handles all sorts of collections with #present

As long as the object responds to #first it can be used as a collection.
Coincidentally, ActiveRecord::Relation does.

lib/grape/endpoint.rb

@@ -316,7 +316,7 @@ def present(object, options = {})
       entity_class = options.delete(:with)
 
       # auto-detect the entity from the first object in the collection
-      object_instance = object.is_a?(Array) ? object.first : object
+      object_instance = object.respond_to?(:first) ? object.first : object
 
       object_instance.class.ancestors.each do |potential|
         entity_class ||= (settings[:representations] || {})[potential]

spec/grape/entity_spec.rb

@@ -40,13 +40,24 @@ def app; subject end
       entity.stub!(:represent).and_return("Hiya")
 
       class TestObject; end
+      class FakeCollection
+        def first; TestObject.new; end
+      end
 
       subject.represent TestObject, :with => entity
       subject.get '/example' do
         present [TestObject.new]
       end
+
+      subject.get '/example2' do
+        present FakeCollection.new
+      end
+
       get '/example'
       last_response.body.should == "Hiya"
+
+      get '/example2'
+      last_response.body.should == "Hiya"
     end
 
     it 'pulls a representation from the class ancestor if it exists' do