Refs #131 -- Allow to regenerate an invoice

src/pretix/base/models/invoices.py

@@ -5,6 +5,7 @@ from decimal import Decimal
 
 from django.db import DatabaseError, models
 from django.db.models import Max
+from django.utils.functional import cached_property
 
 
 def invoice_filename(instance, filename: str) -> str:
@@ -80,6 +81,10 @@ class Invoice(models.Model):
         """
         return '%s-%05d' % (self.event.slug.upper(), self.invoice_no)
 
+    @cached_property
+    def canceled(self):
+        return self.refered.filter(is_cancellation=True).exists()
+
     class Meta:
         unique_together = ('event', 'invoice_no')