Question on Data Concurrency

rubyonrails-talk
1

In Rails 2.2.2, if I retrieve a record using a Model.find method (any of the finds), make changes to it, and then save it, is there a possibility that another user (on a different thread, maybe a faster machine) could read the same record after me, but update it before me? If so, then the other user's changes would be lost (a data concurrency problem).

How does Rails prevent this?

Is there a way to do something like Model.save_only_if_updated_at_is_unchanged ? Is there a find_and_lock, find_for_update, or other similar function?

This is different than dirty records, because it is comparing the record I have in my session to the same record in the database to ensure that *no one else* changed it.

Thank you,

Steve

2

In Rails 2.2.2, if I retrieve a record using a Model.find method (any of the finds), make changes to it, and then save it, is there a possibility that another user (on a different thread, maybe a faster machine) could read the same record after me, but update it before me? If so, then the other user's changes would be lost (a data concurrency problem).

Yes

How does Rails prevent this?

Is there a way to do something like Model.save_only_if_updated_at_is_unchanged ? Is there a find_and_lock, find_for_update, or other similar function?

Look up optimistic locking.

Fred