Interrogation¶ ↑

This is a little hack I came up with today when I got tired of duplicating logic in scopes and accessor methods. If I define a method in a model like this:

class Submarine < ActiveRecord::Base
  named_scope :on_surface, :conditions => {:location => 'surface'}
  named_scope :submerged, :conditions => {:location => 'under water'}
end

I should be able to interrogate the model like this without needing to define Submarine#on_surface? or Submarine#submerged?:

sub = Submarine.first => #<Submarine id: 1, location: 'surface'>
sub.on_surface? => true
sub.submerged? => false

How this works¶ ↑

This version contains a preliminary attempt at parsing simple conditions against a model’s attributes, with a fallback to the database for complicated conditions. Which means that some methods will hit your database on each call. Something to be aware of.

WARNING¶ ↑

The big problem here is that an object’s state is not always in sync with the database. I’ve thought about this a lot, and at this point I think it’s best to raise an exception when using these methods on dirty objects. I think handling dirty objects is beyond the scope of this little hack.

Copyright © 2009 Jim Benton, released under the MIT license