Re: Problem while using start transaction ans commit;

Sri,

> I have a small problem in using nested transactions while
> working on Postgres 8.0.

This is a known problem with Postgres 8.0 - there is no support for
nested transactions (which occurs when calling functions). Your best bet
would be to raise an exception within B or C - this will cause a
rollback to wherever the exception is caught. If you surround the calls
to B and C in a block to catch the exception, this will provide
transaction-like semantics.

An example:

----------
CREATE OR REPLACE FUNCTION tr_addcourse(employeeno, int4, coursename,
float4, text, timestamptz, int4)
RETURNS int4 AS
$BODY$-- Use case: 10.2.9: Add a course

DECLARE
transid int4;
cid 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

-- Start the transaction, lock tables
LOCK TABLE backend.courses IN ACCESS EXCLUSIVE MODE;
LOCK TABLE backend.courseareas IN SHARE 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 for a duplicate course name.
IF tt_course_name_active(cname) THEN
SELECT -2000 INTO errcode; -- E_DUP_COURSE
RAISE EXCEPTION 'Course "%" already exists.', cname;
END IF;

-- Check for course area status
SELECT tt_coursearea_status(carea) INTO errcode;
IF NOT errcode = 0 THEN -- NOT errcode = SUCCESS
RAISE EXCEPTION 'Error finding active course area %', carea;
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;

-- Get the next course ID
SELECT nextval('backend.courses_courseid_seq') INTO cid;

-- Insert the row
INSERT INTO backend.courses
(transactionid, courseid, coursearea, coursename, active, duration,
description, contentdate, valid_months)
VALUES (transid, cid, carea, cname, TRUE, dur, desc, cdate,
valid_mths);

-- Success
RETURN cid;

EXCEPTION
WHEN RAISE_EXCEPTION THEN
RETURN errcode;

WHEN OTHERS THEN
RETURN -32767; -- E_UNKNOWN

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

----------

In this code, whenever an exception is raised, the system will rollback
to the start of the block (BEGIN).

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/