Update ModelSerializer fields behavior

rest_framework/serializers.py

@@ -12,6 +12,8 @@ response content is handled by parsers and renderers.
 """
 from __future__ import unicode_literals
 
+import warnings
+
 from django.db import models
 from django.db.models.fields import Field as DjangoModelField
 from django.db.models.fields import FieldDoesNotExist
@@ -51,6 +53,8 @@ LIST_SERIALIZER_KWARGS = (
     'instance', 'data', 'partial', 'context', 'allow_null'
 )
 
+ALL_FIELDS = '__all__'
+
 
 # BaseSerializer
 # --------------
@@ -943,13 +947,13 @@ class ModelSerializer(Serializer):
         fields = getattr(self.Meta, 'fields', None)
         exclude = getattr(self.Meta, 'exclude', None)
 
-        if fields and not isinstance(fields, (list, tuple)):
+        if fields and fields != ALL_FIELDS and not isinstance(fields, (list, tuple)):
             raise TypeError(
                 'The `fields` option must be a list or tuple. Got %s.' %
                 type(fields).__name__
             )
 
-        if exclude and not isinstance(exclude, (list, tuple)):
+        if exclude and exclude != ALL_FIELDS and not isinstance(exclude, (list, tuple)):
             raise TypeError(
                 'The `exclude` option must be a list or tuple. Got %s.' %
                 type(exclude).__name__
@@ -962,6 +966,19 @@ class ModelSerializer(Serializer):
             )
         )
 
+        if fields is None and exclude is None:
+            warnings.warn(
+                "Creating a ModelSerializer without either the 'fields' attribute "
+                "or the 'exclude' attribute will be prohibited. "
+                "The {serializer_class} serializer needs updating.".format(
+                    serializer_class=self.__class__.__name__
+                ),
+                PendingDeprecationWarning
+            )
+
+        if fields == ALL_FIELDS:
+            fields = None
+
         if fields is not None:
             # Ensure that all declared fields have also been included in the
             # `Meta.fields` option.

tests/test_model_serializer.py

@@ -321,6 +321,21 @@ class TestRegularFieldMappings(TestCase):
 
         ExampleSerializer()
 
+    def test_fields_and_exclude_behavior(self):
+        class ImplicitFieldsSerializer(serializers.ModelSerializer):
+            class Meta:
+                model = RegularFieldsModel
+
+        class ExplicitFieldsSerializer(serializers.ModelSerializer):
+            class Meta:
+                model = RegularFieldsModel
+                fields = '__all__'
+
+        implicit = ImplicitFieldsSerializer()
+        explicit = ExplicitFieldsSerializer()
+
+        assert implicit.data == explicit.data
+
 
 @pytest.mark.skipif(django.VERSION < (1, 8),
                     reason='DurationField is only available for django1.8+')