django-mptt-filter-before-and-after.diff

diff --git a/mptt/managers.py b/mptt/managers.py
index e7893af..8290443 100644
--- a/mptt/managers.py
+++ b/mptt/managers.py
@@ -2,7 +2,7 @@
 A custom manager for working with trees of objects.
 """
 from django.db import connection, models, transaction
-from django.db.models import F, Max
+from django.db.models import F, Max, Q
 from django.utils.translation import ugettext as _
 
 try:
@@ -160,6 +160,38 @@ class TreeManager(models.Manager):
         """
         return super(TreeManager, self).get_query_set().order_by(
             self.tree_id_attr, self.left_attr)
+    
+    def filter_after(self, queryset, obj):
+        """
+        Returns the given queryset filtered by nodes that come (in normal tree order)
+        AFTER the given node. The queryset ordering is not changed.
+        """
+        return queryset.filter(
+            # WHERE (lft > obj.rght AND tree_id = obj.tree_id)
+            Q(**{
+                '%s__gt' % self.left_attr : getattr(obj, self.right_attr),
+                self.tree_id_attr : getattr(obj, self.tree_id_attr),
+            })
+            
+            # OR (tree_id > obj.tree_id)
+            | Q(**{'%s__gt' % self.tree_id_attr : getattr(obj, self.tree_id_attr)})
+        )
+    
+    def filter_before(self, queryset, obj):
+        """
+        Returns the given queryset filtered by nodes that come (in normal tree order)
+        BEFORE the given node. The queryset ordering is not changed.
+        """
+        return queryset.filter(
+            # WHERE (rght < obj.lft AND tree_id = obj.tree_id)
+            Q(**{
+                '%s__lt' % self.right_attr : getattr(obj, self.left_attr),
+                self.tree_id_attr : getattr(obj, self.tree_id_attr),
+            })
+            
+            # OR (tree_id < obj.tree_id)
+            | Q(**{'%s__lt' % self.tree_id_attr : getattr(obj, self.tree_id_attr)})
+        )
 
     def insert_node(self, node, target, position='last-child', save=False):
         """
diff --git a/mptt/models.py b/mptt/models.py
index 4fb37a8..d8d3306 100644
--- a/mptt/models.py
+++ b/mptt/models.py
@@ -267,6 +267,20 @@ class MPTTModel(models.Model):
 
         siblings = qs[:1]
         return siblings and siblings[0] or None
+    
+    def get_next_node(self):
+        """
+        Returns the next node in the tree (in tree order)
+        """
+        qs = self._tree_manager.filter_after(self._tree_manager.all(), self)
+        return qs.order_by('tree_id', 'lft')[:1].get()
+    
+    def get_previous_node(self):
+        """
+        Returns the previous node in the tree (in tree order)
+        """
+        qs = self._tree_manager.filter_before(self._tree_manager.all(), self)
+        return qs.order_by('-tree_id', '-lft')[:1].get()
 
     def get_root(self):
         """