Don't compare FK instances in FieldTracker

model_utils/tracker.py

@@ -4,9 +4,13 @@ from django.core.exceptions import FieldError
 
 
 class FieldInstanceTracker(object):
-    def __init__(self, instance, fields):
+    def __init__(self, instance, fields, field_map):
         self.instance = instance
         self.fields = fields
+        self.field_map = field_map
+
+    def get_field(self, field):
+        return getattr(self.instance, self.field_map[field])
 
     def set_saved_fields(self, fields=None):
         if not self.instance.pk:
@@ -19,14 +23,14 @@ class FieldInstanceTracker(object):
     def current(self, fields=None):
         if fields is None:
             fields = self.fields
-        return dict((f, getattr(self.instance, f)) for f in fields)
+        return dict((f, self.get_field(f)) for f in fields)
 
     def has_changed(self, field):
         """Returns ``True`` if field has changed from currently saved value"""
         if not self.instance.pk:
             return True
         elif field in self.saved_data:
-            return self.saved_data.get(field) != getattr(self.instance, field)
+            return self.saved_data.get(field) != self.get_field(field)
         else:
             raise FieldError('field "%s" not tracked' % field)
 
@@ -50,6 +54,12 @@ class FieldTracker(object):
     def __init__(self, fields=None):
         self.fields = fields
 
+    def set_field_map(self, cls):
+        self.field_map = dict((field, field) for field in self.fields)
+        all_fields = dict((f.name, f.attname) for f in cls._meta.local_fields)
+        self.field_map.update(**dict((k, v) for (k, v) in all_fields.items()
+                                     if k in self.field_map))
+
     def contribute_to_class(self, cls, name):
         self.name = name
         self.attname = '_%s' % name
@@ -58,11 +68,12 @@ class FieldTracker(object):
     def finalize_class(self, sender, **kwargs):
         if self.fields is None:
             self.fields = [field.attname for field in sender._meta.local_fields]
+        self.set_field_map(sender)
         models.signals.post_init.connect(self.initialize_tracker, sender=sender)
         setattr(sender, self.name, self)
 
     def initialize_tracker(self, sender, instance, **kwargs):
-        tracker = self.tracker_class(instance, self.fields)
+        tracker = self.tracker_class(instance, self.fields, self.field_map)
         setattr(instance, self.attname, tracker)
         tracker.set_saved_fields()
         self.patch_save(instance)
@@ -89,3 +100,6 @@ class ModelInstanceTracker(FieldInstanceTracker):
 
 class ModelTracker(FieldTracker):
     tracker_class = ModelInstanceTracker
+
+    def set_field_map(self, cls):
+        self.field_map = dict((field, field) for field in self.fields)