in_array

gistfile1.rb

        def first(options={})
          return nil if ids.blank?

          if sorted?
            matched_ids = klass.collection.distinct(:_id, query(options).criteria.to_hash)
            return nil if matched_ids.blank?
            matched_ids.sort_by! { |matched_id| ids.index(matched_id) }
            find!(matched_ids.first)
          else
            query(options).first
          end
        end