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Union type cannot resolve Object Type at Runtime

I am setting up a GraphQL Server with Python using Starlette and Graphene and ran into a problem I cannot find a solution for. The Graphene Documentation does not go into detail regarding the union type, which I am trying to implement.
I set up a minimum example based on the graphene documentation which you can run to replicate this problem
import os
import uvicorn
from graphene import ObjectType, Field, List, String, Int, Union
from graphene import Schema
from starlette.applications import Starlette
from starlette.graphql import GraphQLApp
from starlette.routing import Route
mock_data = {
"episode": 3,
"characters": [
{
"type": "Droid",
"name": "R2-D2",
"primaryFunction": "Astromech"
},
{
"type": "Human",
"name": "Luke Skywalker",
"homePlanet": "Tatooine"
},
{
"type": "Starship",
"name": "Millennium Falcon",
"length": 35
}
]
}
class Human(ObjectType):
name = String()
homePlanet = String()
class Droid(ObjectType):
name = String()
primary_function = String()
class Starship(ObjectType):
name = String()
length = Int()
class Characters(Union):
class Meta:
types = (Human, Droid, Starship)
class SearchResult(ObjectType):
characters = List(Characters)
episode = Int()
class RootQuery(ObjectType):
result = Field(SearchResult)
#staticmethod
def resolve_result(_, info):
return mock_data
graphql_app = GraphQLApp(schema=Schema(query=RootQuery))
routes = [
Route("/graphql", graphql_app),
]
api = Starlette(routes=routes)
if __name__ == "__main__":
uvicorn.run(api, host="127.0.0.1", port=int(os.environ.get("PORT", 8080)))
If you then go to http://localhost:8080/graphq and enter the following query
query Humans{
result {
episode
characters {
... on Human {
name
}
}
}
}
I get this error
{
"data": {
"result": {
"episode": 3,
"characters": null
}
},
"errors": [
{
"message": "Abstract type Characters must resolve to an Object type at runtime for field SearchResult.characters with value \"[{'type': 'Droid', 'name': 'R2-D2', 'primaryFunction': 'Astromech'}, {'type': 'Human', 'name': 'Luke Skywalker', 'homePlanet': 'Tatooine'}, {'type': 'Starship', 'name': 'Millennium Falcon', 'length': 35}]\", received \"None\".",
"locations": [
{
"line": 4,
"column": 5
}
]
}
]
}
which I am now stuck with. Maybe someone has done this already and can help out? How can I resolve this at runtime. I have already tried different approaches for example I changed classes Character and RootQuery:
class Character(Union):
class Meta:
types = (Human, Droid, Starship)
def __init__(self, data, *args, **kwargs):
super().__init__(*args, **kwargs)
self.data = data
self.type = data.get("type")
def resolve_type(self, info):
if self.type == "Human":
return Human
if self.type == "Droid":
return Droid
if self.type == "Starship":
return Starship
class RootQuery(ObjectType):
result = Field(SearchResult)
#staticmethod
def resolve_result(_, info):
return {**mock_data, "characters": [Character(character) for character in mock_data.get('characters')]}
resulting in
{
"data": {
"result": {
"episode": 3,
"characters": [
{},
{
"name": null
},
{}
]
}
}
}
Any ideas would be very appreciated!

jkimbo answered the question here:
class Character(Union):
class Meta:
types = (Human, Droid, Starship)
#classmethod
def resolve_type(cls, instance, info):
if instance["type"] == "Human":
return Human
if instance["type"] == "Droid":
return Droid
if instance["type"] == "Starship":
return Starship
class RootQuery(ObjectType):
result = Field(SearchResult)
def resolve_result(_, info):
return mock_data
Note I'm just returning mock_data and I've updated the resolve_type method to switch based on the data. The Union type uses the same resolve_type method as Interface to figure out what type to resolve to at runtime: https://docs.graphene-python.org/en/latest/types/interfaces/#resolving-data-objects-to-types

Django rest - convert field into a list?

I have a Textfield in my model which stores dictionaries, I would like to convert this field into a dictionary if possible in a rest serializer.
at the moment the field returns the dictionary but backslashes all the quotes, it is possible to convert the strings into a nested list of dicts?
Thanks
api currently returns below:
{
"id": 3,
"hostname": "WAN-EDGE",
"timestamp": "2019-04-12T11:34:36.654521",
"routing_table": "[{\"route\": \"0.0.0.0\", \"subnet_mask\": \"0.0.0.0\", \"next_hop\": \"172.16.66.193\"}, {\"route\": \"10.10.21.0\", \"subnet_mask\": \"255.255.255.0\", \"next_hop\": \"172.16.67.146\"}, {\"route\": \"10.22.0.0\", \"subnet_mask\": \"255.255.0.0\", \"next_hop\": \"172.18.1.5\"}, {\"route\": \"10.31.0.0\", \"subnet_mask\": \"255.255.0.0\", \"next_hop\": \"172.16.67.146\"},...]"
},...
}
desired result a nested list of dicts
{
"id": 3,
"hostname": "WAN-EDGE",
"timestamp": "2019-04-12T11:34:36.654521",
"routing_table": [
{
"route": "0.0.0.0",
"subnet_mask": "0.0.0.0",
"next_hop": "172.16.66.193"
},
{
"route": "10.10.21.0",
"subnet_mask": "255.255.255.0",
"next_hop": "172.16.67.146"
},
{
"route": "10.22.0.0",
"subnet_mask": "255.255.0.0",
"next_hop": "172.18.1.5"
},
{
"route": "10.31.0.0",
"subnet_mask": "255.255.0.0",
"next_hop": "172.16.67.146"
},...
]
},...
}
Current serialiser:
class RoutingTableSerializer(serializers.ModelSerializer):
hostname = serializers.ReadOnlyField(
source='device.hostname',
)
rt = serializers.JSONField(
source='routing_table'
)
class Meta:
model = DeviceData
fields = ('id','hostname','timestamp','rt')

You may need serializers.JSONField()
Update-1
You could also try with SerializerMethodField() as
import json
class RoutingTableSerializer(serializers.ModelSerializer):
hostname = serializers.ReadOnlyField(source='device.hostname', )
rt = serializers.SerializerMethodField(source='routing_table', read_only=True)
def get_routing_table(self, instance):
return json.loads(instance.routing_table)
class Meta:
model = DeviceData
fields = ('id', 'hostname', 'timestamp', 'rt')

post request for lis of items using python flask

I am trying to do post request for below schema using flask-mongoAlchemy
class Sensors(db.Document):
sensorName = db.StringField()
sensorStatus = db.StringField()
class Camera(db.Document):
cameraName = db.StringField()
cameraStatus = db.StringField()
class Checkpoints(db.Document):
checkPointName = db.StringField()
class Gateway(db.Document):
sensors = db.ListField(db.DocumentField(Sensors), db_field='sensors')
camera = db.ListField(db.DocumentField(Camera), db_field='camera')
checkpoints = db.ListField(db.DocumentField(Checkpoints), db_field='checkpoints')
In the schema Gateway class contains the list of other three classes
Tried doing as shown below
#gateway_bp.route('/gateway',methods=['POST'])
def object_book():
request_data = request.get_json()
sensorsList=[]
cameraList=[]
checkList=[]
for sensorObj in request_data['GateWay1']['sensors']:
sensorsList.append(Sensors(sensorName=sensorObj['sensorName'],sensorStatus=sensorObj['sensorStatus']))
gatewayObj=Gateway(sensors=sensorsList)
for cameraObj in request_data['GateWay1']['camera']:
cameraList.append(Camera(cameraName=cameraObj['cameraName'],cameraStatus=cameraObj['cameraStatus']))
gatewayObj=Gateway(camera=cameraList)
for checkListObj in request_data['GateWay1']['checkpoints']:
checkList.append(Checkpoints(checkPointName=checkListObj['checkPointName']))
gatewayObj=Gateway(checkpoints=checkList)
gatewayObj.save()
return 'Saved :)'
getting the error has
mongoalchemy.exceptions.MissingValueException
MissingValueException: sensors
sample payload
{
"GateWay1": {
"sensors": [{
"sensorName": "s1",
"sensorStatus": "green "
}, {
"sensorName": "s2",
"sensorStatus": "red "
}],
"camera": [{
"cameraName": "cam1",
"cameraStatus": "live"
}, {
"cameraName": "cam2",
"cameraStatus": "live"
}],
"checkpoints": [{
"checkPointName": "chk1"
}, {
"checkPointName": "chk2"
}]
}
}
please help in saving the above json in mongodb using mongoAlchemy ,please point some sample repo where i can know more about flask-mongoAlchemy

Projection using MongoEngine Raw-Query

Does anyone know, how I can implement the following MongoDB query using a MongoEngine Raq-Query?
db.getCollection('subscribers').find({
'_id': ObjectId("579e60b0c525fd2037e8dd31"),
'history.content.read_process_msg': {
'$exists':true
},
'history.content.read_processed': {
'$exists':true
},
'history.content.read_processed': false
},
{'history.$':1})
I read, that the raw-query doesn't support projections and that one should use .only() instead. But the problem here is, that it returns all the empty documents also…
Any advice?
Edit: Here are my models and a sample document:
class Subscriber(Document):
service = StringField()
history = EmbeddedDocumentListField('SubscriberHistory')
def __str__(self):
return self.service
class SubscriberHistory(EmbeddedDocument):
action = StringField()
content = DictField()
def __str__(self):
return self.action
And the sample:
{
"_id" : ObjectId("579e60b0c525fd2037e8dd31"),
"service" : "foo",
"history" : [
{
"action" : "outbound",
"content" : {
"read_processed" : false,
"message_data" : {
"text" : "w00t?"
},
"read_process_msg" : {
"$ref" : "bots_messages",
"$id" : ObjectId("57a6529dc525fd8066ee25b3")
}
},
"created_at" : ISODate("2016-08-06T21:12:00.986Z")
}
]
}

Flask-restful: marshal complex object to json

I have a question regarding flask restful extension. I'm just started to use it and faced one problem. I have flask-sqlalchemy entities that are connected many-to-one relation and I want that restful endpoint return parent entity with all its children in json using marshaller. In my case Set contains many parameters. I looked at flask-restful docs but there wasn't any explanation how to solve this case.
Seems like I'm missing something obvious but cannot figure out any solution.
Here is my code:
# entities
class Set(db.Model):
id = db.Column("id", db.Integer, db.Sequence("set_id_seq"), primary_key=True)
title = db.Column("title", db.String(256))
parameters = db.relationship("Parameters", backref="set", cascade="all")
class Parameters(db.Model):
id = db.Column("id", db.Integer, db.Sequence("parameter_id_seq"), primary_key=True)
flag = db.Column("flag", db.String(256))
value = db.Column("value", db.String(256))
set_id = db.Column("set_id", db.Integer, db.ForeignKey("set.id"))
# marshallers
from flask.ext.restful import fields
parameter_marshaller = {
"flag": fields.String,
"value": fields.String
}
set_marshaller = {
'id': fields.String,
'title': fields.String,
'parameters': fields.List(fields.Nested(parameter_marshaller))
}
# endpoint
class SetApi(Resource):
#marshal_with(marshallers.set_marshaller)
def get(self, set_id):
entity = Set.query.get(set_id)
return entity
restful_api = Api(app)
restful_api.add_resource(SetApi, "/api/set/<int:set_id>")
Now when i call /api/set/1 I get server error:
TypeError: 'Set' object is unsubscriptable
So I need a way to correctly define set_marshaller that endpoint return this json:
{
"id": : "1",
"title": "any-title",
"parameters": [
{"flag": "any-flag", "value": "any-value" },
{"flag": "any-flag", "value": "any-value" },
.....
]
}
I appreciate any help.

I found solution to that problem myself.
After playing around with flask-restful i find out that i made few mistakes:
Firstly set_marshaller should look like this:
set_marshaller = {
'id': fields.String,
'title': fields.String,
'parameters': fields.Nested(parameter_marshaller)
}
Restless marshaller can handle case if parameter is list and marshals to json list.
Another problem was that in API Set parameters has lazy loading, so when i try to marshall Set i got KeyError: 'parameters', so I need explicitly load parameters like this:
class SetApi(Resource):
#marshal_with(marshallers.set_marshaller)
def get(self, set_id):
entity = Set.query.get(set_id)
entity.parameters # loads parameters from db
return entity
Or another option is to change model relationship:
parameters = db.relationship("Parameters", backref="set", cascade="all" lazy="joined")

This is an addition to Zygimantas's answer:
I'm using Flask-RESTful and this is a solution to the loading of the nested properties.
You can pass a callable to the marshal decorator:
class OrgsController(Resource):
#marshal_with(Organization.__json__())
def get(self):
return g.user.member.orgs
Then update the models to return the resource fields for its own entity. Nested entities will thus return the resource fields for its entity relatively.
class Organization(db.Model):
id = db.Column(db.Integer, primary_key=True)
...
#staticmethod
def __json__(group=None):
_json = {
'id': fields.String,
'login': fields.String,
'description': fields.String,
'avatar_url': fields.String,
'paid': fields.Boolean,
}
if group == 'flat':
return _json
from app.models import Repository
_json['repos'] = fields.Nested(Repository.__json__('flat'))
return _json
class Repository(db.Model):
id = db.Column(db.Integer, primary_key=True)
owner_id = db.Column(db.Integer, db.ForeignKey('organization.id'))
owner = db.relationship('Organization', lazy='select', backref=db.backref('repos', lazy='select'), foreign_keys=[owner_id])
...
#staticmethod
def __json__(group=None):
_json = {
'id': fields.String,
'name': fields.String,
'updated_at': fields.DateTime(dt_format='iso8601'),
}
if group == 'flat':
return _json
from app.models import Organization
_json['owner'] = fields.Nested(Organization.__json__('flat'))
return _json
This gives the representation I'm looking for, and honoring the lazy loading:
[
{
"avatar_url": "https://avatars.githubusercontent.com/u/18945?v=3",
"description": "lorem ipsum.",
"id": "1805",
"login": "foobar",
"paid": false,
"repos":
[
{
"id": "9813",
"name": "barbaz",
"updated_at": "2014-01-23T13:51:30"
},
{
"id": "12860",
"name": "bazbar",
"updated_at": "2015-04-17T11:06:36"
}
]
}
]
I like
1) how this approach allows me to define my resource fields per entity and it is available to all my resource routes across the app.
2) how the group argument allows me to customise the representation however I desire. I only have 'flat' here, but any logic can be written and passed down to deeper nested objects.
3) entities are only loaded as necessary.