foreign führt zu einem Fehler

Grüß euch,

folgender Code führt zu folgendem Fehler.

Schema::create('notes', function (Blueprint $table) {
            $table->increments('id');
            $table->unsignedInteger('user_id')->index();
            $table->unsignedInteger('admin_id')->index();
            $table->text('note');
            $table->timestamps();
            $table->foreign('admin_id')->references('id')->on('users');
        });

Migrating: 2021_02_02_101233_create_notes_table

Illuminate\Database\QueryException

SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint (SQL: alter table `notes` add constraint `notes_admin_foreign` foreign key (`admin`) references `users` (`id`))

at C:\MAMP\htdocs\crm\vendor\laravel\framework\src\Illuminate\Database\Connection.php:678

674▕ // If an exception occurs when attempting to run a query, we'll format the error

675▕ // message to include the bindings with SQL, which will make this exception a

676▕ // lot more helpful to the developer instead of just the database's errors.

677▕ catch (Exception $e) {

➜ 678▕ throw new QueryException(

679▕ $query, $this->prepareBindings($bindings), $e

680▕ );

681▕ }

682▕

1 C:\MAMP\htdocs\crm\vendor\laravel\framework\src\Illuminate\Database\Connection.php:471

PDOException::("SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint")

2 C:\MAMP\htdocs\crm\vendor\laravel\framework\src\Illuminate\Database\Connection.php:471

PDOStatement::execute()

Warum? Laut Laraveldoku scheint doch alles richtig zu sein

Ich hatte zwar auf Antwort hier gehofft, das Forum scheint aber schon Ausgestorben zu sein.

Ich konnte das Problem nun selber lösen

Schema::create('notes', function (Blueprint $table) {
            $table->increments('id');
            $table->unsignedInteger('user_id')->index();
            $table->unsignedBigInteger('admin_id')->nullable();
            $table->text('note');
            $table->timestamps();
            $table->foreign('admin_id')->references('id')->on('users');
        });