1. A5: Structured Error Handling in the ABL Phillip Malone Senior Technical Support Engineer

2. © 2008 Progress Software Corporation 2 Structured Error Handling -- Agenda  Overview of the old and new  Catching errors  Raising errors  The FINALLY block  Changes to be aware of

3. © 2008 Progress Software Corporation 3 NO-ERROR / ERROR-STATUS Traditional Error Handling Model Behavior handled at the statement level ON ERROR, UNDO { LEAVE | RETRY | …} Behavior handled locally at the block level RETURN ERROR [error string] Application can return error to its caller

4. © 2008 Progress Software Corporation 4 Failure cases handled in varied and inconsistent ways Errors must be handled locally, do not propagate automatically No way to add additional information to application errors Traditional Error Handling Model

5. © 2008 Progress Software Corporation 5 A Bit About Blocks

6. © 2008 Progress Software Corporation 6 UNDO, ON ERROR RETRY NEXT LEAVE RETURN A Bit About Blocks Outer Block Inner Block

7. © 2008 Progress Software Corporation 7 UNDO, ON ERROR RETRY NEXT LEAVE RETURN A Bit About Blocks Outer Block Inner Block E

8. © 2008 Progress Software Corporation 8 CATCH err AS Progress.Lang.Error Structured Error Handling Model – 10.1C CATCH blocks to handle all error types myError INHERITS Progress.Lang.AppError Ability to create user-defined application errors Facilities to propagate errors up the call stack UNDO, THROW

9. © 2008 Progress Software Corporation 9 Let’s look at the code PROCEDURE ErrorBlock: FOR EACH Customer ON ERROR UNDO, LEAVE: FIND FIRST Order WHERE Order-Num = 1001 NO-ERROR. IF ERROR-STATUS:ERROR THEN MESSAGE ERROR-STATUS:GET-MESSAGE(1). FIND FIRST Order WHERE Order-Num = 1002. END. END PROCEDURE.

10. © 2008 Progress Software Corporation 10 ON ERROR UNDO, RETRY NEXT LEAVE RETURN Catching Errors Enclosing Block Associated Block Catch E

11. © 2008 Progress Software Corporation 11 Let’s look at the code PROCEDURE ErrorBlock: FOR EACH Customer: FIND FIRST Order WHERE Order-Num = 1001. CATCH e AS Progress.Lang.SysError: MESSAGE e:GetMessage(1) VIEW-AS ALERT-BOX. DELETE OBJECT e. END CATCH. END. END PROCEDURE.

12. © 2008 Progress Software Corporation 12 Object Hierarchy Progress.Lang.Object Progress.Lang.ProError Progress.Lang.AppError Progress.Lang.SysError Progress.Lang. SoapFaultError User-Defined Error Objects Progress.Lang. Error >

13. © 2008 Progress Software Corporation 13 Error Objects NumMessages, Severity, CallStack Properties available on ProError GetMessage(), GetMessageNum() Methods available on ProError AddMessage(), RemoveMessage() ReturnValue Additional Methods and Properties on AppError

14. © 2008 Progress Software Corporation 14 ON ERROR UNDO, RETRY LEAVE NEXT RETURN Throwing Errors Enclosing Block Associated Block E THROW

15. © 2008 Progress Software Corporation 15 Throwing Errors ROUTINE-LEVEL ON ERROR UNDO, THROW Overrides default ON ERROR of routine level blocks UNDO, THROW Explicitly throws (or re-throws) an error

16. © 2008 Progress Software Corporation 16 Let’s look at the code PROCEDURE ErrorBlock: FOR EACH Customer ON ERROR UNDO, LEAVE: FIND FIRST Order WHERE Order-Num = 1001 NO-ERROR. IF ERROR-STATUS:ERROR THEN MESSAGE ERROR-STATUS:GET-MESSAGE(1). END. END PROCEDURE.

17. © 2008 Progress Software Corporation 17 Let’s look at the code ROUTINE-LEVEL ON ERROR UNDO, THROW. PROCEDURE ErrorBlock: FOR EACH Customer ON ERROR UNDO, THROW: FIND FIRST Order WHERE Order-Num = 1001. END. END PROCEDURE.

18. © 2008 Progress Software Corporation 18 Caller Enclosing Block Returning Errors Associated Block E RETURN ERROR

19. © 2008 Progress Software Corporation 19 Returning Errors RETURN ERROR [error string] Return a Progress.Lang.AppError with error string RETURN ERROR Returns error of type error-object with

20. © 2008 Progress Software Corporation 20 /* MAIN.P */ RUN ErrorBlock IN hPersProc. CATCH e AS Progress.Lang.AppError: MESSAGE e:GetMessage(1) VIEW-AS ALERT-BOX. DELETE e. END CATCH. PROCEDURE ErrorBlock: FOR EACH Customer ON ERROR UNDO, LEAVE: FIND FIRST Order WHERE Order-Num = 1001 NO-ERROR. IF ERROR-STATUS:ERROR THEN RETURN ERROR NEW OrdNotFoundError(“1001”). END. END PROCEDURE. Let’s look at the code

21. © 2008 Progress Software Corporation 21 A Few Words About NO-ERROR NO-ERROR Continues to suppress errors at the statement level NO-ERROR Can handle errors raised via UNDO, THROW NO-ERROR Converts information from error objects to ERROR-STATUS

22. © 2008 Progress Software Corporation 22 What that means is… NO-ERROR DO ON ERROR CATCH RETURN ERROR UNDO, THROW ERROR condition Generate any error Handle any error

23. © 2008 Progress Software Corporation 23 Enclosing Block Finally Catch Associated Block And FINALLY… Always executes on success or failure

24. © 2008 Progress Software Corporation 24 Let’s look at the code PROCEDURE ErrorBlock: FOR EACH Customer: FIND FIRST Order WHERE Order-Num = 1001. CATCH e AS Progress.Lang.SysError: MESSAGE e:GetMessage(1) VIEW-AS ALERT-BOX. DELETE OBJECT e. END CATCH. FINALLY: /* clean up code */ END FINALLY. END. END PROCEDURE.

25. © 2008 Progress Software Corporation 25 hSrv:CONNECT(…)NO-ERROR. IF ERROR-STATUS:NUM-MESSAGES > 0 THEN: MESSAGE “Connect Failed!” VIEW-AS ALERT-BOX. Change in Behavior With traditional error handling… hSrv:CONNECT(…). CATCH err AS Progress.Lang.SysError: … END CATCH. With structured error handling… Does Not Raise Error Raises Error

26. © 2008 Progress Software Corporation 26 What About User-defined Functions? Q: Will RETURN ERROR in a udf raise error in the caller? A: No. Q: Is there another way to raise error from a udf? A: YES!

27. © 2008 Progress Software Corporation 27 FUNCTION foo RETURNS INTEGER (): RETURN ERROR. END FUNCTION. Raising Error from User-defined Functions With RETURN ERROR… FUNCTION foo RETURNS INTEGER (): UNDO, THROW NEW AcmeError(). END FUNCTION. With structured error handling… Does Not Raise Error in Caller Raises Error in Caller

28. © 2008 Progress Software Corporation 28 In Summary  Uniform model for handling error conditions  More flexibility for application specific errors  Traditional and structured error handling models co-exist

29. © 2008 Progress Software Corporation 29 Related Presentations DEV-12 What’s New in the Object-Oriented ABL DEV-22 Catch Me If You Can – Practical Structured Error Handling DEV-32 Using the Advanced GUI, Structured Error Handling and SonicMQ to Build Semi- Disconnected Point of Sales

30. © 2008 Progress Software Corporation 30 Questions ?

31. © 2008 Progress Software Corporation 31 Thank You

32. © 2008 Progress Software Corporation 32