[Bug] Batching throws error when Flask auto-reload is enabled

[ericaiq]

Hi,

I'm currently upgrading a graphene 2 project to graphene 3. The project uses graphene-sqlalchemy and graphql-server[flask]. I'm noticing strange behavior when using batching while flask is in development mode, specifically when auto-reload is enabled. When auto-reload is enabled and batching is enabled, then all requests fail. Instead an asyncio error is thrown, TypeError: UserConvo fields cannot be resolved. There is no current event loop in thread 'Thread-1'. The issue only occurs when batching is enabled and flask auto reload is enabled. Disabling batching or disabling the flask auto-reload resolves the issue. The issue also only occurs with a many to many relationship that include the back_populates param in the relationships.

Below is a [somewhat] minimal example to reproduce the issue. The app.py, schema.py, and requirements.txt file are below.

Let me know if you need more info or clarification. Thanks!

Repro:
0) set up a virtual env and install packages from requirements.txt below. Then copy app.py and schema.py to your working directory.

1. run: FLASK_ENV=development && flask run
2. execute query { __schema { types { name } } } and receive error TypeError: UserConvo fields cannot be resolved. There is no current event loop in thread 'Thread-1'.
3. run `FLASK_ENV=development && flask run --no-reload
4. execute query { __schema { types { name } } } and receive no error.

Error Trace:

Traceback (most recent call last):
  File "/Users/erichemphill/workspace/craft/graphene-test/app.py", line 4, in <module>
    from schema import schema
  File "/Users/erichemphill/workspace/craft/graphene-test/schema.py", line 74, in <module>
    schema = Schema(query=Query)
  File "/Users/erichemphill/workspace/craft/graphene-test/env/lib/python3.8/site-packages/graphene/types/schema.py", line 430, in __init__
    self.graphql_schema = GraphQLSchema(
  File "/Users/erichemphill/workspace/craft/graphene-test/env/lib/python3.8/site-packages/graphql/type/schema.py", line 208, in __init__
    collect_referenced_types(query)
  File "/Users/erichemphill/workspace/craft/graphene-test/env/lib/python3.8/site-packages/graphql/type/schema.py", line 423, in collect_referenced_types
    collect_referenced_types(field.type)
  File "/Users/erichemphill/workspace/craft/graphene-test/env/lib/python3.8/site-packages/graphql/type/schema.py", line 422, in collect_referenced_types
    for field in named_type.fields.values():
  File "/opt/homebrew/Cellar/python@3.8/3.8.12_1/Frameworks/Python.framework/Versions/3.8/lib/python3.8/functools.py", line 967, in __get__
    val = self.func(instance)
  File "/Users/erichemphill/workspace/craft/graphene-test/env/lib/python3.8/site-packages/graphql/type/definition.py", line 737, in fields
    raise TypeError(f"{self.name} fields cannot be resolved. {error}")
TypeError: UserConvo fields cannot be resolved. There is no current event loop in thread 'Thread-1'.

schema.py:

from graphene import Field, ObjectType, Schema
from graphene import relay
from graphene_sqlalchemy import SQLAlchemyObjectType
from sqlalchemy.orm import declarative_base, relationship
from sqlalchemy import Column, Integer, ForeignKey, BigInteger

Base = declarative_base()

class UserModel(Base):  # pylint: disable=too-few-public-methods
    """
    Models the User Object
    """

    __tablename__ = "user"
    user_id = Column(BigInteger, primary_key=True, autoincrement=True)
    convos = relationship("UserConvoAssociation", back_populates="user")

class UserConvoAssociation(Base):
    """
    Association Object for User and Convo relationships
    """

    __tablename__ = "user_convo"
    convo_id = Column(ForeignKey("convo.convo_id"), primary_key=True)
    user_id = Column(ForeignKey("user.user_id"), primary_key=True)
    num_unread_messages = Column(Integer, default=0)

    convo = relationship("ConvoModel", back_populates="users")
    user = relationship("UserModel", back_populates="convos")
    
class ConvoModel(Base):  # pylint: disable=too-few-public-methods
    """
    Models the Convo object
    """

    __tablename__ = "convo"
    convo_id = Column(BigInteger, primary_key=True, autoincrement=True)
    users = relationship("UserConvoAssociation", back_populates="convo")


class UserConvo(SQLAlchemyObjectType):
    """
    User x Convo relationship
    """

    class Meta:
        model = UserConvoAssociation
        interfaces = (relay.Node,)
        batching = True


class User(SQLAlchemyObjectType):
    """
    Defines the schema for a User
    """

    class Meta:
        """
        Defines the metadata for a User
        """

        model = UserModel
        interfaces = (relay.Node,)
        batching = True


class Query(ObjectType):
    convo = Field(UserConvo)
    user = Field(User)

schema = Schema(query=Query)

app.py

from flask import Flask
from graphql_server.flask import GraphQLView

from schema import schema

app = Flask(__name__)

app.add_url_rule('/graphql', view_func=GraphQLView.as_view(
    'graphql',
    schema=schema.graphql_schema,
    graphiql=True,
))

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

requirements.txt (this is not a minimal requirements.txt. it's from the project that i'm working on.)

aiodataloader==0.2.1
aiohttp==4.0.0a1
alembic==1.7.6
aniso8601==9.0.1
asgiref==3.5.0
async-timeout==3.0.1
attrs==21.4.0
aws-embedded-metrics==1.0.7
bcrypt==3.2.0
boto3==1.21.1
botocore==1.24.1
certifi==2021.10.8
cffi==1.15.0
cfn-flip==1.3.0
chardet==3.0.4
charset-normalizer==2.0.12
click==8.0.3
exponent-server-sdk==2.0.0
Flask==2.0.3
Flask-Migrate==3.1.0
Flask-SQLAlchemy==2.5.1
graphene==3.0
graphene-sqlalchemy==3.0.0b1
graphql-core==3.1.7
graphql-relay==3.1.5
graphql-server==3.0.0b4
idna==3.3
importlib-metadata==4.11.1
importlib-resources==5.4.0
itsdangerous==2.0.1
Jinja2==3.0.3
jmespath==0.10.0
Mako==1.1.6
MarkupSafe==2.0.1
multidict==4.7.6
phonenumbers==8.12.43
promise==2.3
psycopg2==2.9.3
pycparser==2.21
python-dateutil==2.8.2
python-http-client==3.3.6
PyYAML==5.3.1
requests==2.27.1
s3transfer==0.5.1
sendgrid==6.9.6
six==1.16.0
SQLAlchemy==1.4.31
starkbank-ecdsa==2.0.3
troposphere==3.2.2
typing-extensions==3.10.0.2
urllib3==1.26.8
Werkzeug==2.0.3
yarl==1.7.2
zipp==3.7.0

[erikwrede]

This looks like an issue with graphql-server[flask] or graphene rather than this library. Maybe the event loop introduced with graphene3 is destroyed during live-reload?
Have you found any fix so far?

[ericaiq]

Unfortunately I did not find a solution outside of disabling the live-reload. The project I was working on actually pivoted away from Graphene so I'm no longer using this library.

[erikwrede]

Thank you for the reply! I'll keep this open for further reference and try to find a solution next time I'm working on something flask-related. Thanks for reporting.