laravel 搜索之when()函数

#前端代码
<form action="{{route('admin.role.index')}}" method="get" class="layui-form layui-col-space5">
    <div class="layui-inline layui-show-xs-block">
        <input class="layui-input"  autocomplete="off" placeholder="输入想要搜索的角色名称" name="kw" id="kw">
    </div>
    <div class="layui-inline layui-show-xs-block">
        <button class="layui-btn"  lay-submit="" lay-filter="sreach">
             <i class="layui-icon">&#xe615;</i>
        </button>
    </div>
</form>
#后端代码
public function index(Request $request)
    {
        $kw = $request->get('kw');
        //参数一：变量值存在，执行回调；否则不执行回调
        $data = Role::when($kw, function ($query) use ($kw) {

            $query->where('name', 'like', "%{$kw}%");

        })->paginate($this->pageNum);

        return view('admin.role.index', compact('data'));
    }