Fix ordering by name on milestones page

We should sort by title because name is only an alias for
the title attribute on the milestone model.

app/models/milestone.rb

@@ -149,6 +149,10 @@ class Milestone < ActiveRecord::Base
       reorder(Gitlab::Database.nulls_last_order('due_date', 'ASC'))
     when 'due_date_desc'
       reorder(Gitlab::Database.nulls_last_order('due_date', 'DESC'))
+    when 'name_asc'
+      reorder(Arel::Nodes::Ascending.new(arel_table[:title].lower))
+    when 'name_desc'
+      reorder(Arel::Nodes::Descending.new(arel_table[:title].lower))
     when 'start_date_asc'
       reorder(Gitlab::Database.nulls_last_order('start_date', 'ASC'))
     when 'start_date_desc'

spec/models/milestone_spec.rb

@@ -310,4 +310,24 @@ describe Milestone do
       expect(milestone.participants).to eq [user]
     end
   end
+
+  describe '.sort_by_attribute' do
+    set(:milestone_1) { create(:milestone, title: 'Foo') }
+    set(:milestone_2) { create(:milestone, title: 'Bar') }
+    set(:milestone_3) { create(:milestone, title: 'Zoo') }
+
+    context 'ordering by name ascending' do
+      it 'sorts by title ascending' do
+        expect(described_class.sort_by_attribute('name_asc'))
+          .to eq([milestone_2, milestone_1, milestone_3])
+      end
+    end
+
+    context 'ordering by name descending' do
+      it 'sorts by title descending' do
+        expect(described_class.sort_by_attribute('name_desc'))
+          .to eq([milestone_3, milestone_1, milestone_2])
+      end
+    end
+  end
 end