"Advanced : Nested Field" doc example is creating set() by mistake

[zarnovican]

The second data structure is actually a valid syntax for set().

user_fields = {
    'id': fields.Integer,
    'name': fields.String,
}

user_list_fields = {
    fields.List(fields.Nested(user_fields)),
}

Looking at the code for marshal(), the function would never work with set. Bombs-out on https://github.com/flask-restful/flask-restful/blob/master/flask_restful/__init__.py#L632

I don't know how to correct the example since this snippet works for me (marshaling list of user objects):

user_fields = {
    'id':       fields.String(attribute='_id'),
    'email':    fields.String,
}

class User(Resource):

    @marshal_with(user_fields)
    def get(self, id):
        return model.get_user(id)

class UserList(Resource):

    @marshal_with(user_fields)
    def get(self):
        return model.users.values()     # returns a list of User() objects

So I guess, better example is needed where Nested with List is really required.

[joshfriend]

Nice catch. It should really be something like:

user_list_fields = {
   'users':  fields.List(fields.Nested(user_fields)),
}

[zarnovican]

It should really be something like..

I don't know. I've played with it for some time. Even with _fields as proper dictionary, marshaling looks weird. Full example:

from flask import Flask
from flask_restful import fields, marshal_with, Api, Resource

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

class MyUser(object):

    def __init__(self, name):
        self.name = name

users = { 'joe': MyUser('joe'), 'jane': MyUser('jane'), }

user_fields = {
    'name':     fields.String,
}

user_list_fields = {
    'users':    fields.List(fields.Nested(user_fields)),
}

class User(Resource):

    @marshal_with(user_fields)
    def get(self, name):
        return users[name]

class UserList(Resource):

    @marshal_with(user_list_fields)
    def get(self):
        return users.values()

api.add_resource(UserList, '/users')
api.add_resource(User,     '/users/<name>', endpoint='user')

if __name__ == '__main__':
    app.run(debug=True)

$ curl localhost:5000/users/jane
{
    "name": "jane"
}
$ curl localhost:5000/users
{
    "users": null
}

My understanding is that marshal() will call itself on every element of the list (if returned data is a list). So it will try to marshal single User() object using user_list_fields.

[joshfriend]

Try this instead?

class UserList(Resource):

    @marshal_with(user_list_fields)
    def get(self):
        return {'users': users.values()}

you would nest the users list inside another object to be able to also return other metadata info with the response, such as pagination info.

[zarnovican]

Thanks! It worked. Though, I had to wrap it in list().

    @marshal_with(user_list_fields)
    def get(self):
        return { 'users': list(users.values()), }

Off-topic: It has to do with Py3's .values(). Code fails inside _get_value_for_key func because indexing on dict_values won't work.

>>> d = {'a': 1, 'b': 2, }
>>> vs = d.values()
>>> vs
dict_values([2, 1])
>>> is_indexable_but_not_string(vs)
True
>>> vs[1]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'dict_values' object does not support indexing
>>>