Using active record's #merge to separate concerns

basic_models.rb

class User < ActiveRecord::Base
  has_many :dvds
end
class Dvd < ActiveRecord::Base
  belongs_to :user
end

dvd_scope.rb

class Dvd < ActiveRecord::Base
  belongs_to :user
  scope :unreturned, -> { where(returned: false) }
end

user_scope.rb

class User < ActiveRecord::Base
  scope :with_unreturned_dvds, joins(:dvd).where(dvd: { returned: false })
end

user_scope_with_merge.rb

class User < ActiveRecord::Base
  scope :with_unreturned_dvds, joins(:dvd).merge(Dvd.unreturned)
end