Ran into an issue when iterating over a many association in a before_save callback on a document. For an association named foos, `foos.inspect` would show the items but `foos.each` would never yield to the given block since it appears to be empty. The original issue I was tracking down was that instead of not yielding it was yielding instances of Mongo::Cursor instead of the association object. I haven't been able to recreate that case.
The partially broken by cf82ec6 where it allowed a single ID to be passed and it would work as expected. This also adds support for multiple IDs to be provided.