Fixed #16192 -- Made unique error messages in ModelForm customizable.

Overriding the error messages now works for both unique fields, unique_together
and unique_for_date.

This patch changed the overriding logic to allow customizing NON_FIELD_ERRORS
since previously only fields' errors were customizable.

Refs #20199.

Thanks leahculver for the suggestion.

django/db/models/base.py

@@ -941,36 +941,52 @@ class Model(six.with_metaclass(ModelBase)):
                 )
         return errors
 
-    def date_error_message(self, lookup_type, field, unique_for):
+    def date_error_message(self, lookup_type, field_name, unique_for):
         opts = self._meta
-        return _("%(field_name)s must be unique for %(date_field)s %(lookup)s.") % {
-            'field_name': six.text_type(capfirst(opts.get_field(field).verbose_name)),
-            'date_field': six.text_type(capfirst(opts.get_field(unique_for).verbose_name)),
-            'lookup': lookup_type,
-        }
+        field = opts.get_field(field_name)
+        return ValidationError(
+            message=field.error_messages['unique_for_date'],
+            code='unique_for_date',
+            params={
+                'model': self,
+                'model_name': six.text_type(capfirst(opts.verbose_name)),
+                'lookup_type': lookup_type,
+                'field': field_name,
+                'field_label': six.text_type(capfirst(field.verbose_name)),
+                'date_field': unique_for,
+                'date_field_label': six.text_type(capfirst(opts.get_field(unique_for).verbose_name)),
+            }
+        )
 
     def unique_error_message(self, model_class, unique_check):
         opts = model_class._meta
-        model_name = capfirst(opts.verbose_name)
+
+        params = {
+            'model': self,
+            'model_class': model_class,
+            'model_name': six.text_type(capfirst(opts.verbose_name)),
+            'unique_check': unique_check,
+        }
 
         # A unique field
         if len(unique_check) == 1:
-            field_name = unique_check[0]
-            field = opts.get_field(field_name)
-            field_label = capfirst(field.verbose_name)
-            # Insert the error into the error dict, very sneaky
-            return field.error_messages['unique'] % {
-                'model_name': six.text_type(model_name),
-                'field_label': six.text_type(field_label)
-            }
+            field = opts.get_field(unique_check[0])
+            params['field_label'] = six.text_type(capfirst(field.verbose_name))
+            return ValidationError(
+                message=field.error_messages['unique'],
+                code='unique',
+                params=params,
+            )
+
         # unique_together
         else:
             field_labels = [capfirst(opts.get_field(f).verbose_name) for f in unique_check]
-            field_labels = get_text_list(field_labels, _('and'))
-            return _("%(model_name)s with this %(field_label)s already exists.") % {
-                'model_name': six.text_type(model_name),
-                'field_label': six.text_type(field_labels)
-            }
+            params['field_labels'] = six.text_type(get_text_list(field_labels, _('and')))
+            return ValidationError(
+                message=_("%(model_name)s with this %(field_labels)s already exists."),
+                code='unique_together',
+                params=params,
+            )
 
     def full_clean(self, exclude=None, validate_unique=True):
         """

django/db/models/fields/__init__.py

@@ -105,6 +105,8 @@ class Field(RegisterLookupMixin):
         'blank': _('This field cannot be blank.'),
         'unique': _('%(model_name)s with this %(field_label)s '
                     'already exists.'),
+        'unique_for_date': _("%(field_label)s must be unique for "
+                             "%(date_field_label)s %(lookup_type)s."),
     }
     class_lookups = default_lookups.copy()
 

django/forms/forms.py

@@ -8,7 +8,7 @@ from collections import OrderedDict
 import copy
 import warnings
 
-from django.core.exceptions import ValidationError
+from django.core.exceptions import ValidationError, NON_FIELD_ERRORS
 from django.forms.fields import Field, FileField
 from django.forms.utils import flatatt, ErrorDict, ErrorList
 from django.forms.widgets import Media, MediaDefiningClass, TextInput, Textarea
@@ -21,8 +21,6 @@ from django.utils import six
 
 __all__ = ('BaseForm', 'Form')
 
-NON_FIELD_ERRORS = '__all__'
-
 
 def pretty_name(name):
     """Converts 'first_name' to 'First name'"""

django/forms/models.py

@@ -373,15 +373,21 @@ class BaseModelForm(BaseForm):
 
     def _update_errors(self, errors):
         # Override any validation error messages defined at the model level
-        # with those defined on the form fields.
+        # with those defined at the form level.
+        opts = self._meta
         for field, messages in errors.error_dict.items():
-            if field not in self.fields:
+            if (field == NON_FIELD_ERRORS and opts.error_messages and
+                    NON_FIELD_ERRORS in opts.error_messages):
+                error_messages = opts.error_messages[NON_FIELD_ERRORS]
+            elif field in self.fields:
+                error_messages = self.fields[field].error_messages
+            else:
                 continue
-            field = self.fields[field]
+
             for message in messages:
                 if (isinstance(message, ValidationError) and
-                        message.code in field.error_messages):
-                    message.message = field.error_messages[message.code]
+                        message.code in error_messages):
+                    message.message = error_messages[message.code]
 
         self.add_error(None, errors)