Atomic arithmetic in Rails

Question

I need to perform some atomic arithmetic in Rails but the only way I've found to do it for single objects is via the crude update_all class method, e.g.:

Account.update_all(["debits = debits + ?", amount], :id => id)

With collection associations, the update_all class method should be usable as an association method, since the collection will pass missing method calls on to the class with the relevant scope:

accounts.update_all(["debits = debits + ?", amount])

When dealing with collections, this is much nicer and less repetitive. However this doesn't work for singleton associations, i.e. belongs_to and has_one. The method_missing for AssociationProxy passes through to the target instance, which won't have an update_all instance method (naturally).

Is there a more elegant way to perform this arithmetic? Or is update_all as good as it gets?

Answer 1

You're not going to beat the performance of update_all on a large number of records by a longshot. Any reason not to use that and wrap it in a transaction?