Association Extensions & Named Scopes

gistfile1.rb

# This is how I would like the models
#
# Order has an extension on its order_transactions association to return the total amount of all the transactions
#
# I want to call this extension method while modifying the association via a named scope, but it doesn't work (see below).

class OrderTransaction < ActiveRecord::Base
  scope :purchases, where(:action => 'purchase')
  scope :refunds,   where(:action => 'credit')
end

class Order < ActiveRecord::Base
  has_many :order_transactions, :autosave => true do
    def total_amount
      sum(:amount) / 100.0
    end
  end
end

gistfile2.txt

# But it doesn't work

ree-1.8.7-2010.02 > o = Order.first
ree-1.8.7-2010.02 > o.order_transactions.total_amount
 => 18200 
ree-1.8.7-2010.02 > o.order_transactions.purchases.total_amount
NoMethodError: undefined method `total_amount' for #<ActiveRecord::Relation:0x1036ff230>
	from /Users/tim/.rvm/gems/ree-1.8.7-2010.02@corner/ruby/1.8/gems/activerecord-3.0.0.rc/lib/active_record/relation.rb:366:in `method_missing'
	from (irb):3

gistfile3.rb

# To have it work, I need to create an identical extension on both the association and named scopes. Not DRY!


class OrderTransaction < ActiveRecord::Base
  scope :purchases, where(:action => 'purchase') do
    def total_amount
      sum(:amount) / 100.0
    end
  end
  
  scope :refunds,   where(:action => 'credit') do
    def total_amount
      sum(:amount) / 100.0
    end
  end
end

class Order < ActiveRecord::Base
  has_many :order_transactions, :autosave => true do
    def total_amount
      sum(:amount) / 100.0
    end
  end
end

gistfile4.txt

# And now I can do what I want

ree-1.8.7-2010.02 > o = Order.first
ree-1.8.7-2010.02 > o.order_transactions.total_amount
 => 18200 
ree-1.8.7-2010.02 > o.order_transactions.purchases.total_amount
 => 18200 

gistfile5.rb

# Here's one solution:

module SummingExtension
  def total_amount
    sum(:amount) / 100.0
  end
end

class OrderTransaction < ActiveRecord::Base
  scope :purchases, where(:action => 'purchase') do
    include SummingExtension
  end
  
  scope :refunds,   where(:action => 'credit') do
    include SummingExtension
  end
end

class Order < ActiveRecord::Base
  has_many :order_transactions, :autosave => true, :extend => SummingExtension
end

hah, of course. yeah that works well. I might go through ARel later and see if theres an easy way to do something like I originally mentioned.