如何在mongoid.yml中的同一Rails环境中设置多个数据库(不同)连接？

development:
  clients:
    default:
      uri: mongodb://localhost:27017/myapp_development
      options:
        server_selection_timeout: 5000
    secondary:
      uri: mongodb://localhost:27017/myapp_secondary
      options:
        server_selection_timeout: 5000

test:
  clients:
    default:
      uri: mongodb://localhost:27017/myapp_test
      options:
        server_selection_timeout: 5000
    secondary:
      uri: mongodb://localhost:27017/myapp_test_secondary
      options:
        server_selection_timeout: 5000

production:
  clients:
    default:
      uri: <%= ENV['MONGODB_URI'] %>
      options:
        server_selection_timeout: 5000
    secondary:
      uri: <%= ENV['MONGODB_SECONDARY_URI'] %>
      options:
        server_selection_timeout: 5000

class User
  include Mongoid::Document
  using_connection(:secondary)

  # 模型定义...
end