On Oct 26, 2011, at 1:04 PM, James Hartley wrote:
> On Wed, Oct 26, 2011 at 2:22 AM, Stefano Fontanelli <s.fontane...@asidev.com>
> wrote:
>
> Hi James,
> you cannot define two mapper properties that use the same name.
>
> Thank you. I truly appreciate your response. I can now implement the table
> interconnection while both classes are defined in the same file. My problem
> is when the classes are separated. Given the following two files:
> ========8<----------------------
> #!/usr/bin/env python
> """ user.py """
> 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'
>
> from user import User
>
> Base = declarative_base()
>
> class Address(Base):
> __tablename__ = 'addresses'
>
> id = Column(Integer, primary_key=True)
> email_address = Column(String, nullable=False)
> user_id = Column(Integer, ForeignKey('users.id'), nullable=False)
>
> user = relationship('User', backref=backref('addresses', order_by=id))
If you wish to locate classes based on their string name as you are doing in
relationship('User') here, the calling class (Address) must share the same
registry of names that the desired class (User) does. This registry is part of
the "Base". Therefore your entire application needs to have exactly one usage
of "declarative_base()", where all descending classes use the same Base object,
and not one usage per file. Additionally, both user.py and address.py must
be imported via the Python "import" statement before the mappings can be used.
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