DRF Exception Handle

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 2021/06/17 

框架报错源码解析

exception 处理器

# rest_framework.views 71-101
def exception_handler(exc, context):
    """
    Returns the response that should be used for any given exception.

    By default we handle the REST framework `APIException`, and also
    Django's built-in `Http404` and `PermissionDenied` exceptions.

    Any unhandled exceptions may return `None`, which will cause a 500 error
    to be raised.
    """
    if isinstance(exc, Http404):
        exc = exceptions.NotFound()
    elif isinstance(exc, PermissionDenied):
        exc = exceptions.PermissionDenied()

    if isinstance(exc, exceptions.APIException):
        headers = {}
        if getattr(exc, 'auth_header', None):
            headers['WWW-Authenticate'] = exc.auth_header
        if getattr(exc, 'wait', None):
            headers['Retry-After'] = '%d' % exc.wait

        if isinstance(exc.detail, (list, dict)):
            data = exc.detail
        else:
            data = {'detail': exc.detail}

        set_rollback()
        return Response(data, status=exc.status_code, headers=headers)

    return None

从处理器源码可以看到，当抛出一个str的错误的时候，处理器会主动为其添加一个detail的key来包裹成可以被后续处理为json的格式，而对于list与dict的格式，则直接返回。

ValidationError 处理

#rest_framework.exceptions.ValidationError 140-158
class ValidationError(APIException):
    status_code = status.HTTP_400_BAD_REQUEST
    default_detail = _('Invalid input.')
    default_code = 'invalid'

    def __init__(self, detail=None, code=None):
        if detail is None:
            detail = self.default_detail
        if code is None:
            code = self.default_code

        # For validation failures, we may collect many errors together,
        # so the details should always be coerced to a list if not already.
        if isinstance(detail, tuple):
            detail = list(detail)
        elif not isinstance(detail, dict) and not isinstance(detail, list):
            detail = [detail]

        self.detail = _get_error_details(detail, code)

对于ValidationError错误，会强制将最后的值转换为list类型，这是考虑到一个field可能有多条不同的错误需要累积。

序列化报错处理

#rest_framework.serializers 323-346
def as_serializer_error(exc):
    assert isinstance(exc, (ValidationError, DjangoValidationError))

    if isinstance(exc, DjangoValidationError):
        detail = get_error_detail(exc)
    else:
        detail = exc.detail

    if isinstance(detail, Mapping):
        # If errors may be a dict we use the standard {key: list of values}.
        # Here we ensure that all the values are *lists* of errors.
        return {
            key: value if isinstance(value, (list, Mapping)) else [value]
            for key, value in detail.items()
        }
    elif isinstance(detail, list):
        # Errors raised as a list are non-field errors.
        return {
            api_settings.NON_FIELD_ERRORS_KEY: detail
        }
    # Errors raised as a string are non-field errors.
    return {
        api_settings.NON_FIELD_ERRORS_KEY: [detail]
    }

drf中的序列化器serializers，在运行run_validation序列化报错的过程中，会给没有列出具体字段错误的detail信息，即不是dict格式的信息，带上一个non_field_errors的key来标准化。

DRF Exception Handle

框架报错源码解析

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