Connect to multiple databases in a single schema

I'm trying to use multiple SQL databases in a single GraphQL schema. Unfortunately I haven't figured out a good way to do this.

I know I can use the context argument when calling the execute method, as documented in the graphene docs:

# connect to database sources
metadata = create_engine('sqlite:///metadata.sqlite3')
users = create_engine('sqlite:///users.sqlite3')
session1 = scoped_session(sessionmaker(bind=metadata))
session2 = scoped_session(sessionmaker(bind=users))

# execute query
result = schema.execute('query { allUsers { edges { node { name } } } }', context={'session': session2})

But this doesn't make sense because I'd have to determine which database to use based on the query. I should be able to pass the query in and the schema will handle that.

Flask-SQLAlchemy handles this well by binding the data source name to the SQLAlchemy model. I'd recommend doing something similar, documentation here.

SQLALCHEMY_DATABASE_URI = 'postgres://localhost/main'
SQLALCHEMY_BINDS = {
    'users':        'mysqldb://localhost/users',
    'appmeta':      'sqlite:////path/to/appmeta.db'
}

class User(db.Model):
    __bind_key__ = 'users'  # this binds the User model to the 'users' mysql database
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True)

If you don't want to do that, the SQLAlchemyObjectType could also be a good place to map it.

class UserNode(SQLAlchemyObjectType):
    meta:
        model = User
        interfaces = (graphene.relay.Node,)
        bind_key = 'users'

Any thoughts on working this in, or is there already a way to connect to multiple databases in a single schema?