guarded instead of fillable

app/Models/City.php

@@ -4,31 +4,40 @@ namespace App\Models;
 
 use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Model;
+use Spatie\Sluggable\HasSlug;
+use Spatie\Sluggable\SlugOptions;
 
 class City extends Model
 {
     use HasFactory;
+    use HasSlug;
 
     /**
-     * The attributes that are mass assignable.
-     *
+     * The attributes that aren't mass assignable.
      * @var array
      */
-    protected $fillable = [
-        'country_id',
-        'name',
-    ];
+    protected $guarded = [];
 
     /**
      * The attributes that should be cast to native types.
-     *
      * @var array
      */
     protected $casts = [
-        'id' => 'integer',
+        'id'         => 'integer',
         'country_id' => 'integer',
     ];
 
+    /**
+     * Get the options for generating the slug.
+     */
+    public function getSlugOptions(): SlugOptions
+    {
+        return SlugOptions::create()
+                          ->generateSlugsFrom('name')
+                          ->saveSlugsTo('slug')
+                          ->usingLanguage('de');
+    }
+
     public function country(): \Illuminate\Database\Eloquent\Relations\BelongsTo
     {
         return $this->belongsTo(Country::class);