Allow overriding field mappings for choice field

rest_framework/fields.py

@@ -1412,13 +1412,12 @@ class ChoiceField(Field):
     html_cutoff = None
     html_cutoff_text = _('More than {count} items...')
 
-    def __init__(self, choices, **kwargs):
+    def __init__(self, choices, allow_blank=False, **kwargs):
         self.choices = choices
+        self.allow_blank = allow_blank
         self.html_cutoff = kwargs.pop('html_cutoff', self.html_cutoff)
         self.html_cutoff_text = kwargs.pop('html_cutoff_text', self.html_cutoff_text)
 
-        self.allow_blank = kwargs.pop('allow_blank', False)
-
         super().__init__(**kwargs)
 
     def to_internal_value(self, data):

rest_framework/serializers.py

@@ -1212,20 +1212,19 @@ class ModelSerializer(Serializer):
             field_class = self.serializer_related_field
             field_kwargs['queryset'] = model_field.related_model.objects
 
-        if 'choices' in field_kwargs:
+        if 'choices' in field_kwargs and not issubclass(field_class, self.serializer_choice_field):
             # Fields with choices get coerced into `ChoiceField`
             # instead of using their regular typed field.
             field_class = self.serializer_choice_field
             # Some model fields may introduce kwargs that would not be valid
             # for the choice field. We need to strip these out.
             # Eg. models.DecimalField(max_digits=3, decimal_places=1, choices=DECIMAL_CHOICES)
-            valid_kwargs = {
-                'read_only', 'write_only',
-                'required', 'default', 'initial', 'source',
-                'label', 'help_text', 'style',
-                'error_messages', 'validators', 'allow_null', 'allow_blank',
-                'choices'
-            }
+            valid_kwargs = set()
+            for c in inspect.getmro(field_class):
+                sig = inspect.signature(c.__init__)
+                for param in sig.parameters.values():
+                    if (param.kind == param.POSITIONAL_OR_KEYWORD):
+                        valid_kwargs.add(param.name)
             for key in list(field_kwargs):
                 if key not in valid_kwargs:
                     field_kwargs.pop(key)

tests/test_model_serializer.py

@@ -217,6 +217,25 @@ class TestRegularFieldMappings(TestCase):
         """)
         self.assertEqual(repr(TestSerializer()), expected)
 
+    def test_override_choice_field_mapping(self):
+        class CustomChoiceField(models.CharField):
+            """
+            A custom choice model field simply for testing purposes.
+            """
+            max_length = 100
+
+        class CostomizedChoiceModel(models.Model):
+            choices_field = CustomChoiceField(choices=COLOR_CHOICES)
+
+        class TestSerializer(serializers.ModelSerializer):
+            class Meta:
+                model = CostomizedChoiceModel
+                fields = '__all__'
+
+        self.assertTrue(isinstance(TestSerializer().fields["choices_field"], serializers.ChoiceField))
+        TestSerializer.serializer_field_mapping[CustomChoiceField] = serializers.MultipleChoiceField
+        self.assertTrue(isinstance(TestSerializer().fields["choices_field"], serializers.MultipleChoiceField))
+
     def test_nullable_boolean_field_choices(self):
         class NullableBooleanChoicesModel(models.Model):
             CHECKLIST_OPTIONS = (