HAL support for an array of linked objects

This change does not affect the interface of the link method. The
options hash position can be a type of Array which conveys multiple
linked objects for a single relationship.

The specification tests were updated as a new rspec context so the
existing tests would not be affected.

fixes #58

lib/oat/adapters/hal.rb

@@ -3,7 +3,11 @@ module Oat
   module Adapters
     class HAL < Oat::Adapter
       def link(rel, opts = {})
-        data[:_links][rel] = opts if opts[:href]
+        if opts.is_a?(Array)
+          data[:_links][rel] = opts.select { |link_obj| link_obj.include?(:href) }
+        else
+          data[:_links][rel] = opts if opts[:href]
+        end
       end
 
       def properties(&block)

spec/adapters/hal_spec.rb

@@ -81,5 +81,23 @@
         )
       end
     end
+
+    let(:array_of_linked_objects_serializer) {
+      array_of_linked_objects_serializer_class.new(friendly_user, nil, Oat::Adapters::HAL)
+    }
+    let(:linked_objects_hash) { array_of_linked_objects_serializer.to_hash }
+
+    context 'with an array of linked objects' do
+      it 'produces a HAL-compliant hash' do
+        expect(linked_objects_hash.fetch(:_links).fetch(:related).size).to be 3
+        expect(linked_objects_hash.fetch(:_links)).to include(
+          :related => [
+            {:type=>"friend", :href=>"http://foo.bar.com/1"},
+            {:type=>"friend", :href=>"http://foo.bar.com/2"},
+            {:type=>"friend", :href=>"http://foo.bar.com/3"}
+          ]
+        )
+      end
+    end
   end
 end

spec/fixtures.rb

@@ -5,6 +5,7 @@ def self.included(base)
     base.let(:friend) { user_class.new('Joe', 33, 2, []) }
     base.let(:manager) { user_class.new('Jane', 29, 3, []) }
     base.let(:user) { user_class.new('Ismael', 35, 1, [friend], manager) }
+    base.let(:friendly_user) { user_class.new('Jeff', 33, 1, [friend, manager, user]) }
     base.let(:serializer_class) do
       Class.new(Oat::Serializer) do
         klass = self
@@ -50,6 +51,24 @@ def self.included(base)
           end
         end
 
+        def url_for(id)
+          "http://foo.bar.com/#{id}"
+        end
+      end
+    end
+    base.let(:array_of_linked_objects_serializer_class) do
+      Class.new(Oat::Serializer) do
+        schema do
+          type 'user'
+
+          link :self, :href => url_for(item.id)
+          link :related, item.friends.map { |friend|
+            {:type => 'friend', :href => url_for(friend.id)}
+          }.sort_by { |link_obj|
+            link_obj[:href]
+          }
+        end
+
         def url_for(id)
           "http://foo.bar.com/#{id}"
         end