.js

var qb = knex.select('songs.id', 'songs.name AS song', 'artists.name AS artist', 'songs.path', 'albums.name AS album')
  .from('songs')
  .join('genreAssociation', 'songs.id', 'genreAssociation.id_songs')
  .join('artists', 'songs.id_artists', 'artists.id')
  .join('albums', 'songs.id_albums', 'albums.id')
  .where('genreAssociation.id', req.params.id)

if (req.session.playedSongs && req.session.playedSongs.length != 0 && req.session.playedSongs != []) {
  qb.whereNotIn('songs.id', req.session.playedSongs);
}