Uniqueidentifier as parameter in SQL Server Function - sql

Question

I have created a Function in SQL Server 2012 that I will use in a Check Constraint on a table.
The function works as expected if I do:
SELECT [dbo].[CheckValidCardnumberForShellTankingen] ('700678036658047691' ,'2925CA00-6DD5-4F9D-AB0E-AA15DBBD388B')
But when I try to set the expression in Check Constraint so:
([dbo].[CheckValidCardnumberForShellTankingen]([Volledig kaartnummer],[RollBackCode])=(1))
I get a Messaage: "Error validating constraint 'CK_MyConstraint'"
I use the Uniqueidentifier in a Where clause and the strange thing is if I replace the parameter with string containing the Uniqueidentifier I dont get this error.
Here is the Function:
-- =============================================
-- Author: Anders Pedersen
-- Create date: 2015-02-13
-- Description: Check of the Cardnumber of a transaction is valid.
-- =============================================
CREATE FUNCTION [dbo].[CheckValidCardnumberForShellTankingen]
(
-- Add the parameters for the function here
#Cardnumber NvarChar(50),
#RollBackCode NvarChar(200)
)
RETURNS BIT
AS
BEGIN
-- Declare the return variable here
DECLARE
#Result BIT
,#ResultLenght BIT
,#ResultPrefix BIT
,#CardLenght INT
,#SupplierID INT
,#UseCardnumber BIT
,#Prefix NvarChar(50)
-- Add the T-SQL statements to compute the return value here
SET #Result = 0
SET #ResultLenght = 0
SET #ResultPrefix = 0
SET #CardLenght = -1
SET #SupplierID = -1
SET #UseCardnumber = 0
SET #Prefix = ''
-- Get the UseCardnumber and the SupplierID
SELECT #UseCardnumber = C.UseCardNumber, #SupplierID = F.SupplierID
FROM Client C INNER JOIN
ClientFileUploads F ON C.ClientID = F.ClientID
WHERE F.RollBackCode = #RollBackCode
--WHERE F.RollBackCode = '2925CA00-6DD5-4F9D-AB0E-AA15DBBD388B'
-- Only carry out the check if the Client use Cards else set the check to True (1)
IF #UseCardnumber = 1
BEGIN
SELECT #CardLenght = [CardNumberLenght], #Prefix = ISNULL([Prefix],'') FROM [dbo].[Supplier] AS S WHERE S.SupplierID = #SupplierID
IF (#CardLenght IS NULL) OR (#CardLenght = 0)
BEGIN
SET #ResultLenght = 1
END
ELSE
BEGIN
IF (LEN(#Cardnumber) - #CardLenght)= 0
BEGIN
SET #ResultLenght = 1
END
ELSE
BEGIN
SET #ResultLenght = 0
END
END
IF SUBSTRING(#Cardnumber, 1, LEN(#Prefix)) = #Prefix
BEGIN
SET #ResultPrefix = 1
END
ELSE
BEGIN
SET #ResultPrefix = 0
END
IF ((#ResultLenght = 1) AND (#ResultPrefix = 1))
BEGIN
SET #Result = 1
END
ELSE
BEGIN
SET #Result = 0
END
END
ELSE
BEGIN
SET #Result = 1
END
-- Return the result of the function
RETURN #Result
END
GO

Answer 1

If #RollBackCode is a uniqueidentifier, I recommend making the parameter a uniqueidentifier and not a varchar.
As Rhys Jones points out, you shouldn't use a UDF in a check constraint.
See
https://dba.stackexchange.com/questions/22297/udf-in-check-constraint-downside
https://social.msdn.microsoft.com/Forums/sqlserver/en-US/078b720f-faac-425c-b51a-33bcecb263d2/check-constraint-with-udf-problem-with-lots-of-data?forum=transactsql
http://sqlblog.com/blogs/tibor_karaszi/archive/2009/12/17/be-careful-with-constraints-calling-udfs.aspx
If you need to check in a trigger and roll back -- SQL Server - After Insert/ For Insert - Rollback