我知道如何复制或复制SQLAlchemy映射对象的问题被问了很多次。答案总是取决于需求或“复制”或“复制”的解释方式。
这是问题的一个专门版本,因为我得到了使用make_transient()
的技巧。
但我有一些问题。我真的不知道怎么处理主键。在我的用例中,PK总是由SQLA(或后台的DB)自动生成的。但这不会发生在新的重复对象上。
代码有点伪。
import sqlalchemy as sa
from sqlalchemy.orm.session import make_transient
_engine = sa.create_engine('postgres://...')
_session = sao.sessionmaker(bind=_engine)()
class MachineData(_Base):
__tablename__ = 'Machine'
_oid = sa.Column('oid', sa.Integer, primary_key=True)
class TUnitData(_Base):
__tablename__ = 'TUnit'
_oid = sa.Column('oid', sa.Integer, primary_key=True)
_machine_fk = sa.Column('machine', sa.Integer, sa.ForeignKey('Machine.oid'))
_machine = sao.relationship("MachineData")
def __str__(self):
return '{}.{}: oid={}(hasIdentity={}) machine={}(fk={})' \
.format(type(self), id(self),
self._oid, has_identity(self),
self._machine, self._machine_fk)
if __name__ == '__main__':
# any query resulting in one persistent object
obj = GetOneMachineDataFromDatabase()
# there is a valid 'oid', has_identity == True
print(obj)
# should i call expunge() first?
# remove the association with any session
# and remove its “identity key”
make_transient(obj)
# 'oid' is still there but has_identity == False
print(obj)
# THIS causes an error because the 'oid' still exsits
# and is not new auto-generated (what should happen in my
# understandings)
_session.add(obj)
_session.commit()
目前没有回答
相关问题 更多 >
编程相关推荐