jam-cloud/db/up/user_online.sql

-- this was patched on the server without a proper migration, so the migration script here takes care to make sure it can run 2x
ALTER TABLE users DROP COLUMN IF EXISTS online;
DROP TRIGGER IF EXISTS connection_up_down ON connections;

ALTER TABLE users ADD COLUMN online BOOL DEFAULT FALSE NOT NULL;

CREATE OR REPLACE FUNCTION manage_user_online() RETURNS TRIGGER
STRICT VOLATILE AS $$
  BEGIN
    IF (TG_OP = 'DELETE') THEN
      UPDATE users set ONLINE = (SELECT COUNT(conn.id) FROM connections conn WHERE conn.user_id = OLD.user_id) > 0 WHERE users.id = OLD.user_id;
      RETURN NULL;
    ELSIF (TG_OP = 'INSERT') THEN
      UPDATE users set ONLINE = (SELECT COUNT(conn.id) FROM connections conn WHERE conn.user_id = NEW.user_id) > 0 WHERE users.id = NEW.user_id;
      RETURN NULL;
    END IF;
    RETURN NULL;
  END;
$$ LANGUAGE plpgsql;


DELETE FROM connections;

CREATE TRIGGER connection_up_down AFTER INSERT OR DELETE
ON connections FOR EACH ROW EXECUTE PROCEDURE manage_user_online(user_id);

-- ONE time bootstrap the new online field
-- UPDATE users set online = (SELECT COUNT(conn.id) FROM connections conn WHERE conn.user_id = users.id) > 0;