我正在嘗試將數據寫入我的 SQLite 數據庫。我認為我的遷移文件和外鍵存在錯誤。我試圖更改文件的名稱，使外鍵可以為空并清除 Laravel 的緩存。您是否熟悉錯誤處理程序顯示的錯誤，或者您能否將我指向一個可以幫助我理解我做錯了什么的頁面？非常感謝您提前。遷移文件：<?phpuse Illuminate\Support\Facades\Schema;use Illuminate\Database\Schema\Blueprint;use Illuminate\Database\Migrations\Migration;class CreateSqrTable extends Migration{    /**     * Run the migrations.     *     * @return void     */    public function up()    {        Schema::create('sqrs', function (Blueprint $table) {            $table->bigIncrements('id');            $table->unsignedInteger('user_id')->nullable();             $table->string('qr_link');            $table->timestamps();            $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');         });    }    /**     * Reverse the migrations.     *     * @return void     */    public function down()    {        Schema::dropIfExists('sqr');    }}模型文件：<?phpnamespace App;use Illuminate\Database\Eloquent\Model;// sQR stands for Saved QR-Codeclass sqr extends Model{    protected $fillable = [        'qr_link', 'user_id'    ];}保存的控制器：<?phpnamespace App\Http\Controllers;use Illuminate\Http\Request;use App\sqr;class saveController extends Controller{    public function save(Request $request)    {        $sqr = new sqr;        $sqr->qr_link =     $request->qr_link;        $sqr->user_id =     1;        $sqr->save();        return redirect('/');    }}前端刀片文件：<form method="post" action="/save">        @csrf       <input type="hidden" name="qr_link" value="{{ session('url') }}">       <button class="btn btn-success">Save this QR</button>    </form>我得到的錯誤如下：SQLSTATE[23000]: Integrity constraint violation: 19 FOREIGN KEY constraint failed (SQL: insert into "sqrs" ("qr_link", "user_id", "updated_at", "created_at") values (images/1567444499.svg, 1, 2019-09-02 17:37:23, 2019-09-02 17:37:23))