Peter Marklund's Home
When I upgraded to Rails 2.1 ActiveRecord partial updates were turned on, i.e. when you save a record only those attributes that have changed are saved to the database. In theory, if you have two almost simulateneous updates, and you have a validation rule across several columns, then those updates can render the database record in an invalid state. Of course, in practice, this is very unlikely to happen. Nevertheless, I decided to turn on optimistic locking to be on the safe side. It turned out optimistic locking caused more issues than it was worth. Suppose you have an Article model that has many instances of Chapter and also that the Article uses a counter cache. Then you can run into this issue:
article = Article.first
article.chapters.create(:name => "Summary")
# => UPDATE articles SET chapters_count = chapters_count + 1,
# lock_version = lock_version + 1 WHERE id = XXX;
article.publish_date = 1.days.from_now
# => throws ActiveRecord::StaleObjectError
I like partial updates though since they make it less likely that simulteneous updates will clobber, since you are only writing to the db what has changed. It also makes SQL statements in the log file more readable.
I'm abandoning optimistic locking for now though.