(devhub/dhplatform#8780) updates to save_instance

baph/forms/forms.py

@@ -39,6 +39,7 @@
 
 orm = ORM.get()
 
+
 def save_instance(form, instance, fields=None, fail_message='saved',
                   commit=True, exclude=None):
     """
@@ -48,16 +49,23 @@ def save_instance(form, instance, fields=None, fail_message='saved',
     database. Returns ``instance``.
     """
     opts = instance._meta
-    for k,v in form.cleaned_data.items():
-        if k in form.data:
-            try:
-                # TODO: this fails when trying to reach the remote side
-                # of an association_proxy when the interim node is None
-                # find a better solution
-                setattr(instance, k, v)
-            except TypeError as e:
-                continue
-
+    for k, v in form.cleaned_data.items():
+        if k not in form.data:
+            # ignore values that weren't submitted
+            continue
+        current = getattr(instance, k, None)
+        if current == v:
+            # value is unchanged
+            continue
+
+        try:
+            # TODO: this fails when trying to reach the remote side
+            # of an association_proxy when the interim node is None
+            # find a better solution
+            setattr(instance, k, v)
+        except TypeError:
+            continue
+
     if form.errors:
         raise ValueError("The %s could not be %s because the data didn't"
                          " validate." % (opts.object_name, fail_message))