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.courseareasIN 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
SELECTtransid 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.stewart@au.bosch.com
http://www.bosch.com.au/
