Exception handling in PostgreSQL function with Django - django

Question

have write the following store procedure in Postgres. This SP simply accept the incoming parameters, insert it into the table and return current identity. More I have also declare an addition variable that will tell is the sp runs successfully or not.
I am new to Postgres and have not much knowledge about Postgres way to do this. I want some thing like BEGIN TRY, END TRY and BEGIN CATCH, END CATCH like we do in MSSQL.
CREATE OR REPLACE FUNCTION usp_save_message(msg_sub character varying(80), msg_content text, msg_type character(12), msg_category character(255),msg_created_by character(255),msg_updated_by character(255))
RETURNS msg_id character, success boolean AS
$BODY$
DECLARE
msg_id character;
success boolean;
BEGIN
BEGIN TRY:
set success = 0
set msg_id = INSERT INTO tbl_messages(
message_subject, message_content, message_type, message_category,
created_on, created_by, updated_on, updated_by)
VALUES (msg_sub, msg_cont, msg_type,msg_category, LOCALTIMESTAMP,
msg_created_by, LOCALTIMESTAMP, msg_updated_by) RETURNING message_id;
set success = 1
RETURN msg_id,success;
END;
$BODY$
LANGUAGE plpgsql VOLATILE
I want something like this:
begin proc()
BEGIN
BEGIN TRY:
set success = 0
execute the query
set success = 1
END TRY
BEGIN CATCH:
set success = 0
END CATCH
set success = 1
END
More I have to catched both these return values in django views.
I have updated the question and it is as now;
Here is the table,
CREATE TABLE tbl_messages
(
message_subject character varying(80),
message_content text,
message_type character(12),
message_category character(255),
created_on timestamp without time zone,
created_by character(255),
updated_on timestamp without time zone,
updated_by character(255),
message_id serial NOT NULL,
CONSTRAINT tbl_messages_pkey PRIMARY KEY (message_id)
)
WITH (
OIDS=FALSE
);
ALTER TABLE tbl_messages
OWNER TO gljsxdlvpgfvui;
Here is the function i created;
CREATE FUNCTION fn_save_message(IN msg_sub character varying, IN msg_cont text, IN msg_type character varying, IN msg_category character varying, IN msg_created_by character varying, IN msg_updated_by character varying, OUT success boolean, OUT msg_id integer) RETURNS integer AS
$BODY$BEGIN
BEGIN
INSERT INTO tbl_messages
(message_subject, message_content, message_type, message_category,
created_on, created_by, updated_on, updated_by)
VALUES
(msg_sub, msg_cont, msg_type, msg_category, LOCALTIMESTAMP,
msg_created_by, LOCALTIMESTAMP, msg_updated_by)
returning message_id
into msg_id;
success := true;
EXCEPTION
WHEN others then
success := false;
msg_id := null;
END;
return msg_id,success;
END;$BODY$
LANGUAGE plpgsql VOLATILE NOT LEAKPROOF
COST 100;
ALTER FUNCTION public.fn_save_message(IN character varying, IN text, IN character varying, IN character varying, IN character varying, IN character varying)
OWNER TO gljsxdlvpgfvui;
But it is not still working... i don't know what id have done wrong now, any django/postgres expert here kindly help me out.

Answer 1

There are several problems with your function:
Statements need to be terminated with a ; - always
Variable assignments are done using := (see: http://www.postgresql.org/docs/current/static/plpgsql-statements.html#PLPGSQL-STATEMENTS-ASSIGNMENT)
You can't return more than one value from a function (unless you create a set returning function, return an object or use out parameters)
Boolean values are true or false. Not 0 or 1 (those are numbers)
The result of an automatically generated ID value is better obtained using lastval() or `` INSERT ... RETURNING expressions INTO ...not through aSET` statement.
Exception handling is done using the exception clause as documented in the manual
So you need something like this:
DECLARE
....
BEGIN
BEGIN
INSERT INTO tbl_messages
(message_subject, message_content, message_type, message_category,
created_on, created_by, updated_on, updated_by)
VALUES
(msg_sub, msg_cont, msg_type,msg_category, LOCALTIMESTAMP,
msg_created_by, LOCALTIMESTAMP, msg_updated_by)
returning message_id
into msg_id;
success := true;
EXCEPTION
WHEN others then
success := false;
msg_id := null;
END;
return msg_id;
END;
But as I said: you can't return more than one value from a function. The only way to do this is to declare OUT parameters, but personally I find them a bit hard to handle in SQL clients.
You have the following options to report an error to the caller:
let the caller handle the exception/error that might arise (which is what I prefer)
define a new user defined data type that contains the message_id and the success flag and return that (but that means you lose the error message!)
return a NULL for the message_id to indicate that something went wrong (but that also means you lose the error information)
Use out parameters to pass both values. An example is available in the manual: http://www.postgresql.org/docs/current/static/xfunc-sql.html#XFUNC-OUTPUT-PARAMETERS

Answer 2

CREATE FUNCTION fn_save_message3(IN msg_sub character varying, IN msg_cont text, IN msg_type character varying, IN msg_category character varying, IN msg_created_by character varying, IN msg_updated_by character varying) RETURNS integer AS
$BODY$ DECLARE msg_id integer := 0;
BEGIN
INSERT INTO tbl_messages
(message_subject, message_content, message_type, message_category,
created_on, created_by, updated_on, updated_by)
VALUES
(msg_sub, msg_cont, msg_type, msg_category, LOCALTIMESTAMP,
msg_created_by, LOCALTIMESTAMP, msg_updated_by);
Select into msg_id currval('tbl_messages_message_id_seq');
return msg_id;
END;$BODY$
LANGUAGE plpgsql VOLATILE NOT LEAKPROOF
COST 100;
ALTER FUNCTION public.fn_save_message(IN character varying, IN text, IN character varying, IN character varying, IN character varying, IN character varying)
OWNER TO gljsxdlvpgfvui;
SELECT fn_save_message3('Test','fjaksdjflksadjflas','email','news','taqi#gmail.com','');