集團通過查詢Rails中3

Question

我有（工作）代碼

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

，讓我來說明如何多個註冊有每穩壓器。它生成的查詢是：

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

我想限制我的數僅從去年刮的註冊，有喜歡的查詢：

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 

，但我不能讓語法要麼工作使用arel或find_by_sql。當你知道答案時，我相信這很簡單，但迄今爲止我花了很多時間。

在此先感謝。

Answer 1

只需添加 '聯接' 和 '地點'

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