PSQL Database Update trigger update procedure works. But insert procedure doesn't - ruby-on-rails

Question

I’m currently trying to implement Postgres text search for my rails app. My migrations run successfully creating all the tables. One of my migrations adds a trigger to update a ts_vector column (TSV) on my listings table. It does a bunch of joins on tables and two joins on intermediate tables. Not sure if this trigger is the most efficient but it works when it’s called by a procedure.
CREATE OR REPLACE FUNCTION update_listings_tsv() RETURNS trigger AS $$
BEGIN
NEW.tsv := (
SELECT
setweight(to_tsvector(l.item_name), 'A') ||
setweight(to_tsvector(l.description), 'B') ||
setweight(to_tsvector(categories.name), 'B') ||
setweight(to_tsvector(sub_categories.name), 'B') ||
setweight(to_tsvector(sizes.name), 'B') ||
setweight(to_tsvector(users.username), 'C') ||
setweight(to_tsvector(string_agg(DISTINCT brands.name, ',')), 'A') ||
setweight(to_tsvector(string_agg(DISTINCT colours.name, ',')), 'B')
FROM listings l
JOIN users ON users.id = l.user_id
JOIN categories ON categories.id = l.category_id
JOIN sub_categories ON sub_categories.id = l.sub_category_id
JOIN sizes ON sizes.id = l.size_id
JOIN conditions ON conditions.id = l.condition_id
JOIN brands_listings ON brands_listings.listing_id = l.id
JOIN brands ON brands.id = brands_listings.brand_id
JOIN colours_listings ON colours_listings.listing_id = l.id
JOIN colours ON colours.id = colours_listings.colour_id
WHERE l.id = NEW.id
GROUP BY l.id, users.id, categories.id, sub_categories.id, sizes.id, conditions.id
);
RETURN NEW;
END;
$$ LANGUAGE plpgsql;
This is where the problem is:
The update procedure that calls the trigger works fine. As intended when a listing column updates the TSV column for that exact listing also updates.
CREATE TRIGGER tsvectorupdateupdate BEFORE UPDATE
ON listings FOR EACH ROW EXECUTE PROCEDURE update_listings_tsv();
The insert procedure doesn’t work. I’ve tried it with a BEFORE and AFTER INSERT. I don’t know where the problem is. After a db:reset the TSV column should already be populated with a ts_vector value.
CREATE TRIGGER tsvectorupdateinsert AFTER INSERT OR UPDATE
ON listings FOR EACH ROW EXECUTE PROCEDURE update_listings_tsv(tsv);

Answer 1

If you do an AFTER trigger, it is too late to change the value. If you do a BEFORE trigger, it is too early to join against the (not yet existing) row in the table "listings". You need to get the new data from NEW, not from "listings".
I've reduced this to its minimal essence, fleshing it back out with extra tables and columns is up to you:
CREATE OR REPLACE FUNCTION update_listings_tsv() RETURNS trigger AS $$
BEGIN
NEW.tsv := (
SELECT
setweight(to_tsvector(NEW.item_name), 'A') ||
setweight(to_tsvector(users.username), 'C')
FROM users where users.id = NEW.user_id
);
RETURN NEW;
END;
$$ LANGUAGE plpgsql;
CREATE TRIGGER tsvectorupdateinsert BEFORE INSERT OR UPDATE
ON listings FOR EACH ROW EXECUTE PROCEDURE update_listings_tsv();