在 Python Flask RestPlus 上捕获异常

Question

I am struggling with finding a way to return a response when a call to one of my APIs does not return any result. I am using flask_restplus, and tried to use the @api.errorhandler annotation with no success and then I resorted to try a plain try/except block in my class.

In this particular issue, I am trying to call the endpoint, where the GUID is a non-existent user in the database.

http://localhost:5000/api/users/b3d8e86b-f2ad-4b6a-b768-e7adc1d94ced

The user end point has been defined as following:

import logging

from flask import Response
from flask_restplus import Resource, fields
from neomodel.core import DoesNotExist

from app.api.restplus import api
from app.models import User

log = logging.getLogger(__name__)

ns = api.namespace('users', description='Users')

user = api.model('user', {
    'id': fields.Integer(readOnly=True, description='The internal id of of a user'),
    'user_id': fields.String(required=True, description='The user unique identifier')}
)

@ns.route('/')
@api.response(404, 'Users not found.')
class UsersList(Resource):

    @api.marshal_list_with(user)
    def get(self):
        """
        Returns a list of all users
        :return: list_of_users
        """
        try:
            users = User.nodes
            list_of_users = list(users)
            return list_of_users
    #        return json.dumps(dict(users = [user.serialize for user in list_of_users]))
        except DoesNotExist:
            return Response(('{"No Content": "No user nodes found"}'), status = 200, mimetype = 'application/json')


@ns.route('/<string:user_id>')
class UserItem(Resource):

   @api.marshal_with(user)
   def get(self, user_id):
        """
        Returns a user with the given user_id
        :param id: user_id
        :return: user
        """
        try:
            user = User.nodes.get(user_id=user_id)
            return user
        except User.DoesNotExist:
            return Response({'message': 'Could not locate a user with the user_id provided.'}, 404)

My initialization is done in app/ init .py:

import logging.config
from flask import Flask, Blueprint
from neomodel import clear_neo4j_database
from neomodel import db

from app.config import Configuration
from app.web_app.routes import webapp_mod
from app.data_loader.routes import dataloader_mod
from app.utilities import prepare_rerun
from app.api.endpoints.users import ns as users_namespace
from app.api.endpoints.sessions import ns as sessions_namespace
from app.api.endpoints.browsers import ns as browsers_namespace
from app.api.endpoints.os import ns as os_namespace
from app.api.endpoints.applications import ns as applications_namespace
from app.api.endpoints.tenants import ns as tenants_namepspace
from app.api.endpoints.devices import  ns as devices_namespace
from app.api.endpoints.environments import ns as environments_namespace

from app.api.restplus import api
from os import path


app = Flask(__name__)
app.config.from_object(Configuration)
app.register_blueprint(dataloader_mod, url_prefix='/data_loader')
log_file_path = path.join(path.dirname(path.abspath(__file__)), 'logging.conf')
logging.config.fileConfig(log_file_path)
log = logging.getLogger(__name__)

blueprint = Blueprint('api', __name__, url_prefix='/api')
api.init_app(blueprint)
api.add_namespace(users_namespace)
api.add_namespace(sessions_namespace)
api.add_namespace(browsers_namespace)
api.add_namespace(applications_namespace)
api.add_namespace(tenants_namepspace)
api.add_namespace(devices_namespace)
api.add_namespace(os_namespace)
api.add_namespace(environments_namespace)

The resplus.py module where I define the api at this point has just the definition of the api object, but I had tried to follow some examples online and define in it methods to handle the exceptions through the annotations in the users object.

from flask_restplus import Api
from neomodel.core import DoesNotExist

api = Api(version='1.0', title='Users Activity Log',
          description='An API to retreive information about users'' activities in Infor Ming.le')

However when I make the call, instead of getting a JSON response with the message and 404 code, I am getting:

{
    "id": null,
    "user_id": null
}

Thanks in advance for any help.

Answer 1

I suppose I am a little late to help you but I might help other people having the same problem:

The thing is, although you have an other return code (and you have an error) flask still tries to use @marshal_with(user) . It might be a little bit confusing at first.

If you look at this answer you can see how to return multiple answer types without loosing the swagger functionality plus you still got the marshalling. This is a bit more versatile than the standard @marshal_with .

There are other ways of achieving similar results for errors: Eg you could use the abort() function (which might be more logical in some cases).

So in other words your code transformed would look somehow like this:

import logging

from flask import Response
from flask_restplus import Resource, fields, marshal
from neomodel.core import DoesNotExist

from app.api.restplus import api
from app.models import User

log = logging.getLogger(__name__)

ns = api.namespace('users', description='Users')

user = api.model('user', {
    'id': fields.Integer(readOnly=True, description='The internal id of of a user'),
    'user_id': fields.String(required=True, description='The user unique identifier')}
)

@ns.route('/')
@api.response(404, 'Users not found.')
class UsersList(Resource):

    @api.response(model=user, code=200)
    @api.response(404, 'Users not found.')
    def get(self):
        """
        Returns a list of all users
        :return: list_of_users
        """
        try:
            users = User.nodes
            list_of_users = list(users)
            return marshal(list_of_users)
        except DoesNotExist:
            return {"No Content": "No user nodes found"}, 404


@ns.route('/<string:user_id>')
class UserItem(Resource):

   @api.response(model=user, code=200)
   @api.response(code=404, 'Users not found.')
   def get(self, user_id):
        """
        Returns a user with the given user_id
        :param id: user_id
        :return: user
        """
        try:
            user = User.nodes.get(user_id=user_id)
            return marshal(user)
        except User.DoesNotExist:
            return {'message': 'Could not locate a user with the user_id provided.'}, 404

# More Endpoints - I hope this did the job...

Answer 2

You can use

from flask_restplus import abort
abort(400, custom='value')

To abort and through errors

or

namespace.abort(400, "An error occured") 

Answer 3

This is likely no longer relevant as your question is from quite a while ago, but I came across this as I was searching around for flask-restplus exception handling best practices. I don't think your problem is with flask-restplus' exception handling. It sounds like your User class is not raising a DoesNotExist exception when the user doesn't exist. Did you verify whether you're even hitting the Except: block?

Anyhow, once you verify that you are indeed raising the DoesNotExist exception, you can register an errorhandler for that exception in your init.py like this:

@api.errorhandler(DoesNotExist)
def handle_user_does_not_exist_error(error):
    return ({'message': 'Could not locate a user with the user_id provided.'}, 404)