Support calling EnumField.to_representation() with choice key as value

rest_framework_dataclasses/fields.py

@@ -31,6 +31,13 @@ def to_internal_value(self, data):
             self.fail('invalid_choice', input=data)
 
     def to_representation(self, value):
+        # Some external libraries expect to be able to call to_representation() with the key from the choices
+        # array, which seems at least somewhat reasonable. See #40.
+        if not isinstance(value, self.enum_class):
+            if value in self.choices:
+                return value
+            self.fail('invalid_choice', input=value)
+
         if self.by_name:
             return value.name
         else:

tests/test_fields.py

@@ -36,3 +36,7 @@ class Color(enum.Enum):
         self.assertEqual(field.to_representation(Color.GREEN), 'GREEN')
         with self.assertRaises(ValidationError):
             field.to_internal_value('FF0000')
+
+        self.assertEqual(field.to_representation('RED'), 'RED')
+        with self.assertRaises(ValidationError):
+            field.to_representation('FFFFFF')