Re: Functions, transactions and RETURN

Hate to reply to my own posts, but I thought the solution I've come
across may help others with problems implementing savepoints and
transactions in functions.

This function implements rollbacks whilst still returning a valid row
instead of an exception. A temporary variable is used to get around the
ugly lack of SAVEPOINTs.

----------------------------------------------------------------------
CREATE OR REPLACE FUNCTION tr_addcoursearea(employeeno, coursearea)
RETURNS int4 AS
$BODY$DECLARE
transid int4;
errcode int4;
BEGIN
-- Setup default return code. This is used if we hit an
-- exception that we didn't throw.
SELECT -32767 into errcode; -- E_UNKNOWN

LOCK TABLE backend.courseareas IN ACCESS EXCLUSIVE MODE;

-- Access to administrators only
IF NOT tt_user_access(actor, 'a') THEN
SELECT -1 into errcode; -- Return E_NO_ACCESS
RAISE EXCEPTION 'User % does not have access.', actor;
END IF;

-- Check if there are any active course areas with
-- the given name. We do not allow duplicate names..
-- confusion may abound.
IF tt_coursearea_name_active(area) THEN
SELECT -2001 INTO errcode; -- E_DUP_COURSEAREA
RAISE EXCEPTION 'Course area "%" already exists.', area;
END IF;

-- Grab a transaction ID
SELECT tt_acquire_transaction(actor, 'tr_addcourse') INTO transid;
IF transid < 0 THEN
SELECT transid into errcode; -- Return the error code.
RAISE EXCEPTION 'Could not acquire transaction.';
END IF;

-- Insert the row
INSERT INTO backend.courseareas
(transactionid, active, caname)
VALUES (transid, TRUE, area);

RETURN 0; -- SUCCESS

EXCEPTION
WHEN RAISE_EXCEPTION THEN
RETURN errcode;

WHEN OTHERS THEN
RETURN -32767; -- E_UNKNOWN

END;$BODY$
LANGUAGE 'plpgsql' VOLATILE SECURITY DEFINER;
----------------------------------------------------------------------

Best regards,

Ben Stewart

--
Robert Bosch (Australia) Pty. Ltd.
Engineering Quality Services, Student Software Engineer (RBAU/EQS4)
Locked Bag 66 - Clayton South, VIC 3169 - AUSTRALIA
mailto:ben(dot)stewart(at)au(dot)bosch(dot)com
http://www.bosch.com.au/