Add a separate finder for collecting children of groups

app/finders/group_children_finder.rb

+class GroupChildrenFinder
+  include Gitlab::Allowable
+
+  attr_reader :current_user, :parent_group, :params
+
+  def initialize(current_user = nil, parent_group:, params: {})
+    @current_user = current_user
+    @parent_group = parent_group
+    @params = params
+  end
+
+  def execute
+    Kaminari.paginate_array(children)
+  end
+
+  # This allows us to fetch only the count without loading the objects. Unless
+  # the objects were already loaded.
+  def total_count
+    @total_count ||= if defined?(@children)
+                       children.size
+                     else
+                       child_groups.count + projects.count
+                     end
+  end
+
+  private
+
+  def children
+    @children ||= child_groups + projects
+  end
+
+  def child_groups
+    return Group.none unless Group.supports_nested_groups?
+    return Group.none unless can?(current_user, :read_group, parent_group)
+
+    groups = GroupsFinder.new(current_user,
+                              parent: parent_group,
+                              all_available: true,
+                              all_children_for_parent: params[:filter_groups].present?).execute
+
+    groups = groups.search(params[:filter]) if params[:filter].present?
+    groups = groups.includes(:route).includes(:children)
+    groups.sort(params[:sort])
+  end
+
+  def projects
+    return Project.none unless can?(current_user, :read_group, parent_group)
+
+    projects = GroupProjectsFinder.new(group: parent_group, params: params, current_user: current_user).execute
+    projects = projects.includes(:route)
+    projects = projects.search(params[:filter]) if params[:filter].present?
+    projects.sort(params[:sort])
+  end
+end

spec/finders/group_children_finder_spec.rb

+require 'spec_helper'
+
+describe GroupChildrenFinder do
+  let(:user) { create(:user) }
+  let(:group) { create(:group) }
+  let(:params) { {} }
+  subject(:finder) { described_class.new(user, parent_group: group, params: params) }
+
+  before do
+    group.add_owner(user)
+  end
+
+  describe '#execute' do
+    it 'includes projects' do
+      project = create(:project, namespace: group)
+
+      expect(finder.execute).to contain_exactly(project)
+    end
+
+    context 'with a filter' do
+      let(:params) { { filter: 'test' } }
+
+      it 'includes only projects matching the filter' do
+        _other_project = create(:project, namespace: group)
+        matching_project = create(:project, namespace: group, name: 'testproject')
+
+        expect(finder.execute).to contain_exactly(matching_project)
+      end
+    end
+  end
+
+  context 'with nested groups', :nested_groups do
+    let!(:project) { create(:project, namespace: group) }
+    let!(:subgroup) { create(:group, parent: group) }
+
+    describe '#execute' do
+      it 'contains projects and subgroups' do
+        expect(finder.execute).to contain_exactly(subgroup, project)
+      end
+
+      context 'with a filter' do
+        let(:params) { { filter: 'test' } }
+
+        it 'contains only matching projects and subgroups' do
+          matching_project = create(:project, namespace: group, name: 'Testproject')
+          matching_subgroup = create(:group, name: 'testgroup', parent: group)
+
+          expect(finder.execute).to contain_exactly(matching_subgroup, matching_project)
+        end
+      end
+    end
+
+    describe '#total_count' do
+      it 'counts the array children were already loaded' do
+        finder.instance_variable_set(:@children, [double])
+
+        expect(finder).not_to receive(:child_groups)
+        expect(finder).not_to receive(:projects)
+
+        expect(finder.total_count).to eq(1)
+      end
+
+      it 'performs a count without loading children when they are not loaded yet' do
+        expect(finder).to receive(:child_groups).and_call_original
+        expect(finder).to receive(:projects).and_call_original
+
+        expect(finder.total_count).to eq(2)
+      end
+    end
+  end
+end