Adding a :polymorphic option to decorates_association

lib/draper/base.rb

@@ -67,6 +67,8 @@ module Draper
         return orig_association  if orig_association.nil?
         if options[:with]
           options[:with].decorate(orig_association)
+        elsif options[:polymorphic]
+          "#{orig_association.class}Decorator".constantize.decorate(orig_association)
         else
           reflection = model.class.reflect_on_association(association_symbol)
           "#{reflection.klass}Decorator".constantize.decorate(orig_association)

spec/draper/base_spec.rb

@@ -138,6 +138,13 @@ describe Draper::Base do
         subject.previous_version.should be_instance_of(SpecificProductDecorator)
       end
     end
+
+    context "for a polymorphic association" do
+      before(:each){ subject.class_eval{ decorates_association :thing, :polymorphic => true } }
+      it "causes the association to be decorated with the right decorator" do
+        subject.thing.should be_instance_of(SomeThingDecorator)
+      end
+    end
   end
 
   context('.decorates_associations') do

spec/spec_helper.rb

@@ -15,5 +15,7 @@ require './spec/support/samples/namespaced_product_decorator.rb'
 require './spec/support/samples/product.rb'
 require './spec/support/samples/product_decorator.rb'
 require './spec/support/samples/specific_product_decorator.rb'
+require './spec/support/samples/some_thing.rb'
+require './spec/support/samples/some_thing_decorator.rb'
 require './spec/support/samples/widget.rb'
 require './spec/support/samples/widget_decorator.rb'

spec/support/samples/product.rb

@@ -64,4 +64,8 @@ class Product < ActiveRecord::Base
   def previous_version
     Product.new
   end
+
+  def thing
+    SomeThing.new
+  end
 end

spec/support/samples/some_thing.rb

@@ -0,0 +1,2 @@
+class SomeThing < Product
+end

spec/support/samples/some_thing_decorator.rb

@@ -0,0 +1,3 @@
+class SomeThingDecorator < Draper::Base
+  decorates :some_thing
+end