自定义选择的连接表 [英] Custom select on join table

问题描述

我用钢轨3.2，并试图使用ActiveRecord来查询我的数据库。 我有2 ActiveRecord模型，管理与秩序：

I'm using rails 3.2, and trying to use ActiveRecord to query my database. I have 2 activerecord models, Admin and Order:

class Admin < ActiveRecord::Base
  attr_accessible :email, :name
  has_many :orders
class Order < ActiveRecord::Base
  attr_accessible :operation
  belongs_to :admin

在我的情况下，order.operation是一个字符串，再presenting订单类型。我试图建立一个查询给我三列：

In my case, order.operation is a string, representing order type. I'm trying to build a query giving me three columns:

admin.name, admin.orders.where(:operation => 'bonus').count, admin.orders.where(:operation => 'gift').count

有没有办法在一个查询中，以适应呢？

Is there a way to fit it in a single query?

编辑： 这里的原始SQL得到我所需要的：

EDITED: here's raw sql to get what I need:

SELECT t_a.admin_id_com, t_a.name, gb_f_f_gb_f_fi.bonus_count, gb_f_f_gb_f_fi.gifts_count 
FROM (
  SELECT f_fil.admin_id_gifts, f_fil.gifts_count, f_filt.admin_id_bonus, f_filt.bonus_count 
  FROM (
    SELECT admin_id as admin_id_gifts, count(distinct id) as gifts_count FROM orders WHERE operation = 'new gifts!' GROUP BY admin_id_gifts) 
  f_fil LEFT OUTER JOIN (
    SELECT admin_id as admin_id_bonus, count(distinct id) as bonus_count FROM orders WHERE operation = 'new bonuses!' GROUP BY admin_id_bonus) 
  f_filt ON (f_fil.admin_id_gifts = f_filt.admin_id_bonus)) 
gb_f_f_gb_f_fi LEFT OUTER JOIN (
  SELECT id AS admin_id_com, t_ad.name FROM admins t_ad) t_a ON (gb_f_f_gb_f_fi.admin_id_gifts = t_a.admin_id_com)

是否有可能像打造专业化的查询，使用ActiveRecord的？

Is it possible to buid a query like that using ActiveRecord?

推荐答案

试试这个：

@admins   = Admin.joins(:orders).
                 select("admins.id, admins.name, orders.id, 
                          SUM((orders.operation = 'bonus')::integer) AS bonus_count, 
                          SUM((orders.operation = 'gift')::integer) AS gift_count ").
                 group("admins.id ")

# access each columns as
admin.name, admin.bonus_count, admin.gift_count

另一种选择是使用预先加载，它会使用两个查询，但可能会更快

Other option is to use eager loading, it will use two queries but might be faster

@admins  = Admin.includes(:orders)

# in admin.rb
def orders_count(type)
  # Don't use where here as it would make a separate query instead of using eager loading records
   orders.select{|x| x.operation == type}.count
end 

# access each columns as
admin.name, admin.orders_count("bonus"), admin.orders_count("gift")

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