如何在Laravel中仅订购一次产品

Question

用户对订单的出价不能超过一次。如果用户再次单击该订单，则应该在响应页面上提示他，提示用户先前已经对该订单进行了出价。

OrderController.php

public function store(Request $request)
{
    $this->validate(request(), [
        'category_id' => 'required'
    ]);

    $order = Order::findOrFail(request('category_id'));

    if (auth()->user()->checkOrder($order)) {
        alert()->error('Warning', 'You ordered already');

        return redirect()->back();
    }
}

User.php

public function checkOrder($category)
{
    return !! Order::where('user_id' , $this->id)->where('category_id' , $category->id)->first();
}