Getting row values based on array of column names passed to PostgreSQL function - postgresql

Question

I'm trying to set up full text search in PostgreSQL 9.2. I created a new table to hold the content that I want to search (so that I can search across lots of different types of items), which looks like this:
CREATE TABLE search (
target_id bigint PRIMARY KEY,
target_type text,
fts tsvector
);
CREATE INDEX search_fts ON search USING gin(fts);
Every time a new item gets inserted (or updated) into one of the various tables I want to search across, it should automatically be added to the search table. Assuming that my table looks like the following:
CREATE TABLE item (id bigint PRIMARY KEY, name text NOT NULL, description text);
I created a trigger passing in the column names that I want to be able to search:
CREATE TRIGGER insert_item_search BEFORE INSERT
ON item FOR EACH ROW EXECUTE PROCEDURE
insert_search('{name, description}'::text[]);
Then created a new function insert_search as:
CREATE OR REPLACE FUNCTION insert_search(cols text[]) RETURNS TRIGGER AS $$
BEGIN
INSERT INTO search (target_id, target_type, fts) VALUES (
NEW.id, TG_TABLE_NAME, to_tsvector('english', 'foo')
);
RETURN NEW;
END;
$$ LANGUAGE PLPGSQL;
My question is, how do I pass in the table values based on cols to to_tsvector? Right now, the function is getting called and inserts the id and type correctly, but I don't know the right way to dynamically grab the other values based on the cols argument.

Answer 1

First, to pass arguments, just send them directly:
CREATE TRIGGER insert_item_search BEFORE INSERT
ON item FOR EACH ROW EXECUTE PROCEDURE
insert_search('name', 'description');
And, from PL/pgSQL you will get those arguments as an array, called TG_ARGV. But, the problem is that PL/pgSQL cannot get the values from NEW record based on their names. To do that you can either use a language that lets you do that (like PL/python or PL/perl) or use the hstore extension.
I'd stick with the last one and use hstore (unless you already use one of the other languages to create functions):
CREATE OR REPLACE FUNCTION insert_search() RETURNS TRIGGER AS $$
DECLARE
v_new hstore;
BEGIN
v_new = hstore(NEW); -- convert the record to hstore
FOR i IN 0..(TG_NARGS-1) LOOP
INSERT INTO search (target_id, target_type, fts) VALUES (
NEW.id, TG_TABLE_NAME, to_tsvector('english', v_new -> TG_ARGV[i])
);
END LOOP;
RETURN NEW;
END;
$$ LANGUAGE PLPGSQL;
As you can see above, I used the hstore's operator -> to get the value based on the name (on TG_ARGV[i]).

Answer 2

You can access the parameters specified in the trigger definition with the TG_ARGV variable. You can find documentation on that here. TG_ARGV is an array accessed by a 0 based index. So it would be something like TG_ARGV[0], TG_ARGV[1], and so on.