1 files changed, 43 insertions, 0 deletions
diff --git a/postgresqleu/util/diffablemodel.py b/postgresqleu/util/diffablemodel.py
new file mode 100644
index 00000000..7a38c7b0
--- /dev/null
+++ b/postgresqleu/util/diffablemodel.py
@@ -0,0 +1,43 @@
+from django.forms.models import model_to_dict
+import django.db.models.fields.related
+
+
+class DiffableModel(object):
+	"""
+	Make it possible to diff a model.
+    """
+
+	def __init__(self, *args, **kwargs):
+		super(DiffableModel, self).__init__(*args, **kwargs)
+		self.__initial = self._dict
+
+	@property
+	def diff(self):
+		manytomanyfieldnames = [f.name for f in self._meta.many_to_many]
+		d1 = self.__initial
+		d2 = self._dict
+		diffs = dict([(k, (v, d2[k])) for k, v in d1.items() if v != d2[k]])
+		# Foreign key lookups
+		for k,v in diffs.items():
+			if type(self._meta.get_field_by_name(k)[0]) is django.db.models.fields.related.ForeignKey:
+				# If it's a foreign key, look up the name again on ourselves.
+				# Since we only care about the *new* value, it's easy enough.
+				diffs[k] = (v[0], getattr(self, k))
+		# Many to many lookups
+		if hasattr(self, 'map_manytomany_for_diff'):
+			for k,v in diffs.items():
+				if k in manytomanyfieldnames and self.map_manytomany_for_diff.has_key(k):
+					# Try to show the display name instead here
+					newvalue = getattr(self, self.map_manytomany_for_diff[k])
+					diffs[k] = (v[0], newvalue)
+		return diffs
+
+	def save(self, *args, **kwargs):
+		super(DiffableModel, self).save(*args, **kwargs)
+		self.__initial = self._dict
+
+	@property
+	def _dict(self):
+		fields = [field.name for field in self._meta.fields]
+		fields.extend([field.name for field in self._meta.many_to_many])
+		return model_to_dict(self, fields=fields)