Fixed #16612 -- Improved has_changed detection for localized field values

Thanks Simon Charette for the review.

3 files changed, 24 insertions, 18 deletions

diff --git a/django/forms/fields.py b/django/forms/fields.py
index 277f0b093e..c7ed085b16 100644
--- a/django/forms/fields.py
+++ b/django/forms/fields.py
@@ -184,17 +184,13 @@ class Field(object):
         # For purposes of seeing whether something has changed, None is
         # the same as an empty string, if the data or inital value we get
         # is None, replace it w/ ''.
-        if data is None:
-            data_value = ''
-        else:
-            data_value = data
-        if initial is None:
-            initial_value = ''
-        else:
-            initial_value = initial
-        if force_text(initial_value) != force_text(data_value):
+        initial_value = initial if initial is not None else ''
+        try:
+            data = self.to_python(data)
+        except ValidationError:
             return True
-        return False
+        data_value = data if data is not None else ''
+        return initial_value != data_value
 
     def __deepcopy__(self, memo):
         result = copy.copy(self)
@@ -392,12 +388,6 @@ class BaseTemporalField(Field):
     def strptime(self, value, format):
         raise NotImplementedError('Subclasses must define this method.')
 
-    def _has_changed(self, initial, data):
-        try:
-            data = self.to_python(data)
-        except ValidationError:
-            return True
-        return self.to_python(initial) != data
 
 class DateField(BaseTemporalField):
     widget = DateInput
diff --git a/django/forms/forms.py b/django/forms/forms.py
index 20a2e426bb..38601432bc 100644
--- a/django/forms/forms.py
+++ b/django/forms/forms.py
@@ -345,8 +345,8 @@ class BaseForm(object):
                 else:
                     initial_prefixed_name = self.add_initial_prefix(name)
                     hidden_widget = field.hidden_widget()
-                    initial_value = hidden_widget.value_from_datadict(
-                        self.data, self.files, initial_prefixed_name)
+                    initial_value = field.to_python(hidden_widget.value_from_datadict(
+                        self.data, self.files, initial_prefixed_name))
                 if hasattr(field.widget, '_has_changed'):
                     warnings.warn("The _has_changed method on widgets is deprecated,"
                         " define it at field level instead.",
diff --git a/django/forms/models.py b/django/forms/models.py
index 3905e9e902..1cea110df4 100644
--- a/django/forms/models.py
+++ b/django/forms/models.py
@@ -1012,6 +1012,11 @@ class ModelChoiceField(ChoiceField):
     def validate(self, value):
         return Field.validate(self, value)
 
+    def _has_changed(self, initial, data):
+        initial_value = initial if initial is not None else ''
+        data_value = data if data is not None else ''
+        return force_text(self.prepare_value(initial_value)) != force_text(data_value)
+
 class ModelMultipleChoiceField(ModelChoiceField):
     """A MultipleChoiceField whose choices are a model QuerySet."""
     widget = SelectMultiple
@@ -1059,3 +1064,14 @@ class ModelMultipleChoiceField(ModelChoiceField):
                 not hasattr(value, '_meta')):
             return [super(ModelMultipleChoiceField, self).prepare_value(v) for v in value]
         return super(ModelMultipleChoiceField, self).prepare_value(value)
+
+    def _has_changed(self, initial, data):
+        if initial is None:
+            initial = []
+        if data is None:
+            data = []
+        if len(initial) != len(data):
+            return True
+        initial_set = set([force_text(value) for value in initial])
+        data_set = set([force_text(value) for value in data])
+        return data_set != initial_set