From b66464dc46e749af194ed9db759ba68fc772a6d4 Mon Sep 17 00:00:00 2001
From: Ethan Dalool <git@voussoir.net>
Date: Sun, 20 Sep 2020 11:31:51 -0700
Subject: [PATCH] Add exceptions.DeletedObject and
 ObjectBase.assert_not_deleted.

---
 etiquette/exceptions.py | 6 ++++++
 etiquette/objects.py    | 4 ++++
 2 files changed, 10 insertions(+)

diff --git a/etiquette/exceptions.py b/etiquette/exceptions.py
index dbe28e2..4ce9034 100644
--- a/etiquette/exceptions.py
+++ b/etiquette/exceptions.py
@@ -181,6 +181,12 @@ class DatabaseOutOfDate(EtiquetteException):
     '''
     error_message = OUTOFDATE
 
+class DeletedObject(EtiquetteException):
+    '''
+    For when thing.deleted == True.
+    '''
+    error_message = '{} has already been deleted by another caller.'
+
 class FeatureDisabled(EtiquetteException):
     '''
     For when features of the system have been disabled by the configuration.
diff --git a/etiquette/objects.py b/etiquette/objects.py
index b23e050..0a2775e 100644
--- a/etiquette/objects.py
+++ b/etiquette/objects.py
@@ -68,6 +68,10 @@ class ObjectBase:
 
         return author_id
 
+    def assert_not_deleted(self):
+        if self.deleted:
+            raise exceptions.DeletedObject(self)
+
     def get_author(self):
         '''
         Return the User who created this object, or None if it is unassigned.