Add resource weight tracking

Revert schema changes

Apply schema changes

Add feature flag test

Add foreign keys

Remove explicit key removal

app/models/resource_weight_event.rb

+# frozen_string_literal: true
+
+class ResourceWeightEvent < ApplicationRecord
+  validates :user, presence: true
+  validates :issue, presence: true
+
+  belongs_to :user
+  belongs_to :issue
+
+  scope :by_issue, ->(issue) { where(issue_id: issue.id) }
+end

db/migrate/20191210211253_create_resource_weight_event.rb

+# frozen_string_literal: true
+
+class CreateResourceWeightEvent < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    create_table :resource_weight_events do |t|
+      t.integer :user_id, null: false
+      t.integer :issue_id, null: false
+      t.integer :weight
+      t.datetime_with_timezone :created_at, null: false
+
+      t.index [:user_id], name: 'index_resource_weight_events_on_user_id'
+      t.index [:issue_id, :weight], name: 'index_resource_weight_events_on_issue_id_and_weight'
+    end
+
+    add_concurrent_foreign_key :resource_weight_events, :users, column: :user_id, on_delete: :cascade
+    add_concurrent_foreign_key :resource_weight_events, :issues, column: :issue_id, on_delete: :cascade
+  end
+
+  def down
+    drop_table :resource_weight_events
+  end
+end

db/schema.rb

@@ -3605,6 +3605,15 @@ ActiveRecord::Schema.define(version: 2019_12_18_225624) do
     t.index ["user_id"], name: "index_resource_label_events_on_user_id"
   end
 
+  create_table "resource_weight_events", force: :cascade do |t|
+    t.integer "user_id", null: false
+    t.integer "issue_id", null: false
+    t.integer "weight"
+    t.datetime_with_timezone "created_at", null: false
+    t.index ["issue_id", "weight"], name: "index_resource_weight_events_on_issue_id_and_weight"
+    t.index ["user_id"], name: "index_resource_weight_events_on_user_id"
+  end
+
   create_table "reviews", force: :cascade do |t|
     t.integer "author_id"
     t.integer "merge_request_id", null: false
@@ -4745,6 +4754,8 @@ ActiveRecord::Schema.define(version: 2019_12_18_225624) do
   add_foreign_key "resource_label_events", "labels", on_delete: :nullify
   add_foreign_key "resource_label_events", "merge_requests", on_delete: :cascade
   add_foreign_key "resource_label_events", "users", on_delete: :nullify
+  add_foreign_key "resource_weight_events", "issues", name: "fk_5eb5cb92a1", on_delete: :cascade
+  add_foreign_key "resource_weight_events", "users", name: "fk_bfc406b47c", on_delete: :cascade
   add_foreign_key "reviews", "merge_requests", on_delete: :cascade
   add_foreign_key "reviews", "projects", on_delete: :cascade
   add_foreign_key "reviews", "users", column: "author_id", on_delete: :nullify

ee/app/models/concerns/ee/weight_eventable.rb

+# frozen_string_literal: true
+
+module EE
+  module WeightEventable
+    extend ActiveSupport::Concern
+
+    included do
+      has_many :resource_weight_events
+    end
+  end
+end

ee/app/models/ee/issue.rb

@@ -13,6 +13,7 @@ module EE
 
       include Elastic::ApplicationVersionedSearch
       include UsageStatistics
+      include WeightEventable
 
       scope :order_weight_desc, -> { reorder ::Gitlab::Database.nulls_last_order('weight', 'DESC') }
       scope :order_weight_asc, -> { reorder ::Gitlab::Database.nulls_last_order('weight') }

ee/app/services/ee/issuable/common_system_notes_service.rb

@@ -30,13 +30,25 @@ module EE
 
       def handle_weight_change_note
         if issuable.previous_changes.include?('weight')
-          create_weight_change_note
+          note = create_weight_change_note
+
+          track_weight_change(note)
         end
       end
 
       def create_weight_change_note
         ::SystemNoteService.change_weight_note(issuable, issuable.project, current_user)
       end
+
+      def track_weight_change(note)
+        return unless weight_changes_tracking_enabled?
+
+        EE::ResourceEvents::ChangeWeightService.new(issuable, current_user, note.created_at).execute
+      end
+
+      def weight_changes_tracking_enabled?
+        ::Feature.enabled?(:track_resource_weight_change_events, issuable.project)
+      end
     end
   end
 end

ee/app/services/ee/resource_events/change_weight_service.rb

+# frozen_string_literal: true
+
+module EE
+  module ResourceEvents
+    class ChangeWeightService
+      attr_reader :resource, :user, :event_created_at
+
+      def initialize(resource, user, created_at)
+        @resource = resource
+        @user = user
+        @event_created_at = created_at
+      end
+
+      def execute
+        create_event_by_issue if first_weight_event?
+
+        ResourceWeightEvent
+          .new(user: user, issue: resource, weight: resource.weight, created_at: event_created_at)
+          .save
+      end
+
+      private
+
+      def first_weight_event?
+        ResourceWeightEvent.by_issue(resource).none?
+      end
+
+      def create_event_by_issue
+        ResourceWeightEvent
+          .new(user: user, issue: resource, weight: resource.weight, created_at: resource.updated_at)
+          .save
+      end
+    end
+  end
+end

ee/changelogs/unreleased/38096-create-resource-weight-events-table-pd.yml

+---
+title: Track resource weight changes
+merge_request: 21515
+author:
+type: added

ee/spec/models/issue_spec.rb

@@ -116,6 +116,7 @@ describe Issue do
     it { is_expected.to have_many(:vulnerability_links).class_name('Vulnerabilities::IssueLink').inverse_of(:issue) }
     it { is_expected.to have_many(:related_vulnerabilities).through(:vulnerability_links).source(:vulnerability) }
     it { is_expected.to belong_to(:promoted_to_epic).class_name('Epic') }
+    it { is_expected.to have_many(:resource_weight_events) }
 
     describe 'versions.most_recent' do
       it 'returns the most recent version' do

ee/spec/services/ee/issuable/common_system_notes_service_spec.rb

@@ -35,12 +35,40 @@ describe Issuable::CommonSystemNotesService do
 
     subject { described_class.new(project, user).execute(issuable, old_labels: [], is_update: false) }
 
-    it 'creates a system note for weight' do
+    before do
       issuable.weight = 5
       issuable.save
+    end
 
+    it 'creates a system note for weight' do
       expect { subject }.to change { issuable.notes.count }.from(0).to(1)
       expect(issuable.notes.last.note).to match('changed weight')
     end
+
+    context 'when resource weight event tracking is enabled' do
+      before do
+        stub_feature_flags(track_resource_weight_change_events: true)
+      end
+
+      it 'creates a resource weight event' do
+        subject
+
+        note = issuable.notes.last
+        event = issuable.resource_weight_events.last
+
+        expect(event.weight).to eq(5)
+        expect(event.created_at).to eq(note.created_at)
+      end
+    end
+
+    context 'when resource weight event tracking is disabled' do
+      before do
+        stub_feature_flags(track_resource_weight_change_events: false)
+      end
+
+      it 'does not created a resource weight event' do
+        expect { subject }.not_to change { ResourceWeightEvent.count }
+      end
+    end
   end
 end

ee/spec/services/ee/resource_events/change_weight_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe EE::ResourceEvents::ChangeWeightService do
+  let_it_be(:user) { create(:user) }
+
+  let(:issue) { create(:issue, weight: 3) }
+  let(:created_at_time) { Time.new(2019, 1, 1, 12, 30, 48) }
+
+  subject { described_class.new(issue, user, created_at_time).execute }
+
+  before do
+    ResourceWeightEvent.new(issue: issue, user: user).save!
+  end
+
+  it 'creates the expected event record' do
+    expect { subject }.to change { ResourceWeightEvent.count }.by(1)
+
+    record = ResourceWeightEvent.last
+    expect_event_record(record, weight: 3, created_at: created_at_time)
+  end
+
+  context 'when weight is nil' do
+    let(:issue) { create(:issue, weight: nil) }
+
+    it 'creates an event record' do
+      expect { subject }.to change { ResourceWeightEvent.count }.by(1)
+
+      record = ResourceWeightEvent.last
+      expect_event_record(record, weight: nil, created_at: created_at_time)
+    end
+  end
+
+  context 'when there is no existing weight event record' do
+    before do
+      ResourceWeightEvent.delete_all
+    end
+
+    it 'creates the expected event records' do
+      expect { subject }.to change { ResourceWeightEvent.count }.by(2)
+
+      record = ResourceWeightEvent.first
+      expect_event_record(record, weight: 3, created_at: issue.reload.updated_at)
+
+      record = ResourceWeightEvent.last
+      expect_event_record(record, weight: 3, created_at: created_at_time)
+    end
+  end
+
+  def expect_event_record(record, weight:, created_at:)
+    expect(record.issue).to eq(issue)
+    expect(record.user).to eq(user)
+    expect(record.weight).to eq(weight)
+    expect(record.created_at).to eq(created_at)
+  end
+end

spec/factories/resource_weight_events.rb

+# frozen_string_literal: true
+
+FactoryBot.define do
+  factory :resource_weight_event do
+    issue { create(:issue) }
+    user { issue&.author || create(:user) }
+  end
+end

spec/lib/gitlab/import_export/all_models.yml

@@ -8,6 +8,7 @@ issues:
 - milestone
 - notes
 - resource_label_events
+- resource_weight_events
 - sentry_issue
 - label_links
 - labels

spec/models/resource_weight_event_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe ResourceWeightEvent, type: :model do
+  describe 'validations' do
+    it { is_expected.not_to allow_value(nil).for(:user) }
+    it { is_expected.not_to allow_value(nil).for(:issue) }
+    it { is_expected.to allow_value(nil).for(:weight) }
+  end
+
+  describe 'associations' do
+    it { is_expected.to belong_to(:user) }
+    it { is_expected.to belong_to(:issue) }
+  end
+
+  describe '.by_issue' do
+    let_it_be(:user1) { create(:user) }
+    let_it_be(:user2) { create(:user) }
+
+    let_it_be(:issue1) { create(:issue, author: user1) }
+    let_it_be(:issue2) { create(:issue, author: user1) }
+    let_it_be(:issue3) { create(:issue, author: user2) }
+
+    let_it_be(:event1) { create(:resource_weight_event, issue: issue1) }
+    let_it_be(:event2) { create(:resource_weight_event, issue: issue2) }
+    let_it_be(:event3) { create(:resource_weight_event, issue: issue1) }
+
+    it 'returns the expected records for an issue with events' do
+      events = ResourceWeightEvent.by_issue(issue1)
+
+      expect(events).to contain_exactly(event1, event3)
+    end
+
+    it 'returns the expected records for an issue with no events' do
+      events = ResourceWeightEvent.by_issue(issue3)
+
+      expect(events).to be_empty
+    end
+  end
+end