public static function delete($topic_id)
    {
        // Delete the topic and any redirect topics
        $where_delete_topic = [
            ['id' => $topic_id],
            ['moved_to' => $topic_id]
        ];

        DB::forTable('topics')
            ->where_any_is($where_delete_topic)
            ->delete_many();

        // Delete posts in topic
        DB::forTable('posts')
            ->where('topic_id', $topic_id)
            ->delete_many();

        // Delete any subscriptions for this topic
        DB::forTable('topic_subscriptions')
            ->where('topic_id', $topic_id)
            ->delete_many();
    }