Question

尝试更新使用外键作为主键一部分的行时，我遇到了问题。这是一个简化的案例：

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，我将为foo_table：

创建一个条目

f = Foo()
f.foo_id = 1
f.foo_data = 'Foo Data'

现在我将在bar_table中创建一行并将两者关联起来：

b = Bar()
f.bar = b

大！我们将f添加到会话并提交：

session.add(f)
session.commit()

现在假装我们遇到Foo的另一个foo_id实例并且与同一个Bar相关，但有一些新数据：

f = Foo()
f.foo_id = 1
f.foo_data = 'NEW Foo Data'
f.bar = b

没关系！这种情况一直都在发生，对吧？我只会使用foo_table代替session.merge()更新session.add()中的信息：

session.merge(f)

但这不好！代码中断了，我得到了回溯：

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>

有谁知道为什么这次更新失败了？

Answer 1

我不确定是否有一个非常好的答案......我最终查询了我是否正在使用新数据。

因此，每当我创建Foo的新实例时，

old_foo = session.query(Foo).filter(Foo.id == id).all()
if old_foo:
    foo = old_foo[0]
else:
    foo = Foo()

这似乎并不理想，但我还没有找到另一种有效的解决方案。

SQLAlchemy：将表数据与外键合并

1 个答案: