集团通过查询Rails中3

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]} 

，让我来说明如何多个注册有每稳压器。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 

我想限制我的数仅从去年刮的注册，有喜欢的查询：

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 

，但我不能让语法要么工作使用arel或find_by_sql。当你知道答案时，我相信这很简单，但迄今为止我花了很多时间。

在此先感谢。

Answer 1

只需添加 '联接' 和 '地点'

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