Method to rename a collection in mongo db which works even if the target collection exists

rename_collection.rb

# version of rename collection that drops the existing collection if present.
# the standard rename method on the collection object provided by the driver 
# throws an exception if the target collection exists
# http://docs.mongodb.org/manual/reference/command/renameCollection/
def self.rename_collection(db, old_name, new_name)
  cmd = BSON::OrderedHash.new
  database_name = db.name
  cmd[:renameCollection] = "#{database_name}.#{old_name}"
  cmd[:to] = "#{database_name}.#{new_name}"
  cmd[:dropTarget] = true
  puts "Renaming collection #{old_name} to #{new_name}"
  db.connection.db("admin").command(cmd)
end