Dont change return type of Serializer.errors

We should keep `Serializer.errors`'s return type unchanged in
order to maintain backward compatibility.

The error codes will only be propagated to the `exception_handler`
or accessible through the `Serializer._errors` private attribute.

rest_framework/renderers.py

@@ -493,21 +493,6 @@ class BrowsableAPIRenderer(BaseRenderer):
             if hasattr(serializer, 'initial_data'):
                 serializer.is_valid()
 
-                # Convert ValidationError to unicode string
-                # This is mainly a hack to monkey patch the errors and make the form renderer happy...
-                errors = OrderedDict()
-                for field_name, values in serializer.errors.items():
-                    if isinstance(values, list):
-                        errors[field_name] = values
-                        continue
-
-                    errors[field_name] = []
-                    for value in values.detail:
-                        for message in value.detail:
-                            errors[field_name].append(message)
-
-                serializer._errors = errors
-
             form_renderer = self.form_renderer_class()
             return form_renderer.render(
                 serializer.data,

rest_framework/serializers.py

@@ -219,7 +219,13 @@ class BaseSerializer(Field):
                 self._errors = {}
 
         if self._errors and raise_exception:
-            raise ValidationError(self.errors)
+            return_errors = None
+            if isinstance(self._errors, list):
+                return_errors = ReturnList(self._errors, serializer=self)
+            elif isinstance(self._errors, dict):
+                return_errors = ReturnDict(self._errors, serializer=self)
+
+            raise ValidationError(return_errors)
 
         return not bool(self._errors)
 
@@ -244,12 +250,42 @@ class BaseSerializer(Field):
                 self._data = self.get_initial()
         return self._data
 
+    def _transform_to_legacy_errors(self, errors_to_transform):
+        # Do not mutate `errors_to_transform` here.
+        errors = ReturnDict(serializer=self)
+        for field_name, values in errors_to_transform.items():
+            if isinstance(values, list):
+                errors[field_name] = values
+                continue
+
+            if isinstance(values.detail, list):
+                errors[field_name] = []
+                for value in values.detail:
+                    if isinstance(value, ValidationError):
+                        errors[field_name].extend(value.detail)
+                    elif isinstance(value, list):
+                        errors[field_name].extend(value)
+                    else:
+                        errors[field_name].append(value)
+
+            elif isinstance(values.detail, dict):
+                errors[field_name] = {}
+                for sub_field_name, value in values.detail.items():
+                    errors[field_name][sub_field_name] = []
+                    for validation_error in value:
+                        errors[field_name][sub_field_name].extend(validation_error.detail)
+        return errors
+
     @property
     def errors(self):
         if not hasattr(self, '_errors'):
             msg = 'You must call `.is_valid()` before accessing `.errors`.'
             raise AssertionError(msg)
-        return self._errors
+
+        if isinstance(self._errors, list):
+            return map(self._transform_to_legacy_errors, self._errors)
+        else:
+            return self._transform_to_legacy_errors(self._errors)
 
     @property
     def validated_data(self):

rest_framework/views.py

@@ -15,7 +15,6 @@ from django.views.generic import View
 
 from rest_framework import exceptions, status
 from rest_framework.compat import set_rollback
-from rest_framework.exceptions import ValidationError, _force_text_recursive
 from rest_framework.request import Request
 from rest_framework.response import Response
 from rest_framework.settings import api_settings
@@ -70,18 +69,8 @@ def exception_handler(exc, context):
         if getattr(exc, 'wait', None):
             headers['Retry-After'] = '%d' % exc.wait
 
-        if isinstance(exc.detail, list):
-            data = _force_text_recursive([item.detail if isinstance(item, ValidationError) else item
-                                          for item in exc.detai])
-        elif isinstance(exc.detail, dict):
-            for field_name, e in exc.detail.items():
-                if hasattr(e, 'detail') and isinstance(e.detail[0], ValidationError):
-                    exc.detail[field_name] = e.detail[0].detail
-                elif isinstance(e, ValidationError):
-                    exc.detail[field_name] = e.detail
-                else:
-                    exc.detail[field_name] = e
-            data = exc.detail
+        if isinstance(exc.detail, (list, dict)):
+            data = exc.detail.serializer.errors
         else:
             data = {'detail': exc.detail}
 

tests/test_bound_fields.py

@@ -38,9 +38,12 @@ class TestSimpleBoundField:
         serializer = ExampleSerializer(data={'text': 'x' * 1000, 'amount': 123})
         serializer.is_valid()
 
+        # TODO Should we add the _errors with ValidationError to the bound_field.errors to get acces to the error code?
+        assert serializer._errors['text'].detail[0].detail == ['Ensure this field has no more than 100 characters.']
+        assert serializer._errors['text'].detail[0].code == 'max_length'
+
         assert serializer['text'].value == 'x' * 1000
-        assert serializer['text'].errors.detail[0].detail == ['Ensure this field has no more than 100 characters.']
-        assert serializer['text'].errors.detail[0].code == 'max_length'
+        assert serializer['text'].errors == ['Ensure this field has no more than 100 characters.']
         assert serializer['text'].name == 'text'
         assert serializer['amount'].value is 123
         assert serializer['amount'].errors is None

tests/test_model_serializer.py

@@ -374,7 +374,7 @@ class TestGenericIPAddressFieldValidation(TestCase):
 
         s = TestSerializer(data={'address': 'not an ip address'})
         self.assertFalse(s.is_valid())
-        self.assertEquals(1, len(s.errors['address'].detail),
+        self.assertEquals(1, len(s.errors['address']),
                           'Unexpected number of validation errors: '
                           '{0}'.format(s.errors))
 

tests/test_relations_hyperlink.py

@@ -244,8 +244,9 @@ class HyperlinkedForeignKeyTests(TestCase):
         instance = ForeignKeySource.objects.get(pk=1)
         serializer = ForeignKeySourceSerializer(instance, data=data, context={'request': request})
         self.assertFalse(serializer.is_valid())
-        self.assertEqual(serializer.errors['target'].detail, ['Incorrect type. Expected URL string, received int.'])
-        self.assertEqual(serializer.errors['target'].code, 'incorrect_type')
+        self.assertEqual(serializer.errors, {'target': ['Incorrect type. Expected URL string, received int.']})
+        self.assertEqual(serializer._errors['target'].detail, ['Incorrect type. Expected URL string, received int.'])
+        self.assertEqual(serializer._errors['target'].code, 'incorrect_type')
 
     def test_reverse_foreign_key_update(self):
         data = {'url': 'http://testserver/foreignkeytarget/2/', 'name': 'target-2', 'sources': ['http://testserver/foreignkeysource/1/', 'http://testserver/foreignkeysource/3/']}
@@ -316,8 +317,9 @@ class HyperlinkedForeignKeyTests(TestCase):
         instance = ForeignKeySource.objects.get(pk=1)
         serializer = ForeignKeySourceSerializer(instance, data=data, context={'request': request})
         self.assertFalse(serializer.is_valid())
-        self.assertEqual(serializer.errors['target'].detail, ['This field may not be null.'])
-        self.assertEqual(serializer.errors['target'].code, 'null')
+        self.assertEqual(serializer.errors, {'target': ['This field may not be null.']})
+        self.assertEqual(serializer._errors['target'].detail, ['This field may not be null.'])
+        self.assertEqual(serializer._errors['target'].code, 'null')
 
 
 class HyperlinkedNullableForeignKeyTests(TestCase):

tests/test_relations_pk.py

@@ -235,9 +235,11 @@ class PKForeignKeyTests(TestCase):
         instance = ForeignKeySource.objects.get(pk=1)
         serializer = ForeignKeySourceSerializer(instance, data=data)
         self.assertFalse(serializer.is_valid())
-        self.assertEqual(serializer.errors['target'].detail,
+        self.assertEqual(serializer.errors,
+                         {'target': ['Incorrect type. Expected pk value, received %s.' % six.text_type.__name__]})
+        self.assertEqual(serializer._errors['target'].detail,
                          ['Incorrect type. Expected pk value, received %s.' % six.text_type.__name__])
-        self.assertEqual(serializer.errors['target'].code, 'incorrect_type')
+        self.assertEqual(serializer._errors['target'].code, 'incorrect_type')
 
     def test_reverse_foreign_key_update(self):
         data = {'id': 2, 'name': 'target-2', 'sources': [1, 3]}
@@ -308,8 +310,9 @@ class PKForeignKeyTests(TestCase):
         instance = ForeignKeySource.objects.get(pk=1)
         serializer = ForeignKeySourceSerializer(instance, data=data)
         self.assertFalse(serializer.is_valid())
-        self.assertEqual(serializer.errors['target'].detail, ['This field may not be null.'])
-        self.assertEqual(serializer.errors['target'].code, 'null')
+        self.assertEqual(serializer.errors, {'target': ['This field may not be null.']})
+        self.assertEqual(serializer._errors['target'].detail, ['This field may not be null.'])
+        self.assertEqual(serializer._errors['target'].code, 'null')
 
     def test_foreign_key_with_unsaved(self):
         source = ForeignKeySource(name='source-unsaved')

tests/test_relations_slug.py

@@ -104,8 +104,9 @@ class SlugForeignKeyTests(TestCase):
         instance = ForeignKeySource.objects.get(pk=1)
         serializer = ForeignKeySourceSerializer(instance, data=data)
         self.assertFalse(serializer.is_valid())
-        self.assertEqual(serializer.errors['target'].detail, ['Object with name=123 does not exist.'])
-        self.assertEqual(serializer.errors['target'].code, 'does_not_exist')
+        self.assertEqual(serializer.errors, {'target': ['Object with name=123 does not exist.']})
+        self.assertEqual(serializer._errors['target'].detail, ['Object with name=123 does not exist.'])
+        self.assertEqual(serializer._errors['target'].code, 'does_not_exist')
 
     def test_reverse_foreign_key_update(self):
         data = {'id': 2, 'name': 'target-2', 'sources': ['source-1', 'source-3']}
@@ -177,8 +178,9 @@ class SlugForeignKeyTests(TestCase):
         instance = ForeignKeySource.objects.get(pk=1)
         serializer = ForeignKeySourceSerializer(instance, data=data)
         self.assertFalse(serializer.is_valid())
-        self.assertEqual(serializer.errors['target'].detail, ['This field may not be null.'])
-        self.assertEqual(serializer.errors['target'].code, 'null')
+        self.assertEqual(serializer.errors, {'target': ['This field may not be null.']})
+        self.assertEqual(serializer._errors['target'].detail, ['This field may not be null.'])
+        self.assertEqual(serializer._errors['target'].code, 'null')
 
 
 class SlugNullableForeignKeyTests(TestCase):

tests/test_serializer.py

@@ -32,8 +32,9 @@ class TestSerializer:
         serializer = self.Serializer(data={'char': 'abc'})
         assert not serializer.is_valid()
         assert serializer.validated_data == {}
-        assert serializer.errors['integer'].detail == ['This field is required.']
-        assert serializer.errors['integer'].code == 'required'
+        assert serializer.errors == {'integer': ['This field is required.']}
+        assert serializer._errors['integer'].detail == ['This field is required.']
+        assert serializer._errors['integer'].code == 'required'
 
     def test_partial_validation(self):
         serializer = self.Serializer(data={'char': 'abc'}, partial=True)

tests/test_serializer_bulk_update.py

@@ -71,7 +71,15 @@ class BulkCreateSerializerTests(TestCase):
         serializer = self.BookSerializer(data=data, many=True)
         self.assertEqual(serializer.is_valid(), False)
 
-        for idx, error in enumerate(serializer.errors):
+        expected_errors = [
+            {},
+            {},
+            {'id': ['A valid integer is required.']}
+        ]
+
+        self.assertEqual(serializer.errors, expected_errors)
+
+        for idx, error in enumerate(serializer._errors):
             if idx < 2:
                 self.assertEqual(error, {})
             else:

tests/test_serializer_nested.py

@@ -113,8 +113,11 @@ class TestNestedSerializerWithMany:
 
         assert not serializer.is_valid()
 
-        assert serializer.errors['not_allow_null'].detail == [serializer.error_messages['null']]
-        assert serializer.errors['not_allow_null'].code == 'null'
+        expected_errors = {'not_allow_null': [serializer.error_messages['null']]}
+        assert serializer.errors == expected_errors
+
+        assert serializer._errors['not_allow_null'].detail == [serializer.error_messages['null']]
+        assert serializer._errors['not_allow_null'].code == 'null'
 
     def test_run_the_field_validation_even_if_the_field_is_null(self):
         class TestSerializer(self.Serializer):
@@ -165,7 +168,11 @@ class TestNestedSerializerWithMany:
 
         assert not serializer.is_valid()
 
-        assert serializer.errors['not_allow_empty'].detail['non_field_errors'][0].detail == \
+        expected_errors = {
+            'not_allow_empty': {'non_field_errors': [serializers.ListSerializer.default_error_messages['empty']]}}
+        assert serializer.errors == expected_errors
+
+        assert serializer._errors['not_allow_empty'].detail['non_field_errors'][0].detail == \
             [serializers.ListSerializer.default_error_messages['empty']]
 
-        assert serializer.errors['not_allow_empty'].detail['non_field_errors'][0].code == 'empty_not_allowed'
+        assert serializer._errors['not_allow_empty'].detail['non_field_errors'][0].code == 'empty_not_allowed'

tests/test_validation.py

@@ -122,9 +122,13 @@ class TestMaxValueValidatorValidation(TestCase):
     def test_max_value_validation_serializer_fails(self):
         serializer = ValidationMaxValueValidatorModelSerializer(data={'number_value': 101})
         self.assertFalse(serializer.is_valid())
-        self.assertEqual(['Ensure this value is less than or equal to 100.'], serializer.errors['number_value'].detail[0].detail)
-        self.assertEqual(None, serializer.errors['number_value'].code)
-        self.assertEqual('max_value', serializer.errors['number_value'].detail[0].code)
+
+        self.assertDictEqual({'number_value': ['Ensure this value is less than or equal to 100.']}, serializer.errors)
+
+        self.assertEqual(['Ensure this value is less than or equal to 100.'],
+                         serializer._errors['number_value'].detail[0].detail)
+        self.assertEqual(None, serializer._errors['number_value'].code)
+        self.assertEqual('max_value', serializer._errors['number_value'].detail[0].code)
 
     def test_max_value_validation_success(self):
         obj = ValidationMaxValueValidatorModel.objects.create(number_value=100)

tests/test_validators.py

@@ -49,9 +49,12 @@ class TestUniquenessValidation(TestCase):
         serializer = UniquenessSerializer(data=data)
 
         assert not serializer.is_valid()
-        assert serializer.errors['username'].code is None
-        assert serializer.errors['username'].detail[0].code == 'unique'
-        assert serializer.errors['username'].detail[0].detail == ['UniquenessModel with this username already exists.']
+
+        assert serializer.errors == {'username': ['UniquenessModel with this username already exists.']}
+
+        assert serializer._errors['username'].code is None
+        assert serializer._errors['username'].detail[0].code == 'unique'
+        assert serializer._errors['username'].detail[0].detail == ['UniquenessModel with this username already exists.']
 
     def test_is_unique(self):
         data = {'username': 'other'}