Thanks for the pull-request. I am not using ruby 1.9 yet, so those changes are very welcome and removing the freeze's is fine by me too.

The reason why record cache does not allow for :limit > 1 queries is that it is usually combined with sorting and large amounts of data, in which case the DB is probably faster than retrieving all records first and then sort + limit in memory.

To make sure only the has_one case is supported by the index_cache, I propose:

def cacheable?(query)
  # allow limit of 1 for has_one and Class.find :id
  query.where_id(@index) && (query.limit.nil? || (query.limit == 1 && !query.sorted?))
end

Would it be possible to add a has_one relation to the test model and write some specs? Especially the part of cache invalidation on delete is now missing.

Thanks again for your contribution,
Orslumen

I added the test and put the sorted check

Thanks again for your contribution, it will be part of the next release.