In each case, REST framework will return a response with an appropriate status code and content-type. The body of the response will include any additional details regarding the nature of the error.
Validation errors are handled slightly differently, and will include the field names as the keys in the response. If the validation error was not specific to a particular field then it will use the "non_field_errors" key, or whatever string value has been set for the `NON_FIELD_ERRORS_KEY` setting.
Any example validation error might look like this:
HTTP/1.1 400 Bad Request
Content-Type: application/json
Content-Length: 94
{"amount": ["A valid integer is required."], "description": ["This field may not be blank."]}
You can implement custom exception handling by creating a handler function that converts exceptions raised in your API views into response objects. This allows you to control the style of error responses used by your API.
The function must take a pair of arguments, this first is the exception to be handled, and the second is a dictionary containing any extra context such as the view currently being handled. The exception handler function should either return a `Response` object, or return `None` if the exception cannot be handled. If the handler returns `None` then the exception will be re-raised and Django will return a standard HTTP 500 'server error' response.
The context argument is not used by the default handler, but can be useful if the exception handler needs further information such as the view currently being handled, which can be accessed as `context['view']`.
Note that the exception handler will only be called for responses generated by raised exceptions. It will not be used for any responses returned directly by the view, such as the `HTTP_400_BAD_REQUEST` responses that are returned by the generic views when serializer validation fails.
For example, if your API relies on a third party service that may sometimes be unreachable, you might want to implement an exception for the "503 Service Unavailable" HTTP response code. You could do this like so:
from rest_framework.exceptions import APIException
Raised when an incoming request includes incorrect authentication.
By default this exception results in a response with the HTTP status code "401 Unauthenticated", but it may also result in a "403 Forbidden" response, depending on the authentication scheme in use. See the [authentication documentation][authentication] for more details.
## NotAuthenticated
**Signature:** `NotAuthenticated(detail=None)`
Raised when an unauthenticated request fails the permission checks.
By default this exception results in a response with the HTTP status code "401 Unauthenticated", but it may also result in a "403 Forbidden" response, depending on the authentication scheme in use. See the [authentication documentation][authentication] for more details.
The `ValidationError` exception is slightly different from the other `APIException` classes:
* The `detail` argument is mandatory, not optional.
* The `detail` argument may be a list or dictionary of error details, and may also be a nested data structure.
* By convention you should import the serializers module and use a fully qualified `ValidationError` style, in order to differentiate it from Django's built-in validation error. For example. `raise serializers.ValidationError('This field must be an integer value.')`
The `ValidationError` class should be used for serializer and field validation, and by validator classes. It is also raised when calling `serializer.is_valid` with the `raise_exception` keyword argument:
serializer.is_valid(raise_exception=True)
The generic views use the `raise_exception=True` flag, which means that you can override the style of validation error responses globally in your API. To do so, use a custom exception handler, as described above.
By default this exception results in a response with the HTTP status code "400 Bad Request".
