Add resource label event model and service

This model and service will be used for tracking label changes
on issuable resources. Currently it's not used yet (the reason is
that we don't want to record label events and system notes for labels
at the same time), it will be enabled as part of #48483

app/models/concerns/label_eventable.rb

+# == LabelEventable concern
+#
+# Contains functionality related to objects that support adding/removing events.
+#
+# Used by Issue and MergeRequest.
+#
+
+module LabelEventable
+  extend ActiveSupport::Concern
+
+  included do
+    has_many :resource_label_events
+  end
+end

app/models/issue.rb

@@ -16,6 +16,7 @@ class Issue < ActiveRecord::Base
   include TimeTrackable
   include ThrottledTouch
   include IgnorableColumn
+  include LabelEventable
 
   ignore_column :assignee_id, :branch_name, :deleted_at
 

app/models/merge_request.rb

@@ -11,6 +11,7 @@ class MergeRequest < ActiveRecord::Base
   include EachBatch
   include ThrottledTouch
   include Gitlab::Utils::StrongMemoize
+  include LabelEventable
 
   ignore_column :locked_at,
                 :ref_fetched,

app/models/resource_label_event.rb

+class ResourceLabelEvent < ActiveRecord::Base
+  ISSUABLE_COLUMNS = %i(issue_id merge_request_id).freeze
+
+  belongs_to :user
+  belongs_to :issue
+  belongs_to :merge_request
+  belongs_to :label
+
+  validates :user, presence: true, on: :create
+  validates :label, presence: true, on: :create
+  validate :issuable_id_is_present
+
+  enum action: {
+    add: 1,
+    remove: 2
+  }
+
+  def issuable
+    issue || merge_request
+  end
+
+  private
+
+  def issuable_columns
+    ISSUABLE_COLUMNS
+  end
+
+  def issuable_id_is_present
+    ids = issuable_columns.find_all {|attr| self[attr]}
+
+    if ids.size != 1
+      errors.add(:base, "Exactly one of #{issuable_columns.join(', ')} is required")
+    end
+  end
+end

app/services/resource_label_event_service.rb

+module ResourceLabelEventService
+  extend self
+
+  def change_labels(resource, user, added_labels, removed_labels)
+    label_hash = {
+      resource_column(resource) => resource.id,
+      user_id: user.id,
+      created_at: Time.now
+    }
+
+    labels = added_labels.map do |label|
+      label_hash.merge(label_id: label.id, action: ResourceLabelEvent.actions['add'])
+    end
+    labels += removed_labels.map do |label|
+      label_hash.merge(label_id: label.id, action: ResourceLabelEvent.actions['remove'])
+    end
+
+    Gitlab::Database.bulk_insert(ResourceLabelEvent.table_name, labels)
+  end
+
+  private
+
+  def resource_column(resource)
+    if resource.is_a?(Issue)
+      :issue_id
+    elsif resource.is_a?(MergeRequest)
+      :merge_request_id
+    else
+      raise ArgumentError, "Unknown resource type #{resource.class.name}"
+    end
+  end
+end

db/migrate/20180726172057_create_resource_label_events.rb

+class CreateResourceLabelEvents < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def change
+    create_table :resource_label_events, id: :bigserial do |t|
+      t.integer :action, null: false
+      t.references :issue, null: true, index: true, foreign_key: { on_delete: :cascade }
+      t.references :merge_request, null: true, index: true, foreign_key: { on_delete: :cascade }
+      t.references :label, index: true, foreign_key: { on_delete: :nullify }
+      t.references :user, index: true, foreign_key: { on_delete: :nullify }
+      t.datetime_with_timezone :created_at, null: false
+    end
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20180722103201) do
+ActiveRecord::Schema.define(version: 20180726172057) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -2357,6 +2357,20 @@ ActiveRecord::Schema.define(version: 20180722103201) do
   add_index "remote_mirrors", ["last_successful_update_at"], name: "index_remote_mirrors_on_last_successful_update_at", using: :btree
   add_index "remote_mirrors", ["project_id"], name: "index_remote_mirrors_on_project_id", using: :btree
 
+  create_table "resource_label_events", id: :bigserial, force: :cascade do |t|
+    t.integer "action", null: false
+    t.integer "issue_id"
+    t.integer "merge_request_id"
+    t.integer "label_id"
+    t.integer "user_id"
+    t.datetime_with_timezone "created_at", null: false
+  end
+
+  add_index "resource_label_events", ["issue_id"], name: "index_resource_label_events_on_issue_id", using: :btree
+  add_index "resource_label_events", ["label_id"], name: "index_resource_label_events_on_label_id", using: :btree
+  add_index "resource_label_events", ["merge_request_id"], name: "index_resource_label_events_on_merge_request_id", using: :btree
+  add_index "resource_label_events", ["user_id"], name: "index_resource_label_events_on_user_id", using: :btree
+
   create_table "routes", force: :cascade do |t|
     t.integer "source_id", null: false
     t.string "source_type", null: false
@@ -3017,6 +3031,10 @@ ActiveRecord::Schema.define(version: 20180722103201) do
   add_foreign_key "push_rules", "projects", name: "fk_83b29894de", on_delete: :cascade
   add_foreign_key "releases", "projects", name: "fk_47fe2a0596", on_delete: :cascade
   add_foreign_key "remote_mirrors", "projects", name: "fk_43a9aa4ca8", on_delete: :cascade
+  add_foreign_key "resource_label_events", "issues", on_delete: :cascade
+  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 "saml_providers", "namespaces", column: "group_id", on_delete: :cascade
   add_foreign_key "services", "projects", name: "fk_71cce407f9", on_delete: :cascade
   add_foreign_key "slack_integrations", "services", on_delete: :cascade

spec/factories/resource_label_events.rb

+FactoryBot.define do
+  factory :resource_label_event do
+    user { issue.project.creator }
+    action :add
+    label
+    issue
+  end
+end

spec/lib/gitlab/import_export/all_models.yml

@@ -7,6 +7,7 @@ issues:
 - updated_by
 - milestone
 - notes
+- resource_label_events
 - label_links
 - labels
 - last_edited_by
@@ -79,6 +80,7 @@ merge_requests:
 - updated_by
 - milestone
 - notes
+- resource_label_events
 - label_links
 - labels
 - last_edited_by

spec/models/resource_label_event_spec.rb

+require 'rails_helper'
+
+RSpec.describe ResourceLabelEvent, type: :model do
+  subject { build(:resource_label_event) }
+  let(:issue) { create(:issue) }
+  let(:merge_request) { create(:merge_request) }
+
+  describe 'associations' do
+    it { is_expected.to belong_to(:user) }
+    it { is_expected.to belong_to(:issue) }
+    it { is_expected.to belong_to(:merge_request) }
+    it { is_expected.to belong_to(:label) }
+  end
+
+  describe 'validations' do
+    it { is_expected.to be_valid }
+    it { is_expected.to validate_presence_of(:label) }
+    it { is_expected.to validate_presence_of(:user) }
+
+    describe 'Issuable validation' do
+      it 'is invalid if issue_id and merge_request_id are missing' do
+        subject.attributes = { issue: nil, merge_request: nil }
+
+        expect(subject).to be_invalid
+      end
+
+      it 'is invalid if issue_id and merge_request_id are set' do
+        subject.attributes = { issue: issue, merge_request: merge_request }
+
+        expect(subject).to be_invalid
+      end
+
+      it 'is valid if only issue_id is set' do
+        subject.attributes = { issue: issue, merge_request: nil }
+
+        expect(subject).to be_valid
+      end
+
+      it 'is valid if only merge_request_id is set' do
+        subject.attributes = { merge_request: merge_request, issue: nil }
+
+        expect(subject).to be_valid
+      end
+    end
+  end
+end

spec/services/resource_label_event_service_spec.rb

+require 'spec_helper'
+
+describe ResourceLabelEventService do
+  set(:project)  { create(:project) }
+  set(:author)   { create(:user) }
+  let(:resource) { create(:issue, project: project) }
+
+  describe '.change_labels' do
+    subject { described_class.change_labels(resource, author, added, removed) }
+
+    let(:labels)  { create_list(:label, 2, project: project) }
+    let(:added)   { [labels[0]] }
+    let(:removed) { [labels[1]] }
+
+    it 'creates an event for each label in single query' do
+      expect(Gitlab::Database).to receive(:bulk_insert).once.and_call_original
+      expect { subject }.to change { resource.resource_label_events.count }.from(0).to(2)
+    end
+  end
+end