Question

I have these model classes:

class Song < ActiveRecord::Base  
  has_many :urls, as: :media
  has_one :url, as: :media
end

class Url < ActiveRecord::Base
  belongs_to :media, polymorphic: true
end

The strange thing here is that Song.first.url always returns nil, but Song.first.urls returns a list of urls.

Here is the generated SQL queries:

Song.includes(:url).first.url # => nil

Song Load (0.4ms)  SELECT `songs`.* FROM `songs` LIMIT 1
Url Load (0.4ms)  SELECT `urls`.* FROM `urls` WHERE `urls`.`media_type` = 'Song' AND `urls`.`media_id` IN (1)

Song.includes(:urls).first.urls # => [list of urls]

Song Load (0.7ms)  SELECT `songs`.* FROM `songs` LIMIT 1
Url Load (0.5ms)  SELECT `urls`.* FROM `urls` WHERE `urls`.`media_type` = 'Song' AND `urls`.`media_id` IN (1)

I’m running rails 3.2.0.rc2 on Ruby 1.9.2

Any ideas why this is happening?

Answer 1

This was my fault, I had accidently implemented my own Song#url method. It took me a while to find it.