Support oft parent groups

app/Models/Tenant.php

@@ -4,6 +4,7 @@ namespace App\Models;
 
 use App\Scopes\CommonModel;
 use App\Support\Text;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
 
 /**
  * @property string $slug
@@ -35,6 +36,7 @@ use App\Support\Text;
  * @property string|null $tax_exemption_reason
  * @property string|null $tax_exemption_note
  * @property string $vat_pricing_mode
+ * @property int $parent_group_id
  */
 class Tenant extends CommonModel
 {
@@ -46,9 +48,15 @@ class Tenant extends CommonModel
     {
         static::creating(static function (self $tenant): void {
             $tenant->invoice_prefix ??= strtoupper((string) $tenant->slug);
+            // Die Parent Group ist Pflicht; ohne Angabe landet der Mandant bei „Ohne Zuordnung".
+            $tenant->parent_group_id ??= ParentGroup::fallback()->id;
         });
     }
 
+    public function parentGroup() : BelongsTo {
+        return $this->belongsTo(ParentGroup::class, 'parent_group_id');
+    }
+
     public static function getTempDirectory() : string {
         return currentTenant()->slug . '/temp-data/';
     }
@@ -95,6 +103,7 @@ class Tenant extends CommonModel
         'tax_number',
         'vat_id',
         'invoice_prefix',
+        'parent_group_id',
     ];
 
     protected $casts = [