api/app/Admin/Forms/NewUserCoupon.php

<?php

namespace App\Admin\Forms;

use Dcat\Admin\Widgets\Form;
use Dcat\Admin\Traits\LazyWidget;
use Dcat\Admin\Contracts\LazyRenderable;

// 新人礼包配置
class NewUserCoupon extends Form implements LazyRenderable
{
    use LazyWidget;
    /**
     * Handle the form request.
     *
     * @param array $input
     *
     * @return mixed
     */
    public function handle(array $input)
    {
        //
        $obj = \App\Models\Config::where("key", "new_user_coupon")->first();
        if(!$obj) {
            $obj = new \App\Models\Config();
            $obj->key = "new_user_coupon";
        }
        $obj->val = (int)$input['coupon'];
        $obj->save();
        //
        return $this
            ->response()
            ->success('修改成功')
            ->refresh();
    }

    /**
     * Build a form here.
     */
    public function form()
    {
        //
        $this->number("coupon", "新人礼包")->required();
        //
    }

    /**
     * The data of the form.
     *
     * @return array
     */
    public function default()
    {
        //
        $obj = \App\Models\Config::where("key", "new_user_coupon")->first(); 
        if($obj) {
            return ['coupon'=>$obj->val];
        } else {
            return ['coupon' => config("avatar.new_user_coupon")];
        }
    }
}