Albert Vernon Smith presumably uttered the following on 01/03/06 13:36:
I figured it out myself. Not TOO difficult. I was just having a hard
time wading through the documentation before. Giving the answer out
here, just in case any one else wants to see the solution (not using
reserved words ;-)).
1. Made function:
CREATE FUNCTION "return_one_id" () RETURNS "trigger" AS '
DECLARE
my_id bigint;
BEGIN
select into my_id one_id from one where one_text=NEW.one_text;
NEW.one_id := my_id;
return NEW;
END;
' LANGUAGE "plpgsql"
2. Made trigger:
CREATE TRIGGER return_one_id BEFORE INSERT OR UPDATE ON two FOR EACH
ROW EXECUTE PROCEDURE return_one_id()
Voila!
-albert
On 3.1.2006, at 14:36, Albert Vernon Smith wrote:
I have two tables, listed as below. I'm inserting values for "text"
into table "two" (which must already exist as "text" values in table
"one"). When I do that, I'd like to also insert the associated
"one_id" value from table "one" into the field "two.one_id". How is
best to go about that? I imagine this would be best be done with a
trigger rather than a rule, but I don't know enough on how to go
about that. Can someone help point me in the right direction. (I
did try it with rules as listed below, but the serial value
increments, so the approach doesn't work on a single row.)
--
My tables:
CREATE TABLE "one" (
"one_id" BIGSERIAL,
"text" text NOT NULL,
CONSTRAINT "iu_text" UNIQUE (text)
)
CREATE TABLE "two" (
"two_id" BIGSERIAL,
"text" text NOT NULL,
"one_id" bigint,
CONSTRAINT "$1" FOREIGN KEY (text) REFERENCES one(text) ON UPDATE
SET NULL
)
--
My failed rule approaches:
CREATE RULE two_insert AS ON INSERT TO two DO UPDATE two SET one_id =
(SELECT one.one_id FROM one WHERE (new.text = one.text)) WHERE
(new.two_id = two.two_id);
The following does work, but it updates all rows with the same text.
I'd rather be more efficient, and only work with the current row.:
CREATE RULE two_insert AS ON INSERT TO two DO UPDATE two SET one_id =
(SELECT one.one_id FROM one WHERE (new.text = one.text)) WHERE
(new.text = two.text);
The reason the rule failed, by the way is that the rule gets expanded
(like a macro). Whereas in a function "new.two_id" actually uses the
value of two_id that is about to be inserted into the table, in a rule
situation "new.two_id" gets expanded into its definition, namely
nextval(sequence name) so the comparison is between a two_id that really
doesn't exist in the table (its value is created by the rule after the
two_id that gets created on insert) which will always result in a non-match.
I had this same issue with a pair of table I had where I wanted to
update a customer information table with a live customer number that was
created in a different table. As in your case, a trigger solved my
situation.
Sven
