fix occasional bug

core/models.py

@@ -1261,7 +1261,12 @@ class Work(models.Model):
             self.save()
             return self.selected_edition 
         except IndexError:
-            #should only happen if there are no editions for the work
+            #should only happen if there are no editions for the work, 
+            #which can happen when works are being merged
+            try:
+                return WasWork.objects.get(was=self.id).work.preferred_edition
+            except WasWork.DoesNotExist:
+                #should not happen
                 return None
         
     def last_campaign_status(self):

core/tests.py

@@ -789,6 +789,20 @@ class SafeGetWorkTest(TestCase):
         self.assertEqual(work, w1)
         self.assertRaises(Http404, safe_get_work, 3)
 
+class WorkTests(TestCase):    
+    def test_preferred_edition(self):
+        w1 = models.Work.objects.create()
+        w2 = models.Work.objects.create()
+        ww = models.WasWork.objects.create(work=w1, was= w2.id)
+        e1 = models.Edition.objects.create(work=w1)
+        self.assertEqual(e1, w1.preferred_edition)
+        e2 = models.Edition.objects.create(work=w1)
+        w1.selected_edition=e2
+        w1.save()
+        self.assertEqual(e2, w1.preferred_edition)
+        self.assertEqual(e2, w2.preferred_edition)
+
+        
 class DownloadPageTest(TestCase):
     def test_download_page(self):
         w = models.Work()