Make the statistics slug field unique

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

HISTORY.rst

@@ -147,6 +147,7 @@
 - Add workflow action to sign documents.
 - Support running specific tests inside the Docker container.
   docker run --rm mayanedms/mayanedms:3.3 run_tests
+- Make the statistics slug field unique.
 
 3.2.10 (2019-XX-XX)
 ===================

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

@@ -0,0 +1,20 @@
+# -*- 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
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('mayan_statistics', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='statisticresult',
+            name='slug',
+            field=models.SlugField(unique=True, verbose_name='Slug'),
+        ),
+    ]

mayan/apps/mayan_statistics/models.py

@@ -11,7 +11,7 @@ from django.utils.translation import ugettext_lazy as _
 class StatisticResult(models.Model):
     # Translators: 'Slug' refers to the URL valid ID of the statistic
     # More info: https://docs.djangoproject.com/en/1.7/glossary/#term-slug
-    slug = models.SlugField(verbose_name=_('Slug'))
+    slug = models.SlugField(unique=True, verbose_name=_('Slug'))
     datetime = models.DateTimeField(
         auto_now=True, verbose_name=_('Date time')
     )