Use root_ancestor of Namespace (and move it from EE)

app/models/namespace.rb

@@ -213,6 +213,10 @@ class Namespace < ActiveRecord::Base
     parent.present?
   end
 
+  def root_ancestor
+    ancestors.reorder(nil).find_by(parent_id: nil)
+  end
+
   def subgroup?
     has_parent?
   end

app/models/project.rb

@@ -501,7 +501,11 @@ class Project < ActiveRecord::Base
   end
 
   def root_namespace
-    @root_namespace ||= Gitlab::GroupHierarchy.new(Namespace.where(id: namespace_id)).roots.take
+    if namespace.has_parent?
+      namespace.root_ancestor
+    else
+      namespace
+    end
   end
 
   def lfs_enabled?

ee/app/models/ee/namespace.rb

@@ -43,10 +43,6 @@ module EE
       end
     end
 
-    def root_ancestor
-      ancestors.reorder(nil).find_by(parent_id: nil)
-    end
-
     def move_dir
       raise NotImplementedError unless defined?(super)
 

spec/ee/spec/models/ee/namespace_spec.rb

@@ -363,19 +363,6 @@ describe Namespace do
     end
   end
 
-  describe '#root_ancestor' do
-    it 'returns the top most ancestor', :nested_groups do
-      root_group = create(:group)
-      nested_group = create(:group, parent: root_group)
-      deep_nested_group = create(:group, parent: nested_group)
-      very_deep_nested_group = create(:group, parent: deep_nested_group)
-
-      expect(nested_group.root_ancestor).to eq(root_group)
-      expect(deep_nested_group.root_ancestor).to eq(root_group)
-      expect(very_deep_nested_group.root_ancestor).to eq(root_group)
-    end
-  end
-
   describe '#actual_plan' do
     context 'when namespace has a plan associated' do
       before do

spec/models/namespace_spec.rb

@@ -675,4 +675,17 @@ describe Namespace do
       expect(other_namespace.find_fork_of(project)).to eq(other_fork)
     end
   end
+
+  describe '#root_ancestor' do
+    it 'returns the top most ancestor', :nested_groups do
+      root_group = create(:group)
+      nested_group = create(:group, parent: root_group)
+      deep_nested_group = create(:group, parent: nested_group)
+      very_deep_nested_group = create(:group, parent: deep_nested_group)
+
+      expect(nested_group.root_ancestor).to eq(root_group)
+      expect(deep_nested_group.root_ancestor).to eq(root_group)
+      expect(very_deep_nested_group.root_ancestor).to eq(root_group)
+    end
+  end
 end