Fix Serializer exclude for declared fields

Author: Ryan P Kilby

rest_framework/serializers.py

@@ -1099,6 +1099,9 @@ def get_field_names(self, declared_fields, info):
         # Use the default set of field names if `Meta.fields` is not specified.
         fields = self.get_default_field_names(declared_fields, info)
 
+        # deduplicate field names (occurs when a declared fields matches a model field)
+        fields = list(OrderedDict.fromkeys(fields))
+
         if exclude is not None:
             # If `Meta.exclude` is included, then remove those fields.
             for field_name in exclude:

tests/test_model_serializer.py

@@ -908,7 +908,7 @@ class Meta:
                 model = MetaClassTestModel
                 exclude = ('text',)
 
-        assert list(ExampleSerializer().fields) == ['id', 'text']
+        assert list(ExampleSerializer().fields) == ['id']
 
 
 class Issue2704TestCase(TestCase):