Rails 4 scope on HABTM association

Question

I'm a rails newbie and I created a scope on a HABTM association, but I still think it looks unnatural, not elegant, so I think there must be a better way of doing it. Could anyone advise me if there is such better way? I've seen other posts where people have the same question (Scope for Self-joining HABTM Association) with no answer...

class User < ActiveRecord::Base
  has_and_belongs_to_many :roles, :join_table => :users_roles
end

class Role < ActiveRecord::Base
  has_and_belongs_to_many :users, :join_table => :users_roles
end

scope :by_role, lambda { |role_name| joins('join users_roles on users.id = users_roles.user_id').
                                    joins('join roles on users_roles.role_id = roles.id').
                                    where('roles.name = ?', role_name) }

Answer 1

try this. it is more optimized.

 scope :by_role,  ->(role) { joins(:roles).where(roles: { name: role }) }