Problem with PLPGSQL function return, uuid involved - postgresql

Question

I want to assign serial numbers from a sequence, along with uuids that are generated automatically. My table looks like
CREATE TABLE master_serialnumbers
(
uuident uuid PRIMARY KEY DEFAULT uuid_generate_v1(),
serno integer GENERATED ALWAYS AS IDENTITY UNIQUE,
requester varchar(20) NOT NULL
);
I can now generate a serial number with
INSERT INTO master_serialnumbers(requester) VALUES ('XY')
RETURNING (uuident,serno,requester);
To automate this and generate a block of several serial numbers, I can use a function like this:
CREATE FUNCTION gen_serials_A(num_serials integer, req varchar(20))
RETURNS SETOF master_serialnumbers
AS $$
DECLARE
new_id uuid;
rr master_serialnumbers%ROWTYPE; -- or simply RECORD
tmpSQL TEXT;
BEGIN
RAISE NOTICE 'generate % serial numbers', num_serials;
CREATE TEMPORARY TABLE tmpIds (id uuid NOT NULL PRIMARY KEY);
FOR i IN 1..num_serials LOOP
RAISE NOTICE 'serno %', i;
INSERT INTO master_serialnumbers(space, requester) VALUES (spc, req)
RETURNING (uuident) INTO new_id;
INSERT INTO tmpIds(id) VALUES (new_id);
END LOOP;
FOR rr IN EXECUTE 'SELECT * FROM master_serialnumbers
WHERE uuident IN (SELECT id FROM tmpIds)' LOOP
RETURN NEXT rr;
END LOOP;
tmpSQL := 'DROP TABLE tmpIds';
EXECUTE tmpSQL;
RETURN;
END
$$ LANGUAGE plpgsql;
This does work, but it seems cumbersome to store the values in a temporary table and have two loops. So I tried to shorten it like this:
CREATE FUNCTION gen_serials(num_serials integer, req varchar(20))
RETURNS SETOF master_serialnumbers
AS $$
DECLARE
rr master_serialnumbers%ROWTYPE;
BEGIN
RAISE NOTICE 'generate % serial numbers', num_serials;
FOR i IN 1..num_serials LOOP
RAISE NOTICE 'serno %', i;
INSERT INTO master_serialnumbers(requester) VALUES (req)
RETURNING (uuident,serno,requester) INTO rr;
RAISE NOTICE 'rr is %', rr;
RETURN NEXT rr;
END LOOP;
RETURN;
END
$$ LANGUAGE plpgsql;
– but the INSERT throws an error
invalid input syntax for type uuid: »(12345678-1234-1234-1234-123456789abc,1,A)«
Changing the declaration to rr RECORD now passes the INSERT:
rr is ("(12345678-1234-1234-1234-123456789abc,1,A)")
ERROR: wrong record type supplied in RETURN NEXT
DETAIL: Returned type does not match expected type uuid in column 1.
Apparently all has been converted into a string.
And changing the return type also to SETOF RECORD yields another error:
ERROR: function with set result called in a context that cannot process set results
(German error messages translated back to English by me, sorry for that).
Any ideas what's (not) happening here? Perhaps I am doing it much too long-winded at all by using a function with procedural loops?

Answer 1

To automate this and generate a block of several serial numbers, I can use a function
Don't make it so complicated. Use something like
INSERT INTO master_serialnumbers(requester)
VALUES ('XY', 'YZ', 'ZA')
RETURNING uuident, serno, requester;
or
INSERT INTO master_serialnumbers(requester)
SELECT UNNEST(ARRAY['XY', 'YZ', 'ZA']) -- useful for parameterised queries
RETURNING uuident, serno, requester;
or
INSERT INTO master_serialnumbers(requester)
SELECT 'XY'
FROM generate_series(1, 20) -- useful for arbitrary repetition of the same value
RETURNING uuident, serno, requester;
(a set-returning function to create a series of numbers)