Validation codes and messages in Django Rest Framework

Question

Using out of the box fields in a serializer, validation error messages look something like this:

{
    "product": [
        "This field must be unique."
    ],
    "price": [
        "This field is required."
    ]
}

However, for the API I am writing, I would like to provide a unique error code for each failed validation, so that clients can programmatically respond to validation errors, or can provide their own custom messages in a UI. Ideally the error json would look something like this:

{
    "product": [
        {
          "code": "unique",
          "message": "This field must be unique."
        }
    ],
    "price": [
        { 
          "code": "required",
          "message": "This field is required."
        }
    ]
}

The current approach using ValidationErrors makes this rather difficult. Looking through the code, it seems as though this type of error reporting is not supported currently. However, I'm looking for an approach to override the error handling to fit this model.

Answer 1

This question was posted quite a while ago, so I will add the updated answer here. Newer versions of DRF now support this, but it still takes a bit of custom code. Creating a new exception handler with do the trick:

from rest_framework.views import exception_handler
from rest_framework.exceptions import APIException


def full_details_exception_handler(exc, context):
    """
    This overrides the default exception handler to
    include the human-readable message AND the error code
    so that clients can respond programmatically.
    """
    if isinstance(exc, APIException):
        exc.detail = exc.get_full_details()

    return exception_handler(exc, context)

Then configure DRF to use that custom handler in your settings:

REST_FRAMEWORK['EXCEPTION_HANDLER'] = 'my_module.full_details_exception_handler'

It would be nice if this configuration were available in DRF itself to just add it as a configuration option, but this is a pretty lightweight solution to include the error codes.

Answer 2

Add something like this to your serializer:

def is_valid(self, raise_exception=False):
    try:
        return super(ClientSerializer, self).is_valid(raise_exception)
    except exceptions.ValidationError as e:
        if 'email' in e.detail:
            for i in range(len(e.detail['email'])):
                if e.detail['email'][i] == UniqueValidator.message:
                    e.detail['email'][i] = {'code': 'not-unique'}
        raise e