Use BatchModelLoader for parent in GroupType

app/graphql/types/group_type.rb

@@ -8,14 +8,16 @@ module Types
 
     expose_permissions Types::PermissionTypes::Group
 
-    field :web_url, GraphQL::STRING_TYPE, null: true
+    field :web_url, GraphQL::STRING_TYPE, null: false
 
     field :avatar_url, GraphQL::STRING_TYPE, null: true, resolve: -> (group, args, ctx) do
       group.avatar_url(only_path: false)
     end
 
     if ::Group.supports_nested_objects?
-      field :parent, GroupType, null: true
+      field :parent, GroupType,
+            null: true,
+            resolve: -> (obj, _args, _ctx) { Gitlab::Graphql::Loaders::BatchModelLoader.new(Group, obj.parent_id).find }
     end
   end
 end

spec/graphql/resolvers/group_resolver_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Resolvers::GroupResolver do
+  include GraphqlHelpers
+
+  set(:group1) { create(:group) }
+  set(:group2) { create(:group) }
+
+  describe '#resolve' do
+    it 'batch-resolves groups by full path' do
+      paths = [group1.full_path, group2.full_path]
+
+      result = batch(max_queries: 1) do
+        paths.map { |path| resolve_group(path) }
+      end
+
+      expect(result).to contain_exactly(group1, group2)
+    end
+
+    it 'resolves an unknown full_path to nil' do
+      result = batch { resolve_group('unknown/project') }
+
+      expect(result).to be_nil
+    end
+  end
+
+  def resolve_group(full_path)
+    resolve(described_class, args: { full_path: full_path })
+  end
+end