Throw exception from SQL Server function to stored procedure - sql

Question

I have stored procedure in SQL Server 2012 say spXample and a scaler-valued function say fXample.
I call a function fXample from spXample.
Can I throw an exception in function and catch it in stored procedure's Catch block and rethrow to the calling C# code?
Update:
The function I wrote like:
CREATE FUNCTION dbo.fXample(#i INT)
RETURNS TINYINT
AS
BEGIN
RETURN (SELECT CASE WHEN #i < 10
THEN THROW 51000,'Xample Exception',1;
ELSE (SELECT #i)
END);
END
GO
I am getting error
Msg 443, Level 16, State 14, Procedure fXample, Line 46 Invalid use of
a side-effecting operator 'THROW' within a function.
How do I write alternative code to achieve above functionality?

Answer 1

You can do this by forcing an error condition when your validation fails, provided that isn't a possible error that might occur naturally. When you know a certain error can only occur when validation has failed, you can handle that in a custom way by checking for that error_number in your catch block. Example in tempdb:
USE tempdb;
GO
CREATE FUNCTION dbo.fXample(#i INT)
RETURNS TINYINT
AS
BEGIN
RETURN (SELECT CASE WHEN #i < 10 -- change this to your "validation failed" condition
THEN 1/0 -- something that will generate an error
ELSE (SELECT #i) -- (you'd have your actual retrieval code here)
END);
END
GO
CREATE PROCEDURE dbo.spXample
#i INT
AS
BEGIN
SET NOCOUNT ON;
BEGIN TRY
SELECT dbo.fXample(#i);
END TRY
BEGIN CATCH
IF ERROR_NUMBER() = 8134 -- divide by zero
BEGIN
THROW 50001, 'Your custom error message.', 1;
-- you can throw any number > 50000 here
END
ELSE -- something else went wrong
BEGIN
THROW; -- throw original error
END
END CATCH
END
GO
Now try it out:
EXEC dbo.spXample #i = 10; -- works fine
EXEC dbo.spXample #i = 6; -- fails validation
EXEC dbo.spXample #i = 256; -- passes validation but overflows return
Results:
----
10
Msg 50001, Level 16, State 1, Procedure spXample, Line 12
Your custom error message.
Msg 220, Level 16, State 2, Procedure spXample, Line 7
Arithmetic overflow error for data type tinyint, value = 256.

Answer 2

/* *** EXAMPLES ***
SELECT dbo.fnDoSomething(500) -- RETURNS TRUE
SELECT dbo.fnDoSomething(5000) -- THROWS ERROR
Msg 245, Level 16, State 1, Line 4
Conversion failed when converting the varchar value
'Function Error - [dbo].[fnDoSomething] - Value is greater than 1000' to data type bit.
*/
CREATE FUNCTION dbo.fnDoSomething
(
#SomeValue INT
)
RETURNS BIT
AS
BEGIN
IF #SomeValue > 1000
BEGIN
DECLARE #FunctionName AS SYSNAME = QUOTENAME(OBJECT_SCHEMA_NAME(##PROCID)) + '.' + QUOTENAME(OBJECT_NAME(##PROCID))
DECLARE #Error AS VARCHAR(200) = 'Function Error - '+ #FunctionName + ' - Value is greater than 1000'
RETURN CONVERT(BIT,#Error)
END
RETURN 1
END
GO

Answer 3

Although this has been solved but I feel I should still share this. As I think it will be a simpler solution:
BEGIN TRY
THROW 60000, 'Error', 1;
END TRY
BEGIN CATCH
THROW
END CATCH

Answer 4

You can also raise an error in the stored procedure if a certain condition is met but the error severity has to be higher than 10 to throw an SQL exception
CREATE PROC test
AS
RAISERROR('the error message', 11, 1);
RETURN
you can access this message later in your catch block as such
try {
testProc.ExecuteNonQuery();
}
catch(SqlException ex)
{
System.Diagnostics.Debug.WriteLine(ex.Message);
}
Output : "the error message"