Sql Rails activerecord内部连接自定义对象

我有以下课程：

class Want < ActiveRecord::Base
  has_many :cached_buy_offers, dependent: :destroy
end
class CachedBuyOffer < ActiveRecord::Base
  belongs_to :want
end

这和预期的一样。 我想生成以下sql：

select * from wants
inner join 
(select cached_buy_offers.want_id, max(buy_offer_cents) as max_buy_offer,           count(cached_buy_offers.want_id) as buy_offer_count
from cached_buy_offers
where cached_buy_offers.want_id in (1,2,3,4)
group by cached_buy_offers.want_id
order by max_buy_offer) as cached_buy_offers
on cached_buy_offers.want_id = wants.id

可以使用以下命令生成内部sql查询：

ids = [1,2,3,4]

CachedBuyOffer.select('cached_buy_offers.want_id, max(buy_offer_cents) as max_buy_offer, count(cached_buy_offers.want_id) as buy_offer_count').where('cached_buy_offers.want_id in (?)',ids).group('cached_buy_offers.want_id').order('max_buy_offer')

但当我尝试这样做时：

Want.joins(CachedBuyOffer.select ..... the above activerecord inner query)

抛出错误运行时错误：未知类：CachedBuyOffer

---

如何生成所需的sql？

.joins

将关联键作为参数，例如

Want.joins（：cached\u buy\u offer）

。您可以将查询从中链接出来

您可以使用

Arel.sql

ids = [1,2,3,4]

cached_buy_offer_subquery = CachedBuyOffer
.select('cached_buy_offers.want_id, 
  max(buy_offer_cents) as max_buy_offer, 
  count(cached_buy_offers.want_id) as buy_offer_count')
.where('cached_buy_offers.want_id in (?)',ids)
.group('cached_buy_offers.want_id')
.order('max_buy_offer').to_sql

Want.joins("INNER JOIN (#{Arel.sql(cached_buy_offer_subquery)}) cached_buy_offers ON cached_buy_offers.want_id = wants.id")

---

我在rails控制台中尝试了这一点，其中也定义了CachedBuyOffer。我还能够独立执行activerecord内部查询。那么您是否尝试过，

Want.joins（：cached_by_offer）。选择（…）

？

ids = [1,2,3,4]

cached_buy_offer_subquery = CachedBuyOffer
.select('cached_buy_offers.want_id, 
  max(buy_offer_cents) as max_buy_offer, 
  count(cached_buy_offers.want_id) as buy_offer_count')
.where('cached_buy_offers.want_id in (?)',ids)
.group('cached_buy_offers.want_id')
.order('max_buy_offer').to_sql

Want.joins("INNER JOIN (#{Arel.sql(cached_buy_offer_subquery)}) cached_buy_offers ON cached_buy_offers.want_id = wants.id")