U-SQL Substring out of range exception - substring

Question

We are trying to publish data from a table using U-SQL in ADLA. We are using below code to get substring for FirstName, as we want to restrict the length of FirstName to 50 characters.
SELECT (firstName == null || firstName.Length <= 50) ? firstName : firstName.Substring(0, 50) AS FirstName
But, we are getting below error:
E_RUNTIME_USER_EXPRESSION_EVALUATION >
E_RUNTIME_USER_SUBSTRING_OUT_RANGE
When we tried to perform substring using custom .NET Code, we are not getting exception. The job is completing successfully. We are not getting any error rows.
public static string DoSubString(string firstName)
{
string subFirstName;
try
{
subFirstName = (firstName == null || firstName.Length <= 50) ? firstName : firstName.Substring(0, 50);
}
catch(ArgumentOutOfRangeException ae)
{
subFirstName = string.Format("Argument Out of range Error {0} {1}",firstName,ae.Message);
}
catch(Exception Ex)
{
subFirstName = string.Format("Generic Error {0} {1}",firstName, Ex.Message);
}
return subFirstName;
}
We are not able to find out the error row. When we look into Profile.xml, we are not getting row dump.
Inner exception from user expression: \nCurrent row
dump: "
How to find out the error row causing this exception? How to troubleshoot these kinds of issues ?

Answer 1

For testing I used 10 characters, revise for 50.
#table =
SELECT * FROM
( VALUES
("appleJackss"),
("apple Jacks"),
("appleJacks"),
(" "),
(""),
((string)null)
) AS T(word);
#result =
SELECT //Method 1
CASE
WHEN word.Length <= 10 THEN word
ELSE word.Substring(0, 10)
END AS justTen,
// Method 2
(word.Length <= 10) ? word : word.Substring(0, 10) AS anotherTen
FROM #table;
OUTPUT #result
TO "/Temp/Example1.txt"
USING Outputters.Tsv();

Answer 2

We raised an issue with product group. It seems there is some problem with the substring operation in U-SQL. They asked us to apply the below fix for Substring calculation. We tried it and it is working properly.
SELECT (firstName == null || firstName.Length <= 50) ? firstName : firstName.Substring(0, Math.Min(firstName.Length, 50)) AS FirstName