Trigger after insert, update a related model Postgresql - postgresql

Question

This is the first time I'm creating a trigger, so I've got a little bit confused. I'm following this guide.
Here is what I've done so far:
DROP TRIGGER IF EXISTS "update_metas" ON "post";
CREATE TRIGGER "update_metas"
AFTER INSERT ON "post"
FOR EACH ROW EXECUTE PROCEDURE update_post_count();
I have two tables: user and post. What I need to do is to increment the column user.postCount for each new post created. The foreign key is post.user_id
The procedure I'm creating is the following:
CREATE FUNCTION update_post_count() RETURNS TRIGGER AS $updates_user_postCount$
BEGIN
-- I know that NEW contains the new post info, so I
-- can gather the user_id by doing NEW.post_id.
--
-- What exactly should I do here?
RETURN NEW;
END;
$updates_user_postCount$ LANGUAGE plpgsql;
How should I structure this procedure? Can I just use a direct SQL query, something like:
UPDATE "user"
SET "user"."post_count" = "user"."post_count" + 1
WHERE "user"."_id" = NEW.idol_id;
UPDATE
I've tried using that SQL statement inside the procedure, but it returns the error error: column "user" of relation "user" does not exist.
Here is the SQL statement that I used to create both user and post tables:
CREATE TABLE IF NOT EXISTS "user" (
_id BIGSERIAL UNIQUE,
__id TEXT UNIQUE,
fbid VARCHAR(100),
name VARCHAR(100) NOT NULL,
email VARCHAR(100) NOT NULL UNIQUE,
password VARCHAR(512) NOT NULL,
profile_picture VARCHAR(512),
profile_cover VARCHAR(512),
profile_about TEXT,
profile_birth_date BIGINT,
social_facebook VARCHAR(256),
social_twitter VARCHAR(256),
social_instagram VARCHAR(256),
post_count BIGINT,
highlighted BOOLEAN,
idol BOOLEAN,
free BOOLEAN,
blocked BOOLEAN
);
CREATE TABLE IF NOT EXISTS "post" (
_id BIGSERIAL UNIQUE,
__id TEXT UNIQUE,
idol_id BIGINT,
removed BOOLEAN,
free BOOLEAN,
created_at BIGINT,
hashtags VARCHAR(1024),
audio_src VARCHAR(512),
audio_size INTEGER,
audio_length INTEGER,
FOREIGN KEY ("idol_id") REFERENCES "user"("_id")
);

Answer 1

Your trigger function is largely correct. The only problem is that an UPDATE statement cannot use the table.column notation.
From the documentation: Do not include the table's name in the specification of a target column — for example, UPDATE tab SET tab.col = 1 is invalid.
CREATE FUNCTION update_post_count() RETURNS TRIGGER AS $updates_user_postCount$
BEGIN
UPDATE "user"
SET "post_count" = "post_count" + 1
WHERE "_id" = NEW.idol_id;
RETURN NEW;
END;
$updates_user_postCount$ LANGUAGE plpgsql;