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

A5: Structured Error Handling in the ABL

Phillip MaloneSenior Technical Support Engineer

© 2008 Progress Software Corporation2

Structured Error Handling -- Agenda

Overview of the old and new Catching errors Raising errors The FINALLY block Changes to be aware of


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


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


A Bit About Blocks


UNDO,ON ERROR

RETRYNEXTLEAVERETURN

A Bit About Blocks

Outer Block

Inner Block


UNDO,ON ERROR

RETRYNEXTLEAVERETURN

A Bit About Blocks

Outer Block

Inner Block

E


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 <error object>


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.


ON ERROR UNDO,

RETRYNEXT LEAVERETURN

Catching Errors

Enclosing Block

Associated Block

Catch E




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.


Object Hierarchy

Progress.Lang.Object

Progress.Lang.ProError

Progress.Lang.AppError Progress.Lang.SysError

Progress.Lang.

SoapFaultError

User-Defined

Error Objects

Progress.Lang.Error

<<interface>>


Error Objects

NumMessages, Severity, CallStack

Properties available on ProError

GetMessage(), GetMessageNum()

Methods available on ProError

AddMessage(), RemoveMessage()

ReturnValue

Additional Methods and Properties on AppError


ON ERROR UNDO,

RETRYLEAVENEXTRETURN

Throwing Errors

Enclosing Block

Associated Block

E

THROW


Throwing Errors

ROUTINE-LEVEL ON ERROR UNDO, THROW

Overrides default ON ERROR of routine level blocks

UNDO, THROW <error object>

Explicitly throws (or re-throws) an error





MESSAGE ERROR-STATUS:GET-MESSAGE(1).

END.

END PROCEDURE.



ROUTINE-LEVEL ON ERROR UNDO, THROW.


FOR EACH Customer ON ERROR UNDO, THROW: FIND FIRST Order WHERE Order-Num = 1001. END. END PROCEDURE.


Caller Enclosing Block

Returning Errors

Associated Block

ERETURN ERROR


Returning Errors

RETURN ERROR [error string]

Return a Progress.Lang.AppError with error string

RETURN ERROR <error object>

Returns error of type error-object with


/* MAIN.P */ RUN ErrorBlock IN hPersProc.

CATCH e AS Progress.Lang.AppError: MESSAGE e:GetMessage(1) VIEW-AS ALERT-BOX. DELETE e. END CATCH.



RETURN ERROR NEW OrdNotFoundError(“1001”). END.

END PROCEDURE.



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


What that means is…

NO-ERROR

DO ON ERROR

CATCH RETURN ERROR

UNDO, THROW

ERROR condition

Generate any error

Handle any error


Enclosing Block

Finally

Catch

Associated Block

And FINALLY…

Always executes on success or

failure




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.


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


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!


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


In Summary

Uniform model for handling error conditions

More flexibility for application specific errors

Traditional and structured error handling models co-exist


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


Questions?


Thank You

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

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