Nick Kallen noted that the behavior of has_many_with_args can be accomplished using has_finder.

Too true!

Imagine a system in which Users send Whispers to one another. We would like to see Whispers scoped so that:

  • A User viewing their own Whispers should see all Whispers they have received

  • A User viewing another User’s Whispers should see only Whispers they themselves sent

With the clean chainable syntax provided by has_finder, this is straight-forward. We return associations directly (notice, no find calls) and isolate declaration of the scoping the behavior to the class affected by it.

class Whisper < ActiveRecord::Base
  has_finder :from, lambda { |sender| { :conditions => [ 'sender_id = ?', ] } }
class User < ActiveRecord::Base
  has_many :received_whispers, :foreign_key => 'recipient_id'
  def whispers_viewable_by user
    return whispers if self == user

How expressive is that? Business rules are cleanly captured in the models and our associations stay so limber!

Thanks to Pat Maddox for turning me on to has_finder, and Nick Kallen for writing it.

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