查找没有关联has_many对象的所有对象

Question

在我的在线商店中,如果订单处于"已授权"状态并且尚未有任何关联的货件,则该订单已准备好发货.现在我这样做:

class Order < ActiveRecord::Base
    has_many :shipments, :dependent => :destroy

    def self.ready_to_ship
        unshipped_orders = Array.new
        Order.all(:conditions => 'state = "authorized"', :include => :shipments).each do |o|
            unshipped_orders << o if o.shipments.empty?
        end
        unshipped_orders
    end
end

有没有更好的办法？

Answer 1

在使用AREL的Rails 3中

Order.includes('shipments').where(['orders.state = ?', 'authorized']).where('shipments.id IS NULL')

Answer 2

您还可以使用常规查找语法查询关联:

Order.find(:all, :include => "shipments", :conditions => ["orders.state = ? AND shipments.id IS NULL", "authorized"])