您可以require 'dm-aggregates'，之后您可以

Router.count(:email => "blake@gmail.com")

它将转化为

SELECT COUNT(*) FROM routers WHERE "email" = 'blake@gmail.com'

(尽管您会在Router.all(:email => "blake@gmail.com").count和dm-aggregates中得到相同的语句.)

(Although you'll get the same statement with Router.all(:email => "blake@gmail.com").count with dm-aggregates.)