adding :find_by option to load_resource - closes #19

lib/cancan/controller_additions.rb

@@ -80,6 +80,11 @@ module CanCan
       # [:+instance_name+]
       #   The name of the instance variable to load the resource into.
       #
+      # [:+find_by+]
+      #   Find using a different attribute other than id. For example.
+      #
+      #     load_resource :find_by => :permalink # will use find_by_permlink!(params[:id])
+      #
       # [:+collection+]
       #   Specify which actions are resource collection actions in addition to :+index+. This
       #   is usually not necessary because it will try to guess depending on if the id param is present.

lib/cancan/controller_resource.rb

@@ -53,7 +53,11 @@ module CanCan
     end
 
     def find_resource
-      @options[:singular] ? resource_base.send(name) : resource_base.find(id_param)
+      if @options[:singular]
+        resource_base.send(name)
+      else
+        @options[:find_by] ? resource_base.send("find_by_#{@options[:find_by]}!", id_param) : resource_base.find(id_param)
+      end
     end
 
     def authorization_action

spec/cancan/controller_resource_spec.rb

@@ -218,6 +218,14 @@ describe CanCan::ControllerResource do
     @controller.instance_variable_get(:@custom_ability).should == :some_ability
   end
 
+  it "should load resource using custom find_by attribute" do
+    @params.merge!(:action => "show", :id => 123)
+    stub(Ability).find_by_name!(123) { :some_resource }
+    resource = CanCan::ControllerResource.new(@controller, :find_by => :name)
+    resource.load_resource
+    @controller.instance_variable_get(:@ability).should == :some_resource
+  end
+
   it "should raise ImplementationRemoved when adding :name option" do
     lambda {
       CanCan::ControllerResource.new(@controller, :name => :foo)