1.首先先設定user level ,定義user level 2 為VIP,

為order_items添加新的欄位,當他是VIP時享受優惠價格,故創建migration

php artisan make:migration add_discount_to_order_items

2.增加price欄位及user層級(default值為1),接著執行migrate

public function up()
    {
        Schema::table('order_items', function (Blueprint $table) {
            $table->integer('price')->after('order_id');
        });

        Schema::table('users', function (Blueprint $table) {
            $table->integer('level')->default(1)->after('id');
        });

    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::table('order_items', function (Blueprint $table) {
            $table->dropColumn('price');      
        });
        Schema::table('users', function (Blueprint $table) {
            $table->dropColumn('level');      
        });
    }

3.接著來到Cart Model修正

首先先定義一個private(私有變數) = $rate 1

額外理解關於PHP OOP

PHP-物件導向(OOP)介紹

private $rate = 1;

4.接著設計當user 等級來到 level 2 的時候其rate =0.8 所以在foreach前面定義一個 if 條件式

if($this->user->level == 2){
            $this->rate = 0.8;
        }

5.最後修改orderItem()函數 欄位price = price * rate

foreach($this->cartItems as $cartItem){
            $order->orderItems()->create([
                'product_id' => $cartItem->product_id,
                'price' => $cartItem->product->price * $this->rate
            ]);

6.全部程式碼為

7.接著進行測試,首先將User等級改為Level 2 執行POSTMAN結帳功能

8.結帳後可以看到OrderItem價格改變