Automatically decorate associations with decorates_association

lib/draper/base.rb

@@ -53,6 +53,22 @@ module Draper
       define_method(input){ @model }
     end
 
+    # Typically called withing a decorator definition, this method causes
+    # the assocation to be decorated when it is retrieved.
+    #
+    # @param [Symbol] name of association to decorate, like `:products`
+    def self.decorates_association(association_symbol)
+      define_method(association_symbol) do
+        orig_association = model.send(association_symbol)
+        return nil  if orig_association.nil?
+        if orig_association.respond_to? :proxy_reflection # The association is a collection
+          "#{orig_association.proxy_reflection.klass}Decorator".constantize.decorate(orig_association)
+        else
+          "#{orig_association.class}Decorator".constantize.decorate(orig_association)
+        end
+      end
+    end
+
     # Specifies a black list of methods which may *not* be proxied to
     # to the wrapped object.
     #

spec/draper/base_spec.rb

@@ -74,6 +74,27 @@ describe Draper::Base do
     end
   end
 
+  context(".decorates_association") do
+    context "for collection associations" do
+      before(:each){ subject.class_eval{ decorates_association :similar_products } }
+      it "causes the association's method to return a collection of wrapped objects" do
+        subject.similar_products.each{ |decorated| decorated.should be_instance_of(ProductDecorator) }
+      end
+    end
+
+    context "for a singular association" do
+      before(:each){ subject.class_eval{ decorates_association :previous_version } }
+      it "causes the association's method to return a single wrapped object if the association is singular" do
+        subject.previous_version.should be_instance_of(ProductDecorator)
+      end
+
+      it "causes the association's method to return nil if the association is nil" do
+        source.stub(:previous_version){ nil }
+        subject.previous_version.should be_nil
+      end
+    end
+  end
+
   context(".model / .to_model") do
     it "should return the wrapped object" do
       subject.to_model.should == source

spec/support/samples/product.rb

@@ -44,4 +44,16 @@ class Product < ActiveRecord::Base
   def block
     yield
   end
+
+  def similar_products
+    result = [Product.new, Product.new]
+    def result.proxy_reflection
+      OpenStruct.new(:klass => Product)
+    end
+    result
+  end
+
+  def previous_version
+    Product.new
+  end
 end