150 - Registering with a Valid Invitation

app/Invitation.php

@@ -6,11 +6,18 @@ use Illuminate\Database\Eloquent\Model;
 
 class Invitation extends Model
 {
+    protected $guarded = [];
+
     public static function findByCode($code)
     {
         return self::where('code', $code)->firstOrFail();
     }
 
+    public function user()
+    {
+        return $this->belongsTo(User::class);
+    }
+
     public function hasBeenUsed()
     {
         return $this->user_id !== null;