I have the following custom exception handler in Django REST framework.
class ErrorMessage:
def __init__(self, message):
self.message = message
def insta_exception_handler(exc, context):
response = {}
if isinstance(exc, ValidationError):
response['success'] = False
response['data'] = ErrorMessage("Validation error")
return Response(response)
I want a JSON output as shown below
"success":false,
"data":{ "message" : "Validation error" }
But I get the error TypeError: Object of type 'ErrorMessage' is not JSON serializable. Why is a class as simple as ErrorMessage above not JSON serializable? How can I solve this problem?
It is not serializable because it is an object, it should be dict, list or plain value. But you can easily fix your problem by using magic property __dict__
def insta_exception_handler(exc, context):
response = {}
if isinstance(exc, ValidationError):
response['success'] = False
# like this
response['data'] = ErrorMessage("Validation error").__dict__
return Response(response)
I think more generic way would be to create a serializer for serializing the error message object:
from rest_framework import serializers
class ErrorMessageSerializer(serializers.Serializer):
message = serializers.CharField(max_length=256)
Then you can do:
def insta_exception_handler(exc, context):
...
serializer = ErrorMessageSerializer(ErrorMessage("Validation error"))
response["data"] = serializer.data
...
Related
I want to be able to query my mongo db and get the results for all entries in my stocksCollection collection. I am using allStocks = list(stocksCollection.find({})) which gives me a list of all the entries in that collection. However, when I try to return this as the response to a get request, I get the error:
TypeError: The view function did not return a valid response.
The return type must be a string, dict, tuple, Response instance, or WSGI callable, but it was a list.
Here is the simple code I used to get this:
#app.route("/stocks", methods=['GET'])
def getAllStocks():
return list(stocksCollection.find({}))
I have also tried: return stocksCollection.find({}) (errors because it is a type: cursor) and
allStocks = list(stocksCollection.find({}))
return {'data': allStocks}
But that just gives me the error TypeError: Object of type ObjectId is not JSON serializable. Any ideas on what formatt I can change this cursor to so that I am able to return it to my api call (this will not be serving up directly to a webpage, just being called by the frontend to do some calculations)
Create a JSONEncoder class to make ObjectId JSON serializable
import json
from bson import ObjectId
class JSONEncoder(json.JSONEncoder):
def default(self, o):
if isinstance(o, ObjectId):
return str(o)
return json.JSONEncoder.default(self, o)
And then use JSONEncoder class as below (in json.dumps) and make the _id value JSON serializable and append the data into a new list return it.
#app.route("/stocks", methods=['GET'])
def getAllStocks():
output = []
all_data = stocksCollection.find({})
for data in all_data:
data['_id'] = json.dumps(data['_id'], cls=JSONEncoder)
output.appned(data)
return {"data": output}
I think this will solve your problem.
How to access the field value before serialization in my serializer (serializers.Serializer) or rest view (UpdateAPIView)?
I have something like this:
class MySerializer(serializers.Serializer):
my_field = serializers.IntegerField()
If I try to fill my field with 'test' string, it will immediately raise the ValidationError telling me about wrong data type (expecting an integer number of course). Before that error raise, I want to capture the value and do something with it but I have no idea how and where can I access it. It has an empty string value everywhere. I tried to get it in is_valid() before call super() or with raise_exception=False, but I still can not see it:
'_kwargs': {'context': {'format': None,
'request': <rest_framework.request.Request object>,
'view': <rest.views.MyUpdateAPIView object>},
'data': <QueryDict: {'my_field': ['']}>,
'initial_data': <QueryDict: {'my_field': ['']}>,
When I try to find it in my view I can also see nothing:
serializer.initial_data
<QueryDict: {'my_field': ['']}>
request.data
<QueryDict: {'my_field': ['']}>
When I try to check validate() or validate_my_field() methods, I can not even get there because of the ValidationError I mentioned above.
How the serializer validation actually works? What is the order in it and how can I access data before it is "cleaned"?
You can use the .to_internal_value() method to get the data.
https://www.django-rest-framework.org/api-guide/serializers/#overriding-serialization-and-deserialization-behavior
Code exmaple:
def to_representation(self, instance):
ret = super().to_representation(instance)
print(ret['my_field'])
return ret
if you want to access the data you need to get it from the request. Data sent to the api backend can be accessed in the request object.
Example in your view
class MyFieldView(APIView):
def create(self, request, *args, **kwargs):
test_string = request.data['test'] # the name of the item sent to the api
serializer = self.get_serializer(data=request.data)
....
so what you need is request.data
You can override de init method of the serializer and change de data object.
def __init__(self, instance=None, data=empty, **kwargs):
self.instance = instance
if data is not empty:
self.initial_data = data
self.partial = kwargs.pop('partial', False)
self._context = kwargs.pop('context', {})
kwargs.pop('many', None)
super(BaseSerializer, self).__init__(**kwargs)
Have you tried extending error handler?
have a look at this:
https://www.django-rest-framework.org/api-guide/exceptions/
you can get the data and, for example, log it.
If you are only concerned about that field you should try a specific field validator and have it return what you want as it raises the error.
def validate_my_field(self, value) -> int:
if type(value) is int:
return value
raise ValidationError(f"The field entry {value} was not of type int but was {type(value)}")
As per the flask-restful doc, it calls handle_error() function on any 400 or 500 error that happens on a Flask-RESTful route. So I tried to handle exceptions through out my application using this call back, thinking it would leverage multiple try catch block in my application. But while raising custom exception(ResourceNotFound) from a model raises another exception TypeError: Object of type ResourceNotFound is not JSON serializable
from werkzeug.exceptions import HTTPException
from flask_restful import Api
class ExtendedAPI(Api):
def handle_error(self, err):
"""
This class overrides 'handle_error' method of 'Api' class ,
to extend global exception handing functionality of 'flask-restful'
and helps preventing writing unnecessary
try/except block though out the application
"""
# import pdb; pdb.set_trace()
logger.error(err)
# Handle HTTPExceptions
if isinstance(err, HTTPException):
return jsonify({
'message': getattr(
err, 'description', HTTP_STATUS_CODES.get(err.code, '')
)
}), err.code
if isinstance(err, ValidationError):
resp = {
'success': False,
'errors': err.messages
}
return jsonify(resp), 400
# 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
Custom exception:
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 ResourceNotFound(Error):
"""Should be raised in case any resource is not found in the DB"""
The handle_error function handles HTTPException, marshmallow validation errors and the last statement to handle my custom exceptions.
but using pdb, I saw the err object received by handle_error() differs from the custom exception I raised from the model. Not able to figure out any solution for this. Any thoughts on solving this problem or any different approach I can follow??
having trouble serializer a string during a try/except statement.
here i have a endpoint that calls another function refund the response i get back from that function i'm trying to serialize.
class RefundOrder(APIView):
def post(self, request, **kwargs):
print('test')
body_unicode = request.body.decode('utf-8')
body_data = json.loads(body_unicode)
amount = body_data['amount']
tenant = get_object_or_404(Tenant, pk=kwargs['tenant_id'])
refund = SquareGateway(tenant).refund(amount)
serializer = RefundSerializer(refund)
return Response(serializer.data)
this is the function that gets called in the post endpoint. i added it in a try statement to handle the errors from square api. if the api call fails, i want to return an error if their is one, else serialize that data.
def refund(self, order, amount, reason):
try:
response = self.client.transaction().create_refund(stuff)
refund = Refund(
order=order,
amount=response.refund.amount_money.amount,
)
refund.save()
return refund
except ApiException as e:
return json.loads(e.body)['errors'][0]['detail']
this is the the Refundserialize
class RefundSerializer(serializers.ModelSerializer):
class Meta:
model = Refund
fields = ('id', 'amount')
serializing the string doesn't throw an error it just doesn't return the error message that im returning.Currently it returns a empty serialized object.
As far as I understood, You need a custom API exception which returns a custom message.
So, Initially create a custom exception class as below,
from rest_framework.exceptions import APIException
from rest_framework import status
class GenericAPIException(APIException):
"""
raises API exceptions with custom messages and custom status codes
"""
status_code = status.HTTP_400_BAD_REQUEST
default_code = 'error'
def __init__(self, detail, status_code=None):
self.detail = detail
if status_code is not None:
self.status_code = status_code
Then raise the exception in refund() function.
def refund(self, order, amount, reason):
try:
# your code
except ApiException as e:
raise GenericAPIException({"message":"my custom msg"})
I want to define custom error handling for a Flask-restful API.
The suggested approach in the documentation here is to do the following:
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)
Now I find this format pretty attractive but I need to specify more parameters when some exception happens. For example, when encountering ResourceDoesNotExist, I want to specify what id does not exist.
Currently, I'm doing the following:
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))
When called with an id that doesn't exist MyResource will return the following JSON:
{'message': 'ResourceDoesNotExist: Resource MyModel 5 not found'}
This works fine but I'd like to use to Flask-restful error handling instead.
According to the docs
Flask-RESTful will call the handle_error() function on any 400 or 500 error that happens on a Flask-RESTful route, and leave other routes alone.
You can leverage this to implement the required functionality. The only downside is having to create a custom Api.
class CustomApi(flask_restful.Api):
def handle_error(self, e):
flask_restful.abort(e.code, str(e))
If you keep your defined exceptions, when an exception occurs, you'll get the same behaviour as
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))
Instead of attaching errors dict to Api, I am overriding handle_error method of Api class to handle exceptions of my application.
# 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')
Custom exceptions can be kept in separate file, like:
# 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"""
And in the views exceptions can be raised like:
# 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
)
Like in view, exceptions can actually be raised from any file in the app which will be handled by the ExtendedAPI handle_error method.
I've used the Blueprint to work with the flask-restful, and I've found that the solution #billmccord and #cedmt provided on the issue not worked for this case, because the Blueprint don't have the handle_exception and handle_user_exception functions.
My workaround is that enhance the function handle_error of the Api, if the "error handler" of the "Exception" have been registered, just raise it, the "error handler" registered on app will deal with that Exception, or the Exception will be passed to the "flask-restful" controlled "custom error handler".
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)
BTW, seems the flask-restful had been deprecated...
I faced the same issue too and after extending flask-restful.Api I realized that
you really don't need to extend the flask-restful.Api
you can easily do this by inheriting from werkzeug.exceptions.HTTPException and solve this issue
app = Flask(__name__)
api = flask_restful.Api(app)
from werkzeug.exceptions import HTTPException
class APIException(HTTPException):
def __init__(self, code, message):
super().__init__()
self.code = code
self.description = 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().__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))