Hi James,
you cannot define two mapper properties that use the same name.
Your User model specifies:
addresses = relationship('Address', order_by='Address.id', backref='user')
Your Address model specifies:
user = relationship('User', backref=backref('addresses', order_by=id))
in the User model you define a "backref='user'", which will create a
property 'Address.user' in the mapped entity, but it already exist!
Tha same in Address model: you define a backref named 'address' which
already exists in User entity.
I don't know you use case but there are two scenario.
1) 'addresses' and 'user' are the end of the same relationship, in this
case you must remove one relationship definition and use backref:
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
name = Column(String)
fullname = Column(String)
password = Column(String)
addresses = relationship('Address', order_by='Address.id',
backref='user')
class Address(Base):
__tablename__ = 'addresses'
id = Column(Integer, primary_key=True)
email_address = Column(String, nullable=False)
user_id = Column(Integer, ForeignKey('users.id <http://users.id>'))
2) addresses and user properties are two different relationships, then
you must renamed backrefs :)
Il 26/10/11 04.05, James Hartley ha scritto:
I suspect this is user error, but I am not ferreting out my mistake.
I'm porting some older code to SQLAlchemy 0.71 on top of Python
2.7.1. Code which had originally implemented foreign keys without
using REFERENCES clauses in CREATE TABLE statements previously ran
fine. Now, adding formal foreign keys isn't working. I have boiled
this down to the following variant on the example found in the
SQLAlchemy Documentation:
=====8<--------------------------------------
#!/usr/bin/env python
from sqlalchemy import create_engine, Column, ForeignKey, Integer, String
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker, relationship, backref
Base = declarative_base()
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
name = Column(String)
fullname = Column(String)
password = Column(String)
addresses = relationship('Address', order_by='Address.id',
backref='user')
def __init__(self, name, fullname, password):
self.name <http://self.name> = name
self.fullname = fullname
self.password = password
def __repr__(self):
return "<User('%s', '%s', '%s', '%s')>" % (self.id
<http://self.id>, self.name <http://self.name>, self.fullname,
self.password)
class Address(Base):
__tablename__ = 'addresses'
id = Column(Integer, primary_key=True)
email_address = Column(String, nullable=False)
user_id = Column(Integer, ForeignKey('users.id <http://users.id>'))
user = relationship('User', backref=backref('addresses', order_by=id))
def __init__(self, email):
self.email_address = email
def __repr__(self):
return "<Address('%s', '%s', '%s')>" % (self.id
<http://self.id>, self.email_address, self.user_id)
if __name__ == '__main__':
engine = create_engine('sqlite:///:memory:', echo=True)
Base.metadata.create_all(engine)
Session = sessionmaker(bind=engine)
session = Session()
user = User('jdoe', 'John Doe', 'password')
print user
session.add(user)
session.commit()
=====8<--------------------------------------
Execution yields the following traceback:
=====8<--------------------------------------
traceback (most recent call last):
File "./test.py", line 51, in <module>
user = User('jdoe', 'John Doe', 'password')
File "<string>", line 2, in __init__
File
"/usr/local/lib/python2.7/site-packages/sqlalchemy/orm/instrumentation.py",
line 309, in _new_state_if_none
state = self._state_constructor(instance, self)
File
"/usr/local/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py",
line 432, in __get__
obj.__dict__[self.__name__] = result = self.fget(obj)
File
"/usr/local/lib/python2.7/site-packages/sqlalchemy/orm/instrumentation.py",
line 157, in _state_constructor
self.dispatch.first_init(self, self.class_)
File "/usr/local/lib/python2.7/site-packages/sqlalchemy/event.py",
line 274, in __call__
fn(*args, **kw)
File
"/usr/local/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py",
line 2787, in _event_on_first_init
configure_mappers()
File
"/usr/local/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py",
line 2719, in configure_mappers
mapper._post_configure_properties()
File
"/usr/local/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py",
line 1035, in _post_configure_properties
prop.init()
File
"/usr/local/lib/python2.7/site-packages/sqlalchemy/orm/interfaces.py",
line 121, in init
self.do_init()
File
"/usr/local/lib/python2.7/site-packages/sqlalchemy/orm/properties.py",
line 905, in do_init
self._generate_backref()
File
"/usr/local/lib/python2.7/site-packages/sqlalchemy/orm/properties.py",
line 1376, in _generate_backref
self, mapper))
sqlalchemy.exc.ArgumentError: Error creating backref 'user' on
relationship 'User.addresses': property of that name exists on mapper
'Mapper|Address|addresses'
=====8<--------------------------------------
Any insight shared would be greatly appreciated. Thanks.
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