Rails提取没有关系的记录并且有条件的记录

Question

I have a HomeMaker and PerDateUnavailability models. HomeMaker has_many per_date_unavailabilities . I want all home makers who don't have a record in per_date_unavailabilities and home makers who have record but not when the per_date_unavailabilties.unavailable_date = somedate

I usually do the first part when I want HomeMakers without a PerDateUnavailability record using HomeMaker.includes(:per_date_unavailabilities).where(per_date_unavailabilities: {id: nil})

and the second part of the condition using HomeMaker.joins(:per_date_unavailabilities).where.not(per_date_unavailabilities: {unavailable_date: Date.today})

How do I mix these?

Answer 1

The sql you need is somewhat like this:

select a.*
  from home_makers a left join per_date_unavailabilities b
  on a.id = b.home_maker_id
  where b.home_maker_id is NULL
  or b.unavailable_date IS NOT ?;

Expressing the or clause is a little tough in ActiveRecord, and its best we don't fight it. (Edited after OP's comment)

HomeMaker.joins("LEFT JOIN per_date_unavailabilities on per_date_unavailabilities.home_maker_id = home_makers.id")
.where("per_date_unavailabilities.home_maker_id IS NULL OR per_date_unavailabilities.unavailable_date != ?", somedate)