From faf840f924c6d8432c88c70ae949c8b14f0d72ed Mon Sep 17 00:00:00 2001
From: Paul Swartz <paulswartz@gmail.com>
Date: Mon, 25 Mar 2013 10:59:31 -0400
Subject: [PATCH] only mark a field as changed if the value has changed

Prevents spurious changes from being recorded.
---
 AUTHORS             |  1 +
 mongoengine/base.py | 14 ++++++--------
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/AUTHORS b/AUTHORS
index 82a1dfa4..3d05cc41 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -128,3 +128,4 @@ that much better:
  * Peter Teichman
  * Jakub Kot
  * Jorge Bastida
+ * Paul Swartz
\ No newline at end of file
diff --git a/mongoengine/base.py b/mongoengine/base.py
index f73af4cc..0e46248f 100644
--- a/mongoengine/base.py
+++ b/mongoengine/base.py
@@ -205,8 +205,12 @@ class BaseField(object):
     def __set__(self, instance, value):
         """Descriptor for assigning a value to a field in a document.
         """
-        instance._data[self.name] = value
-        if instance._initialised:
+        changed = False
+        if (self.name not in instance._data or
+            instance._data[self.name] != value):
+            changed = True
+            instance._data[self.name] = value
+        if changed and instance._initialised:
             instance._mark_as_changed(self.name)
 
     def error(self, message="", errors=None, field_name=None):
@@ -317,12 +321,6 @@ class ComplexBaseField(BaseField):
 
         return value
 
-    def __set__(self, instance, value):
-        """Descriptor for assigning a value to a field in a document.
-        """
-        instance._data[self.name] = value
-        instance._mark_as_changed(self.name)
-
     def to_python(self, value):
         """Convert a MongoDB-compatible type to a Python type.
         """