Refs #678 -- Allow deletion of events that do not have any orders

src/pretix/base/models/event.py

@@ -544,6 +544,9 @@ class Event(EventMixin, LoggedModel):
             Q(is_superuser=True) | Q(twp=True)
         )
 
+    def allow_delete(self):
+        return not self.orders.exists() and not self.invoices.exists()
+
 
 class SubEvent(EventMixin, LoggedModel):
     """

src/pretix/base/models/log.py

@@ -41,7 +41,7 @@ class LogEntry(models.Model):
     datetime = models.DateTimeField(auto_now_add=True, db_index=True)
     user = models.ForeignKey('User', null=True, blank=True, on_delete=models.PROTECT)
     api_token = models.ForeignKey('TeamAPIToken', null=True, blank=True, on_delete=models.PROTECT)
-    event = models.ForeignKey('Event', null=True, blank=True, on_delete=models.CASCADE)
+    event = models.ForeignKey('Event', null=True, blank=True, on_delete=models.SET_NULL)
     action_type = models.CharField(max_length=255)
     data = models.TextField(default='{}')
     visible = models.BooleanField(default=True)