mongodb/mongo-ruby-driver — pull request #185 by TylerBrock (2013-04-04 14:36:30+00:00)
Title: RUBY-574 mongos readpref injection exclusive of special query

Mongos 2.0.X doesn't like receiving commands wrapped in special query parameters.

To fix this I made the logic for injecting the mongos $readPreference independent of the logic for transforming the query selector based on special fields.