Get value of another field in Field level Validation in DRF

Question

I am using Field level Validation in my serializer and I have situation where I need value of first field while validating second field. I know in object level validation I can have access to that but my serailzer have many=True and in object level validation I cannot tell client side which iteration have raised the error.

Serailzer :

class Keys_Serializer(serializers.Serializer):
    """
    """
    key_id = serializers.IntegerField(required=True)
    key_name = serializers.CharField(required=True)
    value_id = serializers.IntegerField(required=False)

    def validate_key_id(self, value):
        """
        validate key id
        """
         *** validate key_id here ***
        return value

    def validate_value_id(self, value):
        """
        validate value_id w.r.t key_id
        """
         *** I need key_id of current iteration here so that I can validate value_id. ***
        return value

Is there any way of accessing the value of key_id in value_id validation.

Answer 1

No that is not possible. If you need to access more than one value you have to use the Object-level validation (see docs):

class Keys_Serializer(serializers.Serializer):

    key_id = serializers.IntegerField(required=True)
    key_name = serializers.CharField(required=True)
    value_id = serializers.IntegerField(required=False)

    def validate(self, data):
        # here you can access all values
        key_id = data['key_id']
        value_id = data['value_id']
        # perform you validation
        if key_id != value_id:
            raise serializers.ValidationError("key_id must be equal to value_id")
        return data

Answer 2

I dug around codebase of drf a little bit. You can get values of all fields using following approach. This way you can throw serialization error as {'my_field':'error message} instead of {'non_field_error':'error message'}

def validate_myfield(self, value):
   data = self.get_initial() # data for all the fields
   #do your validation

However, if you wish to do it for ListSerializer, i.e for serializer = serializer_class(many=True), this won't work. You will get list of empty values. In that scenario, you could write your validations in def validate function and to avoid non_field_errors in your serialization error, you can raise ValidationError with error message as a dictionary instead of string.

def validate(self, data):
    # do your validation
    raise serializers.ValidationError({"your_field": "error_message"})