如何获取更改字段的原始值? [英] How to get the original value of changed fields?

问题描述

我使用 sqlalchemy 作为我的 orm，并使用 declarative 作为 Base.

I'm using sqlalchemy as my orm, and use declarative as Base.

Base = declarative_base()
class User(Base):
    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    name = Column(String)

我的问题是，我怎么知道一个用户被修改了，以及如何在不查询数据库的情况下再次获取原始值?

My question is, how do I know a user has been modified, and how to get the original values without query database again?

user = Session.query(User).filter_by(id=user_id).first()
# some operations on user
....
# how do I know if the user.name has been changed or not?
...
# How do get the original name?

提前致谢！

更新

我发现了一种方法 get_history 可以获取字段的历史记录值，但我不确定它是否适合我的目的.

I found a method get_history can get the history value of a field, but I'm not sure if it is the correct method for my purpose.

from sqlalchemy.orm.attributes import get_history
user = Session.query(User).first()
print user.name  # 'Jack'
print get_history(user, 'name') # ((),['Jack'],())

user.name = 'Mike'
print get_history(user, 'name') # (['Mike'], (),['Jack'])

所以，我们可以检查get_history的值，但这是最好的方法吗?

So, we can check the value of get_history, but is it the best method?

推荐答案

要查看 user 是否已被修改，您可以检查 user in session.dirty.如果是并且你想撤销它，你可以执行

To see if user has been modified you can check if user in session.dirty. If it is and you want to undo it, you can execute

session.rollback()

但请注意，这会将会话的所有内容回滚到最后一个 session.commit().

but be advised that this will rollback everything for the session to the last session.commit().

如果你想获得原始值并且内存正确地为我服务，它是由 sqlalchemy.orm.attributes.get_history 实用程序函数返回的元组的第二个元素.你必须这样做

If you want to get the original values and memory serves me correctly, it's the second element of the tuple returned by the sqlalchemy.orm.attributes.get_history utility function. You would have to do

old_value = sqlalchemy.orm.attributes.get_history(user, 'attribute')[2]

对于您想要的每个属性.

for each attribute that you want.

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