Since this excellent blog has helped me loads to get to grips with SSIS, I thought I would give my ten pence worth.
I was really frustrated with this - and was determined to stick with using a derived column component (I'd already got through mapping 40 odd fields and didnt want to start again using the script component!).
Anyway, I found a hack to get around this issue.
IF NOT NULL(Col) AND ISNUMERIC(Col) THEN
Result = cLng(Col)
ELSE
Result = 0
END IF
in DTS
equates to:
Result = !ISNULL([Col]) && ((DT_STR,20,1252) [Col] == ((DT_STR,20,1252) (DT_I4) [Col] )) ? (DT_I4) [Col] : 0
All I do convert Col to an int, then back to a string - and compare it to the original string value.
If they are the same then it's a numeric field.
Also, I believe that because I am checking for null before this happens, the IF statement will jump out when a null is found, stopping the cast to an int from failing.
Seems to work fine for me - hope it helps the rest of you!
