On 07/29/2016 12:27 PM, bsdz wrote:
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:
|
importsqlalchemy assa
fromsqlalchemy.orm importsessionmaker,relationship
fromsqlalchemy.ext.declarative importdeclarative_base,DeferredReflection
Base=declarative_base(cls=DeferredReflection)
classCountry(Base):
__tablename__ ='country'
classUser(Base):
__tablename__ ='user'
country_id =sa.Column(sa.Integer,sa.ForeignKey('country.country_id'))
country =relationship("Country",uselist=False)
classMyModel(object):
def__init__(self,env):
self._engine =sa.create_engine("...")
Base.metadata.bind =self._engine
Base.prepare(self._engine)
defcreate_session_maker(self):
returnsessionmaker(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:Couldnotdetermine join condition between parent/child
tables on relationship User.country -there are noforeign keys linking
these tables.Ensurethat referencing columns are associated witha
ForeignKeyorForeignKeyConstraint,orspecify a 'primaryjoin'expression.
can't reproduce. Need information on database in use, and if distinct
schemas are involved. See below, and perhaps try to modify this test
case in your environment to reproduce your failure.
import sqlalchemy as sa
from sqlalchemy.orm import sessionmaker, relationship
from sqlalchemy.ext.declarative import declarative_base, DeferredReflection
e = sa.create_engine("sqlite://", echo=True)
e.execute("""
create table country (
country_id integer primary key
)
""")
e.execute("""
create table user (
user_id integer primary key,
country_id integer,
foreign key (country_id) references country(country_id)
)
""")
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 = e
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 = mymodel.create_session_maker()
session = Session()
l1 = session.query(User).all()
print(User.country.property.primaryjoin)
|
Any suggestions on how I might get around this?
Thanks in advance,
Blair
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