Self-heal statistics results model

Happens when multiple results are created using the
same slug value. Forum topic 1404.

Signed-off-by: Roberto Rosario <roberto.rosario@mayan-edms.com>

HISTORY.rst

@@ -9,6 +9,9 @@
   generalized utility of the storages app.
 - Add book link to the documentation.
 - Make the statistics slug field unique.
+- Self-heal statistics results model when multiple
+  results are created using the same slug value.
+  Forum topic 1404.
 
 3.2.10 (2019-11-19)
 ===================

mayan/apps/mayan_statistics/classes.py

@@ -158,6 +158,11 @@ class Statistic(object):
             return StatisticResult.objects.get(slug=self.slug)
         except StatisticResult.DoesNotExist:
             return StatisticResult.objects.none()
+        except StatisticResult.MultipleObjectsReturned:
+            # This should not happen. Self-heal by deleting the duplicate
+            # results.
+            StatisticResult.objects.filter(slug=self.slug).delete()
+            return StatisticResult.objects.none()
 
     def get_results_data(self):
         results = self.get_results()