轻松解决-自定义错误处理

Question

我想为Flask-restful API定义自定义错误处理。

在文档中建议的方法在这里是要做到以下几点：

errors = {
    'UserAlreadyExistsError': {
        'message': "A user with that username already exists.",
        'status': 409,
    },
    'ResourceDoesNotExist': {
        'message': "A resource with that ID no longer exists.",
        'status': 410,
        'extra': "Any extra information you want.",
    },
}
app = Flask(__name__)
api = flask_restful.Api(app, errors=errors)

现在，我发现此格式非常吸引人，但是当发生某些异常时，我需要指定更多参数。例如，遇到时ResourceDoesNotExist，我要指定id不存在的内容。

目前，我正在执行以下操作：

app = Flask(__name__)
api = flask_restful.Api(app)


class APIException(Exception):
    def __init__(self, code, message):
        self._code = code
        self._message = message

    @property
    def code(self):
        return self._code

    @property
    def message(self):
        return self._message

    def __str__(self):
        return self.__class__.__name__ + ': ' + self.message


class ResourceDoesNotExist(APIException):
    """Custom exception when resource is not found."""
    def __init__(self, model_name, id):
        message = 'Resource {} {} not found'.format(model_name.title(), id)
        super(ResourceNotFound, self).__init__(404, message)


class MyResource(Resource):
    def get(self, id):
        try:
            model = MyModel.get(id)
            if not model:
               raise ResourceNotFound(MyModel.__name__, id)
        except APIException as e:
            abort(e.code, str(e))

当使用不存在的ID调用时，MyResource将返回以下JSON：

{'message': 'ResourceDoesNotExist: Resource MyModel 5 not found'}

这工作正常，但我想使用Flask-restful错误处理。

Answer 1

我没有将错误字典附加到 Api，而是覆盖 Api 类的 handle_error 方法来处理我的应用程序的异常。

# File: app.py
# ------------

from flask import Blueprint, jsonify
from flask_restful import Api
from werkzeug.http import HTTP_STATUS_CODES
from werkzeug.exceptions import HTTPException

from view import SomeView

class ExtendedAPI(Api):
    """This class overrides 'handle_error' method of 'Api' class ,
    to extend global exception handing functionality of 'flask-restful'.
    """
    def handle_error(self, err):
        """It helps preventing writing unnecessary
        try/except block though out the application
        """
        print(err) # log every exception raised in the application
        # Handle HTTPExceptions
        if isinstance(err, HTTPException):
            return jsonify({
                    'message': getattr(
                        err, 'description', HTTP_STATUS_CODES.get(err.code, '')
                    )
                }), err.code
        # If msg attribute is not set,
        # consider it as Python core exception and
        # hide sensitive error info from end user
        if not getattr(err, 'message', None):
            return jsonify({
                'message': 'Server has encountered some error'
                }), 500
        # Handle application specific custom exceptions
        return jsonify(**err.kwargs), err.http_status_code


api_bp = Blueprint('api', __name__)
api = ExtendedAPI(api_bp)

# Routes
api.add_resource(SomeView, '/some_list')

自定义异常可以保存在单独的文件中，例如：

# File: errors.py
# ---------------


class Error(Exception):
    """Base class for other exceptions"""
    def __init__(self, http_status_code:int, *args, **kwargs):
        # If the key `msg` is provided, provide the msg string
        # to Exception class in order to display
        # the msg while raising the exception
        self.http_status_code = http_status_code
        self.kwargs = kwargs
        msg = kwargs.get('msg', kwargs.get('message'))
        if msg:
            args = (msg,)
            super().__init__(args)
        self.args = list(args)
        for key in kwargs.keys():
            setattr(self, key, kwargs[key])


class ValidationError(Error):
    """Should be raised in case of custom validations"""

并且在视图中可以引发异常，例如：

# File: view.py
# -------------

from flask_restful import Resource
from errors import ValidationError as VE


class SomeView(Resource):
    def get(self):
        raise VE(
            400, # Http Status code
            msg='some error message', code=SomeCode
        )

与视图一样，实际上可以从应用程序中的任何文件引发异常，这些文件将由 ExtendedAPI handle_error 方法处理。

Answer 2

根据文档

Flask-RESTful将在Flask-RESTful路由上发生的任何400或500错误上调用handle_error（）函数，并且不理会其他路由。

您可以利用它来实现所需的功能。唯一的缺点是必须创建自定义Api。

class CustomApi(flask_restful.Api):

    def handle_error(self, e):
        flask_restful.abort(e.code, str(e))

如果保留定义的异常，则当发生异常时，您将获得与

class MyResource(Resource):
    def get(self, id):
        try:
            model = MyModel.get(id)
            if not model:
               raise ResourceNotFound(MyModel.__name__, id)
        except APIException as e:
            abort(e.code, str(e))

Answer 3

我已经使用蓝图来处理flask-restful，我发现在这个问题上提供的解决方案@billmccord 和@cedmt不适用于这种情况，因为蓝图没有handle_exception和handle_user_exception功能。

我的解决方法是，提高功能handle_error的Api，如果“异常”的“错误处理程序”已被注册，只是提出来，在应用程序注册了“错误处理程序”会处理该异常，或异常将被传递到“flask-restful”控制的“自定义错误处理程序”。

class ImprovedApi(Api):
    def handle_error(self, e):
        for val in current_app.error_handler_spec.values():
            for handler in val.values():
                registered_error_handlers = list(filter(lambda x: isinstance(e, x), handler.keys()))
                if len(registered_error_handlers) > 0:
                    raise e
        return super().handle_error(e)


api_entry = ImprovedApi(api_entry_bp)

顺便说一句，似乎flask-restful已被弃用......