Refactor package scopes to use arel nodes

Refactor package scopes that sort by a joined
table to use arel nodes to enable keyset pagination.

app/models/packages/package.rb

@@ -8,6 +8,23 @@ class Packages::Package < ApplicationRecord
   DISPLAYABLE_STATUSES = [:default, :error].freeze
   INSTALLABLE_STATUSES = [:default].freeze
 
+  enum package_type: {
+    maven: 1,
+    npm: 2,
+    conan: 3,
+    nuget: 4,
+    pypi: 5,
+    composer: 6,
+    generic: 7,
+    golang: 8,
+    debian: 9,
+    rubygems: 10,
+    helm: 11,
+    terraform_module: 12
+  }
+
+  enum status: { default: 0, hidden: 1, processing: 2, error: 3 }
+
   belongs_to :project
   belongs_to :creator, class_name: 'User'
 
@@ -72,12 +89,6 @@ class Packages::Package < ApplicationRecord
     if: :debian_package?
   validate :forbidden_debian_changes, if: :debian?
 
-  enum package_type: { maven: 1, npm: 2, conan: 3, nuget: 4, pypi: 5,
-                       composer: 6, generic: 7, golang: 8, debian: 9,
-                       rubygems: 10, helm: 11, terraform_module: 12 }
-
-  enum status: { default: 0, hidden: 1, processing: 2, error: 3 }
-
   scope :for_projects, ->(project_ids) { where(project_id: project_ids) }
   scope :with_name, ->(name) { where(name: name) }
   scope :with_name_like, ->(name) { where(arel_table[:name].matches(name)) }
@@ -133,10 +144,28 @@ class Packages::Package < ApplicationRecord
   scope :order_type_desc, -> { reorder(package_type: :desc) }
   scope :order_project_name, -> { joins(:project).reorder('projects.name ASC') }
   scope :order_project_name_desc, -> { joins(:project).reorder('projects.name DESC') }
-  scope :order_project_path, -> { joins(:project).reorder('projects.path ASC, id ASC') }
-  scope :order_project_path_desc, -> { joins(:project).reorder('projects.path DESC, id DESC') }
   scope :order_by_package_file, -> { joins(:package_files).order('packages_package_files.created_at ASC') }
 
+  scope :order_project_path, -> do
+    if Feature.enabled?(:arel_package_scopes)
+      keyset_order = keyset_pagination_order(join_class: Project, column_name: :path, direction: :asc)
+
+      joins(:project).reorder(keyset_order)
+    else
+      joins(:project).reorder('projects.path ASC, id ASC')
+    end
+  end
+
+  scope :order_project_path_desc, -> do
+    if Feature.enabled?(:arel_package_scopes)
+      keyset_order = keyset_pagination_order(join_class: Project, column_name: :path, direction: :desc)
+
+      joins(:project).reorder(keyset_order)
+    else
+      joins(:project).reorder('projects.path DESC, id DESC')
+    end
+  end
+
   after_commit :update_composer_cache, on: :destroy, if: -> { composer? }
 
   def self.only_maven_packages_with_path(path, use_cte: false)
@@ -196,6 +225,32 @@ class Packages::Package < ApplicationRecord
     end
   end
 
+  def self.keyset_pagination_order(join_class:, column_name:, direction: :asc)
+    join_table = join_class.table_name
+    asc_order_expression = Gitlab::Database.nulls_last_order("#{join_table}.#{column_name}", :asc)
+    desc_order_expression = Gitlab::Database.nulls_first_order("#{join_table}.#{column_name}", :desc)
+    order_direction = direction == :asc ? asc_order_expression : desc_order_expression
+    reverse_order_direction = direction == :asc ? desc_order_expression : asc_order_expression
+    arel_order_classes = ::Gitlab::Pagination::Keyset::ColumnOrderDefinition::AREL_ORDER_CLASSES.invert
+
+    ::Gitlab::Pagination::Keyset::Order.build([
+      ::Gitlab::Pagination::Keyset::ColumnOrderDefinition.new(
+        attribute_name: "#{join_table}_#{column_name}",
+        column_expression: join_class.arel_table[column_name],
+        order_expression: order_direction,
+        reversed_order_expression: reverse_order_direction,
+        order_direction: direction,
+        distinct: false,
+        add_to_projections: true
+      ),
+      ::Gitlab::Pagination::Keyset::ColumnOrderDefinition.new(
+        attribute_name: 'id',
+        order_expression: arel_order_classes[direction].new(Packages::Package.arel_table[:id]),
+        add_to_projections: true
+      )
+    ])
+  end
+
   def versions
     project.packages
            .including_build_info

config/feature_flags/development/arel_package_scopes.yml

+---
+name: arel_package_scopes
+introduced_by_url: 
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/331306
+milestone: '13.12'
+type: development
+group: group::package
+default_enabled: false

spec/models/packages/package_spec.rb

@@ -729,6 +729,49 @@ RSpec.describe Packages::Package, type: :model do
     end
   end
 
+  context 'sorting' do
+    let_it_be(:project) { create(:project, name: 'aaa' ) }
+    let_it_be(:project2) { create(:project, name: 'bbb' ) }
+    let_it_be(:package1) { create(:package, project: project ) }
+    let_it_be(:package2) { create(:package, project: project2 ) }
+    let_it_be(:package3) { create(:package, project: project2 ) }
+    let_it_be(:package4) { create(:package, project: project ) }
+
+    it 'orders packages by their projects name ascending' do
+      expect(Packages::Package.order_project_name).to eq([package1, package4, package2, package3])
+    end
+
+    it 'orders packages by their projects name descending' do
+      expect(Packages::Package.order_project_name_desc).to eq([package2, package3, package1, package4])
+    end
+
+    shared_examples 'order_project_path scope' do
+      it 'orders packages by their projects path asc, then package id asc' do
+        expect(Packages::Package.order_project_path).to eq([package1, package4, package2, package3])
+      end
+    end
+
+    shared_examples 'order_project_path_desc scope' do
+      it 'orders packages by their projects path desc, then package id desc' do
+        expect(Packages::Package.order_project_path_desc).to eq([package3, package2, package4, package1])
+      end
+    end
+
+    context 'with arel scope feature flag enabled' do
+      it_behaves_like 'order_project_path scope'
+      it_behaves_like 'order_project_path_desc scope'
+    end
+
+    context 'with feature flag disabled' do
+      before do
+        stub_feature_flags(arel_package_scopes: false)
+      end
+
+      it_behaves_like 'order_project_path scope'
+      it_behaves_like 'order_project_path_desc scope'
+    end
+  end
+
   describe '.order_by_package_file' do
     let_it_be(:project) { create(:project) }
     let_it_be(:package1) { create(:maven_package, project: project) }
@@ -743,6 +786,33 @@ RSpec.describe Packages::Package, type: :model do
     end
   end
 
+  describe '.keyset_pagination_order' do
+    let(:join_class) { nil }
+    let(:column_name) { nil }
+    let(:direction) { nil }
+
+    subject { described_class.keyset_pagination_order(join_class: join_class, column_name: column_name, direction: direction) }
+
+    it { expect { subject }.to raise_error(NoMethodError) }
+
+    context 'with valid params' do
+      let(:join_class) { Project }
+      let(:column_name) { :name }
+
+      context 'ascending direction' do
+        let(:direction) { :asc }
+
+        it { is_expected.to eq('projects.name asc NULLS LAST, "packages_packages"."id" ASC') }
+      end
+
+      context 'descending direction' do
+        let(:direction) { :desc }
+
+        it { is_expected.to eq('projects.name desc NULLS FIRST, "packages_packages"."id" DESC') }
+      end
+    end
+  end
+
   describe '#versions' do
     let_it_be(:project) { create(:project) }
     let_it_be(:package) { create(:maven_package, project: project) }