Add UninferrableDecoratorError

lib/draper.rb

@@ -18,3 +18,11 @@ require 'draper/railtie' if defined?(Rails)
 # Test Support
 require 'draper/test/rspec_integration'    if defined?(RSpec) and RSpec.respond_to?(:configure)
 require 'draper/test/minitest_integration' if defined?(MiniTest::Rails)
+
+module Draper
+  class UninferrableDecoratorError < NameError
+    def initialize(klass)
+      super("Could not infer a decorator for #{klass}.")
+    end
+  end
+end

lib/draper/collection_decorator.rb

@@ -65,7 +65,7 @@ module Draper
       singular_name = name.chomp("Decorator").singularize
       "#{singular_name}Decorator".constantize
     rescue NameError
-      raise NameError, "Could not infer a decorator for #{name}. Please specify the decorator class when creating instances of this class."
+      raise Draper::UninferrableDecoratorError.new(self)
     end
   end
 end

lib/draper/decoratable.rb

@@ -25,12 +25,14 @@ module Draper::Decoratable
 
   module ClassMethods
     def decorate(options = {})
-      decorator_proxy = decorator_class.decorate(self.scoped, options)
-      block_given? ? yield(decorator_proxy) : decorator_proxy
+      collection_decorator = decorator_class.decorate(self.scoped, options)
+      block_given? ? yield(collection_decorator) : collection_decorator
     end
 
     def decorator_class
       "#{model_name}Decorator".constantize
+    rescue NameError
+      raise Draper::UninferrableDecoratorError.new(self)
     end
   end
 end

spec/draper/collection_decorator_spec.rb

@@ -90,7 +90,7 @@ describe Draper::CollectionDecorator do
     end
 
     it "raises when decorates an empty array without the klass" do
-      expect{EnumerableProxy.decorate([])}.to raise_error
+      expect{EnumerableProxy.decorate([])}.to raise_error Draper::UninferrableDecoratorError
     end
   end
 

spec/draper/decoratable_spec.rb

@@ -25,7 +25,7 @@ describe Draper::Decoratable do
 
   describe "#decorated_with?" do
     it "returns false" do
-      subject.should_not be_decorated_with(ProductDecorator)
+      subject.should_not be_decorated_with ProductDecorator
     end
   end
 
@@ -35,6 +35,20 @@ describe Draper::Decoratable do
     end
   end
 
+  describe ".decorator_class" do
+    context "when the decorator can be inferred from the model" do
+      it "returns the inferred decorator class" do
+        Product.decorator_class.should be ProductDecorator
+      end
+    end
+
+    context "when the decorator can't be inferred from the model" do
+      it "throws an UninferrableDecoratorError" do
+        expect{UninferrableDecoratorModel.decorator_class}.to raise_error Draper::UninferrableDecoratorError
+      end
+    end
+  end
+
   describe Draper::Decoratable::ClassMethods do
     shared_examples_for "a call to Draper::Decoratable::ClassMethods#decorate" do
       subject { klass.limit }

spec/spec_helper.rb

@@ -25,6 +25,7 @@ require './spec/support/samples/sequel_product'
 require './spec/support/samples/specific_product_decorator'
 require './spec/support/samples/some_thing'
 require './spec/support/samples/some_thing_decorator'
+require './spec/support/samples/uninferrable_decorator_model'
 require './spec/support/samples/widget'
 require './spec/support/samples/widget_decorator'
 

spec/support/samples/uninferrable_decorator_model.rb

@@ -0,0 +1,3 @@
+class UninferrableDecoratorModel
+  include Draper::Decoratable
+end