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Contents > CFML Reference > ColdFusion Functions > CreateUUID PreviousNext

CreateUUID

Creates a Universally Unique Identifier (UUID). A UUID is a 35-character string representation of a unique 128-bit integer.

A ColdFusion format UUID, in the format xxxxxxxx-xxxx-xxxx-xxxxxxxxxxxxxxxx, where x is a hexadecimal digit (0-9 or A-F). (The character groups are 8-4-4-4-16.)

Other functions

CreateUUID()

The ColdFusion UUID generation algorithm uses the unique time-of-day value, the IEEE 802 Host ID, and a cryptographically strong random number generator to generate UUIDs that conform to the principles laid out in the draft IEEE RFC "UUIDs and GUIDs."

The ColdFusion UUID format is as follows:

xxxxxxxx-xxxx-xxxx-xxxxxxxxxxxxxxxx (8-4-4-16).

This does not conform to the Microsoft/DCE standard, which is as follows:

xxxxxxxx-xxxx-xxxx-xxxxxx-xxxxxxxxxx (8-4-4-4-12)

There are UUID test tools and a user-defined function called CreateGUID, which converts CFML UUIDs to UUID/Microsoft GUID format, available on the web at www.cflib.org.

Use this function to generate a persistent identifier in a distributed environment. To a very high degree of certainty, this function returns a unique value; no other invocation on the same or any other system returns the same value.

UUIDs are used by distributed computing frameworks, such as DCE/RPC, COM+, and CORBA. In ColdFusion, you can use UUIDs as primary table keys for applications in which data is stored in shared databases. In such cases, using numeric keys can cause primary-key constraint violations during table merges. Using UUIDs, you can eliminate these violations.

<h3>CreateUUID Example</h3>
<p> This example uses CreateUUID to generate a UUID when you submit the form. 
You can submit the form more than once. </p>
<!--- Checks whether the form was submitted; if so, creates UUID. --->
<cfif IsDefined("Form.CreateUUID") Is True>
   <hr>
   <p>Your new UUID is: <cfoutput>#CreateUUID()#</cfoutput></p>
</cfif>
<form action = "createuuid.cfm">
<p><input type = "Submit" name = "CreateUUID"> </p>
</form>
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Comments


isaac dealey said on Dec 29, 2003 at 7:29 PM :
See the createuuid clock speed technote at
http://www.macromedia.com/support/coldfusion/ts/documents/createuuid_clock_speed.htm
AdeptDeveloper said on Dec 19, 2004 at 8:30 AM :
The description of the format is incorrect. The documentation states "The character groups are 8-4-4-4-16.", but it's really 8-4-4-16. The incorrect statement would therefore make the UUID a 40 character string instead of a 35 character string.

-Steve
stonecliz said on Mar 20, 2005 at 2:07 AM :
try the follow code
<cfoutput>#CreateUUID()#</cfoutput>
the formate is 8-4-4-16, therefore , it is a 35 character string
IvyClark said on Jul 13, 2005 at 8:56 PM :
I'm a newbie... used CreateUUID() but notice that duplicate IDs occur although clients, sessions, and time at generation is completely different. Now, I've added a check to make sure the UUID generated doesn't exist in the database before I insert the new record. I couldn't find any solutions out there, so thought I post this note, so other newbies that encounter the same problem know that this problem exists. Is there any other way to prevent duplication? Cheers.
No screen name said on Aug 17, 2005 at 3:14 AM :
Re: duplicate UUIDs, note that *certain*substrings* of CreateUUID() may be the same from invocation to invocation: the UUID is based on date, machine ID and a random number, but it isn't hashed to make one UUID different, character by character, from the next and previous ones.

Only the whole UUID will be unique: are you sure you'renot taking a substring to use as a token?
Glizman said on Mar 22, 2006 at 9:08 AM :
The code example needs:

method="post"

in the form tag.

 

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