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對於sqlalchemy,如果有一個具有orm關係屬性的對象,並且您創建了對象的實例並設置了關係屬性,那麼您的新對象將被添加到設置關係的會話中。例如:設置關係attr將對象添加到設置關係的會話。有沒有辦法阻止它?
from sqlalchemy import create_engine, Column, Integer, String, ForeignKey
from sqlalchemy.orm import relationship, Session
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class User(Base):
__tablename__ = 'users'
user_id = Column(Integer, primary_key=True)
name = Column(String)
class Address(Base):
__tablename__ = 'addresses'
address_id = Column(Integer, primary_key=True)
user_id = Column(Integer, ForeignKey(User.user_id),)
address = Column(String)
user = relationship(User, backref='addresses')
engine = create_engine('sqlite:///:memory:')
Base.metadata.create_all(engine)
session = Session(bind=engine)
bob = User()
bob.name = 'Bob'
session.add(bob)
session.commit()
bobs_addr = Address()
bobs_addr.user = bob
bobs_addr.address = "23 Bob's st."
# bobs_addr not added to the session
engine.echo = True
session.commit()
運行上面的輸出:
2011-05-23 12:07:23,461 INFO sqlalchemy.engine.base.Engine.0x...9a10 BEGIN (implicit)
2011-05-23 12:07:23,463 INFO sqlalchemy.engine.base.Engine.0x...9a10 SELECT users.user_id AS users_user_id, users.name AS users_name
FROM users
WHERE users.user_id = ?
2011-05-23 12:07:23,463 INFO sqlalchemy.engine.base.Engine.0x...9a10 (1,)
2011-05-23 12:07:23,466 INFO sqlalchemy.engine.base.Engine.0x...9a10 INSERT INTO addresses (user_id, address) VALUES (?, ?)
2011-05-23 12:07:23,466 INFO sqlalchemy.engine.base.Engine.0x...9a10 (1, "23 Bob's st.")
2011-05-23 12:07:23,467 INFO sqlalchemy.engine.base.Engine.0x...9a10 COMMIT
bobs_addr沒有添加到會話,所以我希望它不會被提交到數據庫,但設置bobs_addr.user = bob導致bobs_addr被添加到會話中。我如何阻止這種情況發生?
有一種解決方法,我知道,這是設置bobs_addr.user_id = bob.user_id,但我更願意使用關係attr。
很酷。閱讀http://www.sqlalchemy.org/docs/orm/relationships.html#sqlalchemy.orm.relationship可解釋原因。 – 2011-05-23 12:36:11