Added depth attribute to hold the level of a node relative to its roo…

…t node

posts/migrations/0002_post_depth.py

@@ -0,0 +1,19 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import models, migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('posts', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='post',
+            name='depth',
+            field=models.PositiveSmallIntegerField(default=0),
+        ),
+    ]

posts/models.py

@@ -13,6 +13,7 @@ class Post(models.Model):
     slug = models.SlugField()
     created = models.DateTimeField(auto_now_add=True)
     updated = models.DateTimeField(auto_now=True)
+    depth = models.PositiveSmallIntegerField(default=0)
 
     # Foreign Keys
     thread = models.ForeignKey('threads.Thread')
@@ -29,4 +30,9 @@ def __unicode__(self):
 def generate_slug(sender, instance, created, **kwargs):
     if created:
         instance.slug = HASHER.encode(instance.pk)
+        # Calculate the depth for a comment, root nodes are 0 and those with
+        # children take their parent's depth value plus one.
+        depth = 0 if instance.parent is None else instance.parent.depth + 1
+        instance.depth = depth
+
         instance.save()

posts/tests/test_models.py

@@ -33,3 +33,10 @@ def test_thread_created_date_and_updated_date(self, mock_now):
             message='Post', thread=self.thread, parent=None)
         self.assertEqual(p.created, datetime.datetime(2015, 1, 1))
         self.assertEqual(p.updated, datetime.datetime(2015, 1, 1))
+
+    def test_post_depth(self):
+        self.assertEqual(self.post.depth, 0)
+
+        p = Post.objects.create(
+            message='A Child', thread=self.thread, parent=self.post)
+        self.assertEqual(p.depth, 1)