[Rails] RANT: belongs_to -> refers_to

[Tobias Lütke]

Improve your code

class Picture < AR:B
   acts_as_list
end

class Item < ActiveRecord::Base
  has_one :primary_picture, :class_name => 'Picture', :order => 'position ASC'
end

On 4/2/06, Jay Levitt <jay+news at jay.fm> wrote:
> Every once in a while, I pipe up and whine that "belongs_to" should really
> be 'refers_to" [http://dev.rubyonrails.org/ticket/2130].  It's time again.
>
> I've got a bunch of stuff going onto eBay, so, like any good engineer, I
> don't just post it manually: I design a Rails-based inventory database that
> creates a semantically-correct XHTML/CSS auction posting with a variable
> number of thumbnails (stored with file_column) and Textile fields.
>
> I start out with
>
> class Item < ActiveRecord::Base
>   :has_many :pictures
> end class
>
> But I want one of those pictures to be featured as the gallery photo.  So,
> naturally, I gravitate towards adding
>
> class Item < ActiveRecord::Base
>   :has_one primary_picture, :class_name => 'Picture'
> end
>
> I am encouraged in this futile pursuit by the docs, which I quickly skim to
> see things like
>
>   :has_one :last_comment, :class_name => "Comment", :order => "posted_on"
>
> Of course, in the light of day, it's clear that this automagically creates
> the last_comment association by picking the most recent comment.  But at
> 3am, it just reinforced the tendency to use has_one.  Ditto the many other
> has_one examples I found - half of which used the automatic-first-record
> feature, and half of which were probably just making the same mistake I
> was.
>
> I started getting nil objects, and was mystified until I finally tried
> explicitly setting the foreign key:
>
>   :has_one primary_picture, :class_name => 'Picture',
>     :foreign_key => 'primary_picture_id'
>
> at which point Rails helpfully told me that there was no
> Picture.primary_picture_id field.  Then I remembered for the umpteenth time
> that has_one is for the record that does NOT have the foreign key, and
> belongs_to is for the one that does, and I should not be misled by the
> semantics of the actual has_one and belongs_to keywords.
>
> Item :belongs_to primary_picture makes no sense.  Item :refers_to
> primary_picture does.  This is way too small for even a plugin - and I
> don't think that type of syntax change belongs in a plugin, anyway.  I have
> yet to hear anyone who's opposed to it... can't we PLEASE add this alias
> and consider deprecating belongs_to over time?  It's... just... wrong.
>
> Jay Levitt
>
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Tobi
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