rrs: releases should be unique by plan and name, not just name

I missed changing this constraint when adding the plan field. We want to
be able to have the same named release on another plan.

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>

rrs/migrations/0011_release_name_unique.py

@@ -0,0 +1,23 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('rrs', '0010_recipemaintenancelink'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='release',
+            name='name',
+            field=models.CharField(max_length=100),
+        ),
+        migrations.AlterUniqueTogether(
+            name='release',
+            unique_together=set([('plan', 'name')]),
+        ),
+    ]

rrs/models.py

@@ -47,10 +47,13 @@ class MaintenancePlanLayerBranch(models.Model):
 
 class Release(models.Model):
     plan = models.ForeignKey(MaintenancePlan)
-    name = models.CharField(max_length=100, unique=True)
+    name = models.CharField(max_length=100)
     start_date = models.DateField(db_index=True)
     end_date = models.DateField(db_index=True)
 
+    class Meta:
+        unique_together = ('plan', 'name',)
+
     def get_default_milestone(self):
         return self.milestone_set.last()
 
@@ -69,8 +72,13 @@ class Release(models.Model):
     def get_current(maintplan):
         current = date.today()
         current_release = Release.get_by_date(maintplan, current)
-
-        return current_release or Release.objects.filter(plan=maintplan).order_by('-end_date')[0]
+        if current_release:
+            return current_release
+        else:
+            plan_releases = Release.objects.filter(plan=maintplan).order_by('-end_date')
+            if plan_releases:
+                return plan_releases[0]
+        return None
 
     def __str__(self):
         return '%s' % (self.name)