sqlalchemy經典映射關系問題

Question

我的任務是最終學習sqlAlchemy，這樣我才能在未來幾年中獲益。

我對sqlalchemy的文件很感興趣並且已經過去兩天了。 我很想學習經典的映射方式，而不是聲明性的，bc我想要連接的db存在，並且在它的所有表中都沒有唯一的id列。 根據這篇文章，經典映射是在這種情況下的方法

我一直在關注sqlalchemy網站上的經典示例，但我似乎無法找到正確的關系配置來實現這一點。

這是我的所有代碼：

engine = create_engine(
    "mssql+pyodbc://someaddress/test?driver=FreeTDS?TDS_version=8.0", echo=True)

metadata = MetaData(engine)

class User(object):

    def __repr__(self):
        return "<User(User_id='%s', name='%s', age='%s')>" % (
                            self.user_id, self.name, self.age)
class Email(object):

    def __repr__(self):
        return "<User(email_id='%s', address='%s', user_id='%s')>" % (
                            self.email_id, self.address, self.user_id)

users = Table('users', metadata,
    Column('user_id', Integer, primary_key=True),
    Column('name', String(40)),
    Column('age', Integer),
    schema='test.dbo.users')

mapper(User, users, properties={'Email': relationship(Email, primaryjoin=users.c.user_id==emails.c.user_id)})

emails = Table('emails', metadata,
    Column('email_id', Integer, primary_key=True),
    Column('address', String),
    Column('user_id', Integer, ForeignKey('test.dbo.users.user_id')),
    schema='test.dbo.emails')

mapper(Email, emails)

Session = sessionmaker(bind=engine)
session = Session()

mary = session.query(User, Email).filter(User.user_id == Email.user_id)

追求錯誤消息清楚表明它是映射器/關系是問題。

InvalidRequestError: One or more mappers failed to initialize - can't proceed with initialization of other mappers.  Original exception was: Could not determine join condition between parent/child tables on relationship User.Email - there are no foreign keys linking these tables.  Ensure that referencing columns are associated with a ForeignKey or ForeignKeyConstraint, or specify a 'primaryjoin' expression.

我嘗試了很多不同的東西來嘗試補救，但我無法深究它。

任何指向正確的方向將非常感謝！

我所使用的sqlalchemy版本是;

'1.0.12'

Answer 1

我運氣好了：

Column('user_id', Integer, ForeignKey('users.user_id')),

我還重新排序了表和映射代碼：

users = Table('users', metadata,
    Column('user_id', Integer, primary_key=True),
    Column('name', String(40)),
    Column('age', Integer))

emails = Table('emails', metadata,
    Column('email_id', Integer, primary_key=True),
    Column('address', String),
    # foreign key to table users
    Column('user_id', Integer, ForeignKey('users.user_id')))

mapper(Email, emails)

mapper(User, users, properties={
    'Email': relationship(
        Email, primaryjoin=users.c.user_id==emails.c.user_id)})