Optimize namespace.has_parent? method

We can avoid doing an extra SQL query for loading parent when
only checking if parent exists.

Because in Github import service we use nested setting of groups
(so there is a situation when `group` is set but `group_id` not),
we check presence of both group_id and group.

app/models/namespace.rb

@@ -256,7 +256,7 @@ class Namespace < ApplicationRecord
   end
 
   def has_parent?
-    parent.present?
+    parent_id.present? || parent.present?
   end
 
   def root_ancestor

spec/models/group_spec.rb

@@ -880,22 +880,6 @@ describe Group do
     end
   end
 
-  describe '#has_parent?' do
-    context 'when the group has a parent' do
-      it 'is truthy' do
-        group = create(:group, :nested)
-        expect(group.has_parent?).to be_truthy
-      end
-    end
-
-    context 'when the group has no parent' do
-      it 'is falsy' do
-        group = create(:group, parent: nil)
-        expect(group.has_parent?).to be_falsy
-      end
-    end
-  end
-
   context 'with uploads' do
     it_behaves_like 'model with uploads', true do
       let(:model_object) { create(:group, :with_avatar) }

spec/models/namespace_spec.rb

@@ -933,4 +933,25 @@ describe Namespace do
       end
     end
   end
+
+  describe '#has_parent?' do
+    it 'returns true when the group has a parent' do
+      group = create(:group, :nested)
+
+      expect(group.has_parent?).to be_truthy
+    end
+
+    it 'returns true when the group has an unsaved parent' do
+      parent = build(:group)
+      group = build(:group, parent: parent)
+
+      expect(group.has_parent?).to be_truthy
+    end
+
+    it 'returns false when the group has no parent' do
+      group = create(:group, parent: nil)
+
+      expect(group.has_parent?).to be_falsy
+    end
+  end
 end