Rails 5通过OR加入activerecord范围

Question

I would like to join 2 scopes with OR.

scope :unassigned, -> {
  where(dongle_id: nil)
}

scope :driverless, -> {
  left_outer_joins(:customer).where(customers: { id: nil })
}

Now I am doing this as I can't figure it out:

scope :inactive, -> {
  left_outer_joins(:customer).where(
    'customers.vehicle_id IS ? OR vehicles.dongle_id IS ?', nil, nil
  )
}

Answer 1

A scope represents a narrowing of a database query, such as where(color: :red).select('shirts.*').includes(:washing_instructions) ( https://api.rubyonrails.org/classes/ActiveRecord/Scoping/Named/ClassMethods.html#method-i-scope )

Joining scopes using OR condition is not possible. A scope narrows resultset with some filter. Chaining scopes together is equivalent to using scope filters at the same time, ie SQL's AND condition.

For your case when 2 scopes need to be joined with OR you could merge their resultsets:

Vehicle.unassigned.to_a | Vehicle.driverless.to_a

but it's better to write another scope, as you already did.

Answer 2

这是您要找的东西吗？

scope :inactive, -> { unassigned.or(driverless) }