Update statistics migration to rename duplicates

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

HISTORY.rst

@@ -12,6 +12,8 @@
 - Self-heal statistics results model when multiple
   results are created using the same slug value.
   Forum topic 1404.
+- Update mayan_statistics migration 0002 to rename
+  duplicate slugs.
 
 3.2.10 (2019-11-19)
 ===================

mayan/apps/mayan_statistics/migrations/0002_auto_20191116_0236.py

@@ -1,10 +1,30 @@
-# -*- coding: utf-8 -*-
-# Generated by Django 1.11.25 on 2019-11-16 02:36
 from __future__ import unicode_literals
 
 from django.db import migrations, models
 
 
+def operation_rename_duplicates(apps, schema_editor):
+    StatisticResult = apps.get_model(
+        app_label='mayan_statistics', model_name='StatisticResult'
+    )
+    slugs = []
+
+    for entry in StatisticResult.objects.using(schema_editor.connection.alias).all():
+        if entry.slug in slugs:
+            counter = 1
+            while(True):
+                attempt = '{}_{}'.format(entry.slug, counter)
+                if attempt not in slugs:
+                    break
+                else:
+                    counter = counter + 1
+
+            entry.slug = attempt
+            entry.save()
+
+        slugs.append(entry.slug)
+
+
 class Migration(migrations.Migration):
 
     dependencies = [
@@ -12,6 +32,10 @@ class Migration(migrations.Migration):
     ]
 
     operations = [
+        migrations.RunPython(
+            code=operation_rename_duplicates,
+            reverse_code=migrations.RunPython.noop
+        ),
         migrations.AlterField(
             model_name='statisticresult',
             name='slug',