仅检索关联的记录

Question

I need to find out the records which are at least associated to any one of the records.

I've this relationship:

Class Category < ActiveRecord::Base
  has_many :services
end

Class Service < ActiveRecord::Base
  has_many :team_leaders, through: :allocations
  has_many :workers, through: :allocations
end

I need to find out only those services which has at least one worker or one teamleader associated to it. How to do it?

Answer 1

I don't know how you could do this without writing some SQL, but this is how I would have done it:

Service.includes(:team_leaders, :workers).where('team_leaders.id is not null OR workers.id is not null').references(:team_leaders, :workers).all

Edit: adding .references (see comments below)

Answer 2

c = Category.first

c.services.each do |service|
 if Allocation.exists?(:service_id => service.id)
   puts service.name
   puts service.service_name
 end
end

It will list only those services which has associated workers and team_leaders.

Answer 3

试试这个查询

Service.joins(:team_leaders, :workers).where('team_leaders.id is not null or workers.id is not null')