond Sep 22 '21 at 18:40
1

OK with the general idea of this approach with two strong objections: Like jhammond has said, don't name it "hasSomething" if it's not meant to return a boolean but instead only meant to raise an Exception. Name it "AssertSomething", C++-style. More genrally, don't give a function the same name as a native function of the System. C# already defines its own HasValue for nullable types! – jeancallisti Sep 29 '22 at 16:45

Check if Nullable Guid is empty in c#

7 Answers7