Laravel 5-如何通过Query Builder或Eloquent在两个以上的表/查询中使用联合？

$users = DB::table('users')
            ->join('orders', 'users.id', '=', 'orders.user_id')
            ->join('products', 'orders.product_id', '=', 'products.id')
            ->select('users.*', 'orders.order_number', 'products.name')
            ->get();

class User extends Model
{
    public function orders()
    {
        return $this->hasMany(Order::class);
    }
}

class Order extends Model
{
    public function user()
    {
        return $this->belongsTo(User::class);
    }

    public function product()
    {
        return $this->belongsTo(Product::class);
    }
}

class Product extends Model
{
    public function orders()
    {
        return $this->hasMany(Order::class);
    }
}

$users = User::with('orders.product')->get();