SQLAlchemyObjectType hides original SQLAlchemy exception

[Fedalto]

Hi all!

Here's a minimal code that explains the issue.

import graphene
from graphene_sqlalchemy import SQLAlchemyObjectType
from sqlalchemy import Column, Integer
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship

Base = declarative_base()


class A(Base):
    __tablename__ = 'a'
    id = Column(Integer, primary_key=True)


class B(Base):
    __tablename__ = 'b'
    id = Column(Integer, primary_key=True)

    a = relationship(A)  # This is the breaking line


class BSchema(SQLAlchemyObjectType):
    class Meta:
        model = B


schema = graphene.Schema(query=BSchema)

When I try to run this file I only get this error:

Traceback (most recent call last):
  File "issue.py", line 22, in <module>
    class BSchema(SQLAlchemyObjectType):
  File "./.venv/lib/python3.6/site-packages/graphene/utils/subclass_with_meta.py", line 40, in __init_subclass__
    super_class.__init_subclass_with_meta__(**options)
  File "./.venv/src/graphene-sqlalchemy/graphene_sqlalchemy/types.py", line 97, in __init_subclass_with_meta__
    ).format(cls.__name__, model)
AssertionError: You need to pass a valid SQLAlchemy Model in BSchema.Meta, received "<class '__main__.B'>".

But I'm passing a valid SQLAlchemy Model in BSchema.Meta.

The problem is actually another.
SQLAlchemy is raising this exception:
{NoForeignKeysError}Could not determine join condition between parent/child tables on relationship B.a - there are no foreign keys linking these tables. Ensure that referencing columns are associated with a ForeignKey or ForeignKeyConstraint, or specify a 'primaryjoin' expression.

But this exception is lost here

graphene-sqlalchemy/graphene_sqlalchemy/utils.py

Lines 21 to 27 in a2fe926

	def is_mapped_class(cls):
	try:
	class_mapper(cls)
	except (ArgumentError, UnmappedClassError):
	return False
	else:
	return True

(called from

graphene-sqlalchemy/graphene_sqlalchemy/types.py

Line 94 in a2fe926

assert is_mapped_class(model), (

)
making the debug process for a simple mistake a pain.

[cmcinroy]

This really makes troubleshooting model issues very difficult.
I hit this problem on a regular basis.

[DrPyser]

Yup, hit that problem too. It seems assertions are used a lot in the codebase, where proper exceptions would be more appropriate and yield more useful stack traces.

[dtamez]

It seems that this makes it impossible to use sqlalchemy-utils types.

[alefhsousa]

👍 I lost much time in troubleshooting to understand the real problem

[teelau]

Has anyone solved this?

[onlyanegg]

It seems like there are multiple solutions proposed for this. I was taking a look at this as well and was thinking of a different one. Something like the following. I was wondering why we are catching ArgumentError.

def __init_subclass_with_meta__(...):
        ...
        if not is_mapped_class(model):
            raise Exception(
                'You need to pass a valid SQLAlchemy Model in {}.Meta, received "{}".'.format(
                    cls.__name__, model
                )
            )
        # assert is_mapped_class(model), (
        #    "You need to pass a valid SQLAlchemy Model in " '{}.Meta, received "{}".'
        # ).format(cls.__name__, model)
        ...

def is_mapped_class(cls):
    try:
        class_mapper(cls)
    except (UnmappedClassError):
    #except (ArgumentError, UnmappedClassError):
        return False
    else:
        return True

[vietvudanh]

Why does this line not at least print out the stack trace? I spent 1 hours finding what the root cause before find out this issue.

[rmzr7]

@jkimbo can we merge #238 in?

[yesthesoup]

How annoying this is. For anyone else coming here with a Flask app, I had to comment out importing my graphqlview and schema.

in myproject/__init__.py

...
#from myproject.routes.graphql import graphql_view
...

def create_app():
    ...
    #app.add_url_rule('/graphql', view_func=graphql_view())

in myproject.routes.graphql, where schema.py was the problem

from flask_graphql import GraphQLView

from myproject.schema import schema
from myproject.routes.decorators import authentication_required

def graphql_view():
    return authentication_required(GraphQLView.as_view('graphql', schema=schema, graphiql=False))

this allowed me to flask shell without an error and when I tried to query a problematic model I got the real error.

[erikwrede]

As far as I can tell there are three separate PRs for this problem:

• Don't suppress SQLAlchemy errors when mapping classes #169
• Allow SQLAlchemy class mapping errors to propagate #281

Which contain the same code except for some requested changes. And this PR, which simply drops all the assertions:

• Removed assertions that were hiding exceptions #238

Is there any preferred approach, and what's the status on requested changes? @connorbrinton @MPickfield @zefciu