public function add($priceId)
{
$cart = \App\Cart::whereUserIdAndPriceId($this->user()->id, $priceId)->first();
if (is_null($cart)) {
$cart = new \App\Cart();
$cart->price_id = $priceId;
$cart->user_id = $this->user()->id;
$cart->quantity = 1;
} else {
$cart->quantity = $cart->quantity + 1;
}
$cart->save();
return redirect()->back();
}