# File lib/mongo/collection.rb, line 327
    def save(doc, opts={})
      if doc.has_key?(:_id) || doc.has_key?('_id')
        id = doc[:_id] || doc['_id']
        update({:_id => id}, doc, opts.merge!({:upsert => true}))
        id
      else
        insert(doc, opts)
      end
    end