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我在尝试更新使用外键作为主键一部分的行时遇到问题。这里有一个简单情况:SQLAlchemy:将表数据与外键合并
class Foo(Base):
__tablename__ = 'foo_table'
foo_id = Column(Integer, primary_key=True)
bar_id = Column(Integer, ForeignKey('bar_table.bar_id'), primary_key=True)
foo_data = Column(String(255))
bar = relationship('Bar', backref='foos', foreign_keys=[bar_id])
class Bar(Base):
__tablename__ = 'bar_table'
bar_id = Column(Integer, primary_key=True)
首先我将创建为foo_table
的条目:
f = Foo()
f.foo_id = 1
f.foo_data = 'Foo Data'
现在,我将在bar_table
创建行和关联两个:
b = Bar()
f.bar = b
太棒了!我们将添加f
到我们的会议,并承诺:
session.add(f)
session.commit()
现在假装我们碰上与同foo_id
的Foo
另一个实例,并与同一Bar
,但也有一些新的数据:
f = Foo()
f.foo_id = 1
f.foo_data = 'NEW Foo Data'
f.bar = b
很好!这一直发生,对吧?我会用session.merge()
代替session.add()
刚刚更新的foo_table
的信息:
session.merge(f)
但是,这不是很好!代码中断,我得到的回溯:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/Library/Python/2.7/site-packages/sqlalchemy/orm/session.py", line 1689, in merge
self._autoflush()
File "/Library/Python/2.7/site-packages/sqlalchemy/orm/session.py", line 1282, in _autoflush
self.flush()
File "/Library/Python/2.7/site-packages/sqlalchemy/orm/session.py", line 2004, in flush
self._flush(objects)
File "/Library/Python/2.7/site-packages/sqlalchemy/orm/session.py", line 2122, in _flush
transaction.rollback(_capture_exception=True)
File "/Library/Python/2.7/site-packages/sqlalchemy/util/langhelpers.py", line 60, in __exit__
compat.reraise(exc_type, exc_value, exc_tb)
File "/Library/Python/2.7/site-packages/sqlalchemy/orm/session.py", line 2086, in _flush
flush_context.execute()
File "/Library/Python/2.7/site-packages/sqlalchemy/orm/unitofwork.py", line 373, in execute
rec.execute(self)
File "/Library/Python/2.7/site-packages/sqlalchemy/orm/unitofwork.py", line 532, in execute
uow
File "/Library/Python/2.7/site-packages/sqlalchemy/orm/persistence.py", line 149, in save_obj
base_mapper, states, uowtransaction
File "/Library/Python/2.7/site-packages/sqlalchemy/orm/persistence.py", line 301, in _organize_states_for_save
state_str(existing)))
sqlalchemy.orm.exc.FlushError: New instance <Foo at 0x10a804590> with identity key (<class 'test.Foo'>, (1, 1)) conflicts with persistent instance <Foo at 0x1097a30d0>
有谁知道为什么此更新失败?