Merge pull request #28 from jjkester/improved-diffs

Improve diffs

.travis.yml

@@ -9,3 +9,4 @@ install:
   - "pip install -r requirements.txt"
   - "pip install Django==$DJANGO_VERSION"
 script: "python src/runtests.py"
+sudo: false

src/auditlog/diff.py

@@ -1,15 +1,58 @@
 from __future__ import unicode_literals
 
 from django.core.exceptions import ObjectDoesNotExist
-from django.db.models import Model
+from django.db.models import Model, NOT_PROVIDED
 from django.utils.encoding import smart_text
 
 
+def track_field(field):
+    """
+    Returns whether the given field should be tracked by Auditlog.
+
+    Untracked fields are many-to-many relations and relations to the Auditlog LogEntry model.
+
+    :param field: The field to check.
+    :type field: Field
+    :return: Whether the given field should be tracked.
+    :rtype: bool
+    """
+    from auditlog.models import LogEntry
+    # Do not track many to many relations
+    if field.many_to_many:
+        return False
+
+    # Do not track relations to LogEntry
+    if getattr(field, 'rel', None) is not None and field.rel.to == LogEntry:
+        return False
+
+    return True
+
+
+def get_fields_in_model(instance):
+    """
+    Returns the list of fields in the given model instance. Checks whether to use the official _meta API or use the raw
+    data. This method excludes many to many fields.
+
+    :param instance: The model instance to get the fields for
+    :type instance: Model
+    :return: The list of fields for the given model (instance)
+    :rtype: list
+    """
+    assert isinstance(instance, Model)
+
+    # Check if the Django 1.8 _meta API is available
+    use_api = hasattr(instance._meta, 'get_fields') and callable(instance._meta.get_fields)
+
+    if use_api:
+        return [f for f in instance._meta.get_fields() if track_field(f)]
+    return instance._meta.fields
+
+
 def model_instance_diff(old, new, **kwargs):
     """
     Calculate the differences between two model instances. One of the instances may be None (i.e., a newly
-    created model or deleted model). This will cause all fields with a value to have changed (from None).
-
+    created model or deleted model). This will cause all fields with a value to have changed (from the fields default
+    value).
     """
     from auditlog.registry import auditlog
 
@@ -21,13 +64,13 @@ def model_instance_diff(old, new, **kwargs):
     diff = {}
 
     if old is not None and new is not None:
-        fields = set(old._meta.fields + new._meta.fields)
+        fields = set(get_fields_in_model(old) + get_fields_in_model(new))
         model_fields = auditlog.get_model_fields(new._meta.model)
     elif old is not None:
-        fields = set(old._meta.fields)
+        fields = set(get_fields_in_model(old))
         model_fields = auditlog.get_model_fields(old._meta.model)
     elif new is not None:
-        fields = set(new._meta.fields)
+        fields = set(get_fields_in_model(new))
         model_fields = auditlog.get_model_fields(new._meta.model)
     else:
         fields = set()
@@ -48,17 +91,17 @@ def model_instance_diff(old, new, **kwargs):
 
     for field in fields:
         try:
-            old_value = smart_text(getattr(old, field.name, None))
+            old_value = getattr(old, field.name, None)
         except ObjectDoesNotExist:
-            old_value = None
+            old_value = field.default if field.default is not NOT_PROVIDED else None
 
         try:
-            new_value = smart_text(getattr(new, field.name, None))
+            new_value = getattr(new, field.name, None)
         except ObjectDoesNotExist:
             new_value = None
 
         if old_value != new_value:
-            diff[field.name] = (old_value, new_value)
+            diff[field.name] = (smart_text(old_value), smart_text(new_value))
 
     if len(diff) == 0:
         diff = None