Please tell me how to validate GUID in .net and it is unique for always?
- 1Guid's are always unique if all the generators play by the rules: blogs.msdn.com/b/oldnewthing/archive/2008/06/27/8659071.aspxDaniel Little– Daniel Little2014-05-18 10:28:01 +00:00Commented May 18, 2014 at 10:28
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8 Answers
Guid's are unique 99.99999999999999999999999999999999% of the time.
It depends on what you mean by validate?
Code to determine that a Guid string is in fact a Guid, is as follows:
private static Regex isGuid = new Regex(@"^(\{){0,1}[0-9a-fA-F]{8}\-[0-9a-fA-F]{4}\-[0-9a-fA-F]{4}\-[0-9a-fA-F]{4}\-[0-9a-fA-F]{12}(\}){0,1}$", RegexOptions.Compiled); internal static bool IsGuid(string candidate, out Guid output) { bool isValid = false; output = Guid.Empty; if(candidate != null) { if (isGuid.IsMatch(candidate)) { output=new Guid(candidate); isValid = true; } } return isValid; } 
3 Comments
João Angelo
+1 for trying not to use exceptions, -1 because a
Guid can have other formats and the current method will throw an exception for the following case: "{230a0f8b-81fb-4052-866e-9ac6a7611c77"
Wim
+1, In .NET 4.0, we'll finally see the introduction of
Guid.TryParse(), which would obviously be preferable to using a Regex. For now though, this is perfectly sufficient and acceptable. connect.microsoft.com/VisualStudio/feedback/details/94072/…
Daniel Little
Guid's are not random, maybe there's a way to also check if they meet these criteria: blogs.msdn.com/b/oldnewthing/archive/2008/06/27/8659071.aspx
2^128 is a very, very large number. It is a billion times larger than the number of picoseconds in the life of the universe. Too large by a long shot to ever validate, the answer is doomed to be "42". Which is the point of using them: you don't have to. If you worry about getting duplicates then you worry for the wrong reason. The odds your machine will be destroyed by a meteor impact are considerably larger.
Duck!
Comments
Here's a non-Regex answer that should be pretty fast:
public static bool IsHex(this char c) { return ((c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F')); } public static bool IsGuid(this string s) { // Length of a proper GUID, without any surrounding braces. const int len_without_braces = 36; // Delimiter for GUID data parts. const char delim = '-'; // Delimiter positions. const int d_0 = 8; const int d_1 = 13; const int d_2 = 18; const int d_3 = 23; // Before Delimiter positions. const int bd_0 = 7; const int bd_1 = 12; const int bd_2 = 17; const int bd_3 = 22; if (s == null) return false; if (s.Length != len_without_braces) return false; if (s[d_0] != delim || s[d_1] != delim || s[d_2] != delim || s[d_3] != delim) return false; for (int i = 0; i < s.Length; i = i + (i == bd_0 || i == bd_1 || i == bd_2 || i == bd_3 ? 2 : 1)) { if (!IsHex(s[i])) return false; } return true; } 
Comments
You cannot validate GUID's uniqueness. You just hope it was generated with a tool that produces unique 16 bytes. As for validation, this simple code might work (assuming you are dealing with GUID's string representation:
bool ValidateGuid(string theGuid) { try { Guid aG = new Guid(theGuid); } catch { return false; } return true; } 
3 Comments
Kyle Rosendo
Thats the easy way out. Remember that Exceptions should be used for exceptional circumstances, not for validating types.
Kerido
@Kyle Rozendo: Yeah, but with Regex, you pretty much limit the format of GUID's string representation. For example, in your code, the formatting is WITH DASHES only.
iGanja
Yeah, we would never want to take "the easy way out" when writing tons of code to do the same thing is so much better... What if this was a unit test? Would it then be acceptable?
this question was already discussed in this post. You may find more interesting details
Comments
In .net 4, you can use this extension method
public static class GuidExtensions { public static bool IsGuid(this string value) { Guid output; return Guid.TryParse(value, out output); } } 
Comments
i wrote a extension for this
public static bool TryParseGuid(this Guid? guidString) { if (guidString != null && guidString != Guid.Empty) { if (Guid.TryParse(guidString.ToString(), out _)) { return true; } else return false; } return false; } 
1 Comment
rsobon
Method name
TryParseGuid would usually suggest that parsing output is returned as out parameter (like Enum.TryParse etc.). Think of renaming this extension method to IsGuidValid or similar, which will clearly indicate that it returns boolIf you're looking for a way to determine if it's the format of the actual .Net Guid type, take a look at this article. A quick regex does the trick.
