Hi
I'm trying to use DeferredReflection to encapsulate my data model so that
it can easily be instantiated for different environments. However, I am
having trouble creating relationships with a NoForeignKeysError being
raised. I am guessing it is because the table metadata generation is being
deferred, there's not enough information to create the foreign key
information and therefore the relationships.
I've simplified my code to the following:
import sqlalchemy as sa
from sqlalchemy.orm import sessionmaker, relationship
from sqlalchemy.ext.declarative import declarative_base, DeferredReflection
Base = declarative_base(cls=DeferredReflection)
class Country(Base):
__tablename__ = 'country'
class User(Base):
__tablename__ = 'user'
country_id = sa.Column(sa.Integer, sa.ForeignKey('country.country_id'))
country = relationship("Country", uselist=False)
class MyModel(object):
def __init__(self, env):
self._engine = sa.create_engine("...")
Base.metadata.bind = self._engine
Base.prepare(self._engine)
def create_session_maker(self):
return sessionmaker(bind=self._engine)
# This code is run in another module.
mymodel = MyModel("DEV")
Session = model.create_session_maker()
session = Session()
l1 = session.query(User).all()
The following error comes back:
NoForeignKeysError: Could not determine join condition between parent/child
tables on relationship User.country - there are no foreign keys linking these
tables. Ensure that referencing columns are associated with a ForeignKey or
ForeignKeyConstraint, or specify a 'primaryjoin' expression.
Any suggestions on how I might get around this?
Thanks in advance,
Blair
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