How can I cast a System.Guid to a string in C#

Question

I have the following field definition in a class:

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

I have another class with the following:

   public string GlobalId { get; set; }

I would like to put the value of from the field with type System.Guid into the string.

I tried to do this here:

        var questionIds = _questionsRepository.GetAll()
            .Where(m => m.Problem != null &&
            m.Problem.SubTopic != null &&
            m.Problem.SubTopic.Topic != null &&
            m.Problem.SubTopic.Topic.SubjectId == 1)
            .Select(m => new QuestionHeader { GlobalId = (string) m.GlobalId })
            .ToList();
        return questionIds;

But it's giving me an error saying:

   Cannot convert type 'System.Guid?' to 'string'

Can someone tell me how I could do this?

Please look at the docs for [Nullable(T).ToString](http://msdn.microsoft.com/en-us/library/9hd15ket(v=vs.110).aspx) — Steve, Dec 26 '13 at 13:39
I'd recommend you to read some basic c# tutorials. you'll enjoy understand the reasoning behind a lot of "weird errors" — Letterman, Dec 26 '13 at 14:03

score 10 · Accepted Answer · answered Dec 26 '13 at 13:37

10

You can get the string representation of the GUID by calling ToString() on it.

As your GUID is nullable, check if it's null before calling ToString():

string myString = guid.HasValue ? guid.Value.ToString() : "default string value";

answered Dec 26 '13 at 13:37

ken2k

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3

According to http://stackoverflow.com/questions/2449008/nullable-tostring, there is no need if you want to represent no-value as empty string. – Euphoric Dec 26 '13 at 13:38
Well, this answer is still a good way to do it if one wants to have a default value. – DarkWanderer Dec 26 '13 at 13:41
@Euphoric @Euphoric True, but as you said it implies you get `string.Empty` in case it's null (and I don't know what the OP wants as a default value). – ken2k Dec 26 '13 at 13:42

score 3 · Answer 2 · answered Dec 26 '13 at 13:36

3

You don't cast to string. You use ToString() method.

Like this:

GlobalId = m.GlobalId.ToString()

answered Dec 26 '13 at 13:36

Euphoric

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The Guid is nullable, you should check if it is null. – anar khalilov Dec 26 '13 at 14:34

Guru Stron · Answer 3 · 2013-12-26T13:42:40.937

3

Just use ToString() method

Guid? g = null;    
string s = g.ToString();

in case of null it will return String.Empty otherwise you'll get string representation of your Guid

edited Dec 26 '13 at 13:42

answered Dec 26 '13 at 13:37

Guru Stron

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Dalorzo · Answer 4 · 2019-08-22T12:16:29.817

3

You can convert a Guid with .ToString():

Guid gid = Guid.NewGuid();

string myID = gid.ToString();

Or using

Convert.ToString

Like:

Guid gid = Guid.NewGuid();

string myID = Convert.ToString(gid);

edited Aug 22 '19 at 12:16

answered Dec 26 '13 at 13:40

Dalorzo

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score 2 · Answer 5 · answered Dec 26 '13 at 13:37

2

Use Convert.ToString instead of (string)

GlobalId =  Convert.ToString(m.GlobalId)

answered Dec 26 '13 at 13:37

Selman Genç

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score 1 · Answer 6 · answered Dec 26 '13 at 13:37

1

GlobalId = m.GlobalId.ToString()

answered Dec 26 '13 at 13:37

Denis

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score 1 · Answer 7 · answered Dec 26 '13 at 13:38

1

string Id = Guid.NewGuid().ToString();

answered Dec 26 '13 at 13:38

Anarion

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How can I cast a System.Guid to a string in C#

7 Answers7