Invalid SQLAlchemy Model

[rvandyk]

Hey guys I hope someone can help me on this, i'm really stuck....

database automaping:

engine = create_engine(" blablabla", convert_unicode=True)

db_session = scoped_session(sessionmaker(autocommit=False,
                                         autoflush=False,
                                         bind=engine))

Base = automap_base()
Base.prepare(engine, reflect=True, generate_relationship=_gen_relationship, name_for_scalar_relationship = name_for_scalar_relationship, classname_for_table=camelize_classname, name_for_collection_relationship=pluralize_collection)

Buyer = Base.classes.Buyer

Base.query = db_session.query_property()

schema :

import graphene
import json
from graphene import relay
from graphene_sqlalchemy import SQLAlchemyConnectionField, SQLAlchemyObjectType

from database import Buyer as BuyerModel

class Buyer(SQLAlchemyObjectType):

    class Meta:
        model = BuyerModel
        interfaces = (relay.Node, )

class Query(graphene.ObjectType):
    node = relay.Node.Field()
    all_buyers = SQLAlchemyConnectionField(Buyer)

schema = graphene.Schema(query=Query)

Produces the error :
AssertionError: You need to pass a valid SQLAlchemy Model in Buyer.Meta, received "<class 'sqlalchemy.ext.automap.Buyer'>".

[Fedalto]

There's probably something wrong with your SQLAlchemy models, and nothing to do with the graphene schema.
I recently opened #121 explaining a bug that graphene-sqlalchemy does not show you the actual error. Your can try to put a breakpoint in is_mapped_class to see the exception SQLAlchemy is throwing.

[rvandyk]

In a big moment of rage, I tried launching my app again and again even with the error.
Guess what, it worked, it launched and seemed to be working pretty fine.
Actually sometimes it works, sometimes it doesn't...
Never seen this before, god help me

[andre-c-andersen]

Thanks @Fedalto, I tried to dive in. Ultimately all is_mapped_class(model) does is call def manager_of_class(cls), in the orm/base.py module, the specified SqlAlchemy model class. It's a tiny function with does the following:

def manager_of_class(cls):
    return cls.__dict__.get(DEFAULT_MANAGER_ATTR, None)

... where DEFAULT_MANAGER_ATTR = '_sa_class_manager'.

In essence it requires that you're model has a field '_sa_class_manager' if not it returns None then propagates the error up.

I initially thought this was an issue with graphene-sqlalchemy, but now I've realized the error shows up because Base.metadata.reflect(...) wasn't called before using the models. In essence there was no metadata to work with.

[dschmide]

I dont quite understand this response. As far as I can tell you only updated the error assertion, then what was wrong about @rvandyk 's code? Should people use automap in conjunction with graphene-sqlalchemy or is this a bad approach? There is a lack of resources for this, thus I ended up here.

I use
metadata = db.MetaData(bind=engine)
and then
tablemodel = db.Table('table_name', metadata, autoload = true)

can I use this tablemodel for graphql schemas? Imo, people working with existing databases really shouldnt be required to go through defining these models manually if they can "just" read them from the databases automatically. Does this technically work?

[Bulletninja]

Thanks @Fedalto, I tried to dive in. Ultimately all is_mapped_class(model) does is call def manager_of_class(cls), in the orm/base.py module, the specified SqlAlchemy model class. It's a tiny function with does the following:

def manager_of_class(cls):
    return cls.__dict__.get(DEFAULT_MANAGER_ATTR, None)

... where DEFAULT_MANAGER_ATTR = '_sa_class_manager'.

In essence it requires that you're model has a field '_sa_class_manager' if not it returns None then propagates the error up.

I initially thought this was an issue with graphene-sqlalchemy, but now I've realized the error shows up because Base.metadata.reflect(...) wasn't called before using the models. In essence there was no metadata to work with.

Is there a way to make it call as soon as it is defined or is there another recommended solution? Right now i'm getting this error with very inconsistent behavior and i'm unable to debug it even if i put a breakpoint in that method 🤔

[aguaguilar]

Hello, I'm really late but I have a workaround.

class BuyerModel(Base):
    __table__ = Buyer

You can use it :-)

[flipbit03]

@aguaguilar can you clarify?

[abisek]

I ran into similar issue. I use graphene-sqlalchemy too but it may be a more common problem in sqlalchemy. It happens with two worded model names - FraudSignature, BuyerModel, etc. I had to explicitly define the relationship in models referring to two or more worded models. Similar associations with models with single word works.

class MyOtherClass(Base):
   #  buyer_models = relationship('BuyerModel')  # Did not work
   buyer_models = relationship('BuyerModel', primaryjoin='MyOtherClass.id == foreign(BuyerModel.my_other_class_id)',)

class BuyerModel(Base):
   ....

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