How to use scopes to join across multiple tables

Question

I am new to ROR and I am trying to understand scopes. In my current implementation I am getting all the Processors and displaying it in the view.

class ProcessorsController
  def index
    @processors = Processor.all    
  end
end

I want to modify this so I can get only the processors where the user is admin. This is how my relations are set up.

class Processor
  belongs_to :feed

  #SCOPES (what I have done so far)
  scope :feed, joins(:feed)
  scope :groups, joins(:feed => :groups).join(:user).where(:admin => true)
end

class Feed < ActiveRecord::Base
  has_and_belongs_to_many :groups
end

class Group < ActiveRecord::Base
  belongs_to :user
end

class User < ActiveRecord::Base
  has_many :groups
  scope :admin,     where(:admin     => true)
end

I was able to do this in my pry

pry(main)> Processor.find(63).feed.groups.first.user.admin?

PS: could someone provide some good resources where I could learn how to use scopes if the relationships are complex.

Answer 1

scope :with_admin, -> { joins(:feed => { :groups => :user }).where('users.admin' => true) }

As for the resources, have you gone through the official documentation on ActiveRecord joins?