Fixed Collection#blank? to work

* Fixed delegation code in Collection to only forward methods explicitly
  defined in the model to it, rather than methods that could've been
  mixed in or inherited from Object.

[#976 state:resolved]

lib/dm-core/collection.rb

@@ -1321,7 +1321,7 @@ def sliced_query(offset, limit)
     #
     # @api public
     def method_missing(method, *args, &block)
-      if model.respond_to?(method)
+      if model.model_method_defined?(method)
         delegate_to_model(method, *args, &block)
       elsif relationship = relationships[method] || relationships[method.to_s.singular.to_sym]
         delegate_to_relationship(relationship, *args)

lib/dm-core/model.rb

@@ -566,21 +566,14 @@ def repositories
 
     # TODO: document
     # @api private
-    def resource_methods
-      resource_methods = Set.new
-
-      ancestors.each do |mod|
-        next unless mod <= DataMapper::Resource
-        resource_methods.merge(mod.instance_methods(false).map { |method| method.to_s })
-      end
-
-      resource_methods
+    def model_method_defined?(method)
+      model_methods.include?(method.to_s)
     end
 
     # TODO: document
     # @api private
     def resource_method_defined?(method)
-      resource_methods.include?(method)
+      resource_methods.include?(method.to_s)
     end
 
     private
@@ -675,5 +668,30 @@ def assert_valid # :nodoc:
         end
       end
     end
+
+    # TODO: document
+    # @api private
+    def model_methods
+      @model_methods ||= ancestor_instance_methods { |mod| mod.meta_class }
+    end
+
+    # TODO: document
+    # @api private
+    def resource_methods
+      @resource_methods ||= ancestor_instance_methods { |mod| mod }
+    end
+
+    # TODO: document
+    # @api private
+    def ancestor_instance_methods
+      methods = Set.new
+
+      ancestors.each do |mod|
+        next unless mod <= DataMapper::Resource
+        methods.merge(yield(mod).instance_methods(false).map { |method| method.to_s })
+      end
+
+      methods
+    end
   end # module Model
 end # module DataMapper

spec/public/shared/collection_shared_spec.rb

@@ -48,6 +48,22 @@
     end
   end
 
+  it { @articles.should respond_to(:blank?) }
+
+  describe '#blank?' do
+    describe 'when the collection is empty' do
+      it 'should be true' do
+        @articles.clear.blank?.should be_true
+      end
+    end
+
+    describe 'when the collection is not empty' do
+      it 'should be false' do
+        @articles.blank?.should be_false
+      end
+    end
+  end
+
   it { @articles.should respond_to(:clear) }
 
   describe '#clear' do