DictField key validation

[snowman2]

https://stackoverflow.com/questions/75148782/django-rest-framework-serializers-dictfield-constraint-on-possible-keys

Something like serializers.DictField(key=serializers.ChoiceField(choices=[enum.value for enum in Enum])) would be great but that's obviously not available.

It would also be nice to run validators on the keys as well. Adding key as serializer Field would enable that in a more DRF way of doing things.

[Natgho]

That could be a good approach. To support this, we’ll just need to extend the logic of DictField a bit. If we add an argument named key_field to DictField, it will continue to use the default behavior if not provided, but if provided, it can use this method. It’s easier to show this in code than to explain it;

class DictField(Field):
    def __init__(self, key_field=None, child=None, **kwargs):
        self.key_field = key_field
        self.child = child
        super().__init__(**kwargs)
        if self.key_field:
            self.key_field.bind(field_name='', parent=self)

and deserialization part;

def to_internal_value(self, data):
        if not isinstance(data, dict):
            self.fail('not_a_dict', input_type=type(data).__name__)
        
        ret = {}
        for key, value in data.items():
            # 1. key validation
            if self.key_field:
                try:
                    validated_key = self.key_field.run_validation(key)
                except ValidationError as e:
                    raise ValidationError({key: e.detail})
            else:
                validated_key = str(key)

            # 2. value validation
            if self.child:
                ret[validated_key] = self.child.run_validation(value)
            else:
                ret[validated_key] = value
        return ret

For example, this idea also provides the DRF with the following flexibility:

def validate_prefix(value):
    if not value.startswith('attr_'):
        raise serializers.ValidationError("Key should start with 'attr_' ")

class DynamicAttributesSerializer(serializers.Serializer):
    attributes = serializers.DictField(
        key_field=serializers.CharField(validators=[validate_prefix]),
        child=serializers.CharField()
    )

That sounds like a reasonable and good suggestion to me. It would be nice to hear the maintainers’ thoughts as well.
Note: If the idea is accepted, I can take on the development work. @auvipy @browniebroke