    /**
     * {@inheritdoc}
     */
    public function safeUp()
    {
        $this->addColumn('startups','created_at', $this->string()->null());
        $this->addColumn('startups','updated_at',$this->string()->null());
        $this->addColumn('comments','startup_id',$this->integer()->notNull());
        $this->addForeignKey(
            'fk-startup-id',
            'comments',
            'startup_id',
            'startups',