Question

I’m trying to create a factory_build class method for creating Redirect objects within an ActiveRecord collection (see below).

For example @website.redirects.factory_build(:code => 301) would return a new instance of a PermenantRedirect object. However, even though I am able to invoke the factory_build class method I can’t get access to the primary_key for @website. Is there a way to access @website.id from inside a collection or am i forced to pass it into the method call? Any other suggestions would also be welcome, maybe I’m not going about this in the right approach. thanks.

class Website < ActiveRecord::Base
  has_many :redirects
  has_many :permenant_redirects
  has_many :temporary_redirects
end

# Redirect is an abstract class it uses Rails Single Table Inheritance
class Redirect < ActiveRecord::Base
  def self.factory_build(attributes)
    status_code = attributes.delete(:code)
    case status_code
      when 301
        Website.find( ... ).permenant_redirects.new(attributes)
      when 302
        Website.find( ... ).temporary_redirects.new(attributes)
      else
        raise InvalidStatusCodeError
    end
  end
end

class TemporaryRedirect < Redirect
  def status
    302
  end
end

class PermenantRedirect < Redirect
  def status
    301
  end
end

Answer 1

You need to access the scope for this relationship in order to be able to properly construct these objects. This is available to a class method:

class Redirect < ActiveRecord::Base
  def self.factory_build(attributes)
    redirect_type =
      case (status_code = attributes.delete(:code))
      when 301
        PermanentRedirect
      when 302
        TemporaryRedirect
      else
        Redirect
      end

    redirect_type.new(attributes.merge(scoped.scope_for_create))
  end
end

I’ve taken the liberty of DRYing up your creation code because you had a lot of duplication in there. Also note that calling find only to exercise a relationship is a waste of resources. If you know the ID of the record, simply pass that along as an attribute unless you have a very good reason for retrieving it first.

The scoped.scope_for_create call returns attributes defined by your current scope or scopes. These are usually in the form of something like { 'website_id' => 101 } and can be passed through to your create call.