transport: avoid index issues with MySQL/MariaDB.

See https://github.com/modoboa/modoboa-postfix-autoreply/issues/19

modoboa/transport/migrations/0002_auto_20180928_1520.py

@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.15 on 2018-09-28 13:20
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('transport', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='transport',
+            name='pattern',
+            field=models.CharField(db_index=True, max_length=253, unique=True, verbose_name='pattern'),
+        ),
+    ]

modoboa/transport/models.py

@@ -16,7 +16,8 @@ from . import backends
 class Transport(models.Model):
     """Transport table."""
 
-    pattern = models.CharField(_("pattern"), unique=True, max_length=254)
+    pattern = models.CharField(
+        _("pattern"), unique=True, max_length=253, db_index=True)
     service = models.CharField(_("service"), max_length=30)
     next_hop = models.CharField(_("next hop"), max_length=100, blank=True)