如何确保致电已更改？ 事务回滚后在ActiveRecord模型的实例上返回true？

Question

I found an issue in my code where a transaction block is rollback by explicitly raising an ActiveRecord::Rollback. In this case if an instance of a model saves successfully in the transaction before the rollback it ends up in a weird state.

Here is an example of a simple case that causes the issue:

record = SomeModel.last
record.attributes = { name: "A New Name"}

SomeModel.transaction do 
  record.save
  raise ActiveRecord::Rollback
end

If I called record.changed? after the transaction this will return false. However, if I call record.name after the transaction I would get a "A New Name". For some reason in this case the record has changes that were not persisted in the database, but ActiveRecord is not identifying these as changes anymore.

In my real-world application this is causing an issue in one area I use transactions. I have code where if a transaction fails I attempt to retry the transaction again with some changed parameters. If I reuse the instance that went through the first transaction without reloading it this results in the changes not being saved since they don't appear as changes.

Does anyone have any suggestions how to ensure that the instance has the changes and ActiveRecord still identifies these as changes?

Answer 1

ActiveRecord works this way, because it works this way. I can imagine scenarios in which it would be useful to reload the object from the database after rolling back a transaction. I can imagine scenarios in which it would not. Like, maybe I want to preserve the "new" fields to log the values our to show them to the user.

You just need to work with the way it works. Since ActiveRecord doesn't reload the object after a transaction rollback you have to do it yourself. I suppose you could also subclass the code to do what you want.

As for the dirty behavior. It says in the docs that all the dirty tracking behavior is lost after calling save. That the transaction rollback doesn't preserve this information does seem inconsistent and annoying. Perhaps a rubyist can explain exactly why it has to be this way, though it makes sense from the way I imagine the code to be structured. ActiveRecord has been around forever. I wouldn't hold my breath for it to work differently in this regard.