Flarum\Core\Repository\DiscussionRepository::getReadIds PHP Method

    public function getReadIds(User $user)
    {
        return Discussion::leftJoin('users_discussions', 'users_discussions.discussion_id', '=', 'discussions.id')->where('user_id', $user->id)->where('read_number', '>=', new Expression('last_post_number'))->lists('id')->all();
    }

 /**
  * {@inheritdoc}
  */
 protected function conditions(AbstractSearch $search, array $matches, $negate)
 {
     if (!$search instanceof DiscussionSearch) {
         throw new LogicException('This gambit can only be applied on a DiscussionSearch');
     }
     $actor = $search->getActor();
     if ($actor->exists) {
         $readIds = $this->discussions->getReadIds($actor);
         $search->getQuery()->where(function ($query) use($readIds, $negate, $actor) {
             if (!$negate) {
                 $query->whereNotIn('id', $readIds)->where('last_time', '>', $actor->read_time ?: 0);
             } else {
                 $query->whereIn('id', $readIds)->orWhere('last_time', '<=', $actor->read_time ?: 0);
             }
         });
     }
 }