Question

我有（工作）代码

counts = Registration.select('regulator_id').group('regulator_id').count
@regulators.each {|r| r.registration_count=counts[r.id]}

允许我显示每个Regulator有多少个注册。它生成的查询是：

SELECT COUNT("registrations"."regulator_id") AS count_regulator_id, regulator_id AS regulator_id FROM "registrations" GROUP BY regulator_id

我想将我的计数限制在最后一次搜索的注册中，查询如下：

select
  regulator_id, count(*)
from
  registrations inner join
  regulators on regulators.id = registrations.regulator_id
where
  registrations.updated_at > regulators.last_scrape_start
group by
  regulator_id

但我无法使用arel或find_by_sql来使用语法。我相信当你知道答案时这很简单，但到目前为止我花了很多钱。

提前致谢。

Answer 1

只需添加'joins'和'where'

Registration.joins(:regulator).where('registrations.updated_at > regulators.last_scrape_start').select('regulators.id').group('regulators.id').count

在Rails 3中按查询分组

1 个答案: