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Conditional associations

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Define multiple associations on the same associated class. From the Rails Way blog.

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  1. # assumes an associated Item class with a base_amount attribute
  2. # usage: 
  3. # in = @asset.incoming_items
  4.  
  5. class Asset < ActiveRecord::Base
  6.   has_many :items, :dependent => :destroy_all 
  7.   has_many :incoming_items, :class_name => 'Item', :conditions => "base_amount > 0"
  8.   has_many :outgoing_items, :class_name => 'Item', :conditions => "base_amount < 0"
  9. end
  10.  
  11. # alternative using with_scope for adding more conditions
  12. # usage: 
  13. # in = @asset.incoming(:all, :order => 'created_at desc', :limit => 15)
  14.  
  15. class Asset < ActiveRecord::Base
  16.   has_many :items, :dependent => :destroy_all do
  17.     def incoming(*args)
  18.       args = [:all] if args.empty?
  19.       with_scope(:find => { :conditions => 'base_amount > 0'}) { find(*args) }
  20.     end
  21.  
  22.     def outgoing(*args)
  23.       args = [:all] if args.empty?
  24.       with_scope(:find => { :conditions => 'base_amount < 0'}) { find(*args) }
  25.     end
  26.   end
  27. end

URL: http://www.therailsway.com/2007/1/8/assetsgraphed-part-1

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