Create ActiveRecordModel and table for Merge Train feature

This database table and AR model is going to be used for
the merge train feature.

db/migrate/20190418182545_create_merge_request_trains_table.rb

+# frozen_string_literal: true
+
+class CreateMergeRequestTrainsTable < ActiveRecord::Migration[5.1]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def change
+    create_table :merge_trains, id: :bigserial do |t|
+      t.references :merge_request, foreign_key: { on_delete: :cascade }, type: :integer, index: false, null: false
+      t.references :user, foreign_key: { on_delete: :cascade }, type: :integer, null: false
+      t.references :pipeline, foreign_key: { to_table: :ci_pipelines, on_delete: :nullify }, type: :integer
+      t.timestamps_with_timezone null: false
+
+      t.index [:merge_request_id], unique: true
+    end
+  end
+end

db/schema.rb

@@ -1947,6 +1947,17 @@ ActiveRecord::Schema.define(version: 20190426180107) do
     t.index ["merge_request_id"], name: "index_merge_requests_closing_issues_on_merge_request_id", using: :btree
   end
 
+  create_table "merge_trains", force: :cascade do |t|
+    t.integer "merge_request_id", null: false
+    t.integer "user_id", null: false
+    t.integer "pipeline_id"
+    t.datetime_with_timezone "created_at", null: false
+    t.datetime_with_timezone "updated_at", null: false
+    t.index ["merge_request_id"], name: "index_merge_trains_on_merge_request_id", unique: true, using: :btree
+    t.index ["pipeline_id"], name: "index_merge_trains_on_pipeline_id", using: :btree
+    t.index ["user_id"], name: "index_merge_trains_on_user_id", using: :btree
+  end
+
   create_table "milestones", id: :serial, force: :cascade do |t|
     t.string "title", null: false
     t.integer "project_id"
@@ -3636,6 +3647,9 @@ ActiveRecord::Schema.define(version: 20190426180107) do
   add_foreign_key "merge_requests", "users", column: "updated_by_id", name: "fk_641731faff", on_delete: :nullify
   add_foreign_key "merge_requests_closing_issues", "issues", on_delete: :cascade
   add_foreign_key "merge_requests_closing_issues", "merge_requests", on_delete: :cascade
+  add_foreign_key "merge_trains", "ci_pipelines", column: "pipeline_id", on_delete: :nullify
+  add_foreign_key "merge_trains", "merge_requests", on_delete: :cascade
+  add_foreign_key "merge_trains", "users", on_delete: :cascade
   add_foreign_key "milestones", "namespaces", column: "group_id", name: "fk_95650a40d4", on_delete: :cascade
   add_foreign_key "milestones", "projects", name: "fk_9bd0a0c791", on_delete: :cascade
   add_foreign_key "namespace_statistics", "namespaces", on_delete: :cascade

ee/app/models/ee/merge_request.rb

@@ -21,6 +21,7 @@ module EE
       has_many :approver_groups, as: :target, dependent: :delete_all # rubocop:disable Cop/ActiveRecordDependent
       has_many :approval_rules, class_name: 'ApprovalMergeRequestRule', inverse_of: :merge_request
       has_many :draft_notes
+      has_one :merge_train
 
       validate :validate_approval_rule_source
 
@@ -53,6 +54,18 @@ module EE
       super
     end
 
+    def get_on_train!(user)
+      create_merge_train!(user: user)
+    end
+
+    def get_off_train!
+      merge_train.destroy!
+    end
+
+    def on_train?
+      merge_train.present?
+    end
+
     def allows_multiple_assignees?
       project.multiple_mr_assignees_enabled? &&
         project.feature_available?(:multiple_merge_request_assignees)

ee/app/models/ee/project.rb

@@ -61,6 +61,7 @@ module EE
       accepts_nested_attributes_for :software_license_policies, allow_destroy: true
       has_many :packages, class_name: 'Packages::Package'
       has_many :package_files, through: :packages, class_name: 'Packages::PackageFile'
+      has_many :merge_trains
 
       has_many :sourced_pipelines, class_name: 'Ci::Sources::Pipeline', foreign_key: :source_project_id
 

ee/app/models/merge_train.rb

+# frozen_string_literal: true
+
+class MergeTrain < ApplicationRecord
+  belongs_to :merge_request
+  belongs_to :user
+  belongs_to :pipeline, class_name: 'Ci::Pipeline'
+
+  class << self
+    def all_in_train(merge_request)
+      joined_merge_requests(merge_request).order('merge_trains.id ASC')
+    end
+
+    def first_in_train(merge_request)
+      all_in_train(merge_request).first
+    end
+
+    def joined_merge_requests(merge_request)
+      MergeRequest.joins(:merge_train)
+        .where('merge_requests.target_project_id = ?', merge_request.target_project_id)
+        .where('merge_requests.target_branch = ?', merge_request.target_branch)
+    end
+  end
+
+  def all_next
+    self.class.all_in_train(merge_request).where('merge_trains.id > ?', id)
+  end
+
+  def first_in_train?
+    !follower_in_train?
+  end
+
+  def follower_in_train?
+    self.class.all_in_train(merge_request).where('merge_trains.id < ?', id).exists?
+  end
+end

ee/changelogs/unreleased/create-merge-request-pipeline-on-chained-merge-ref.yml

+---
+title: Create ActiveRecordModel and table for Merge Train feature
+merge_request: 11204
+author:
+type: added

ee/spec/factories/merge_requests.rb

@@ -8,6 +8,16 @@ FactoryBot.modify do
       end
     end
 
+    trait :on_train do
+      transient do
+        train_creator { author }
+      end
+
+      after :create do |merge_request, evaluator|
+        merge_request.get_on_train!(evaluator.train_creator)
+      end
+    end
+
     transient do
       approval_groups []
       approval_users []

ee/spec/factories/merge_trains.rb

+# frozen_string_literal: true
+
+FactoryBot.define do
+  factory :merge_train do
+    merge_request
+    user
+    pipeline factory: :ci_pipeline
+  end
+end

ee/spec/lib/gitlab/import_export/all_models.yml

@@ -14,6 +14,7 @@ merge_requests:
 - approver_groups
 - approved_by_users
 - draft_notes
+- merge_train
 ci_pipelines:
 - source_pipeline
 - source_bridge
@@ -81,6 +82,7 @@ project:
 - webide_pipelines
 - reviews
 - incident_management_setting
+- merge_trains
 prometheus_metrics:
 - project
 - prometheus_alerts
@@ -103,3 +105,6 @@ reviews:
 - notes
 incident_management_setting:
 - project
+merge_trains:
+- project
+- merge_request

ee/spec/models/merge_request_spec.rb

@@ -15,6 +15,7 @@ describe MergeRequest do
     it { is_expected.to have_many(:approver_users).through(:approvers) }
     it { is_expected.to have_many(:approver_groups).dependent(:delete_all) }
     it { is_expected.to have_many(:approved_by_users) }
+    it { is_expected.to have_one(:merge_train) }
   end
 
   it_behaves_like 'an editable mentionable with EE-specific mentions' do
@@ -948,4 +949,64 @@ describe MergeRequest do
       it_behaves_like 'merge pipelines project option is disabled'
     end
   end
+
+  describe '#get_on_train!' do
+    subject { merge_request.get_on_train!(user) }
+
+    let(:user) { create(:user) }
+
+    it 'gets on the train' do
+      expect { subject }.to change { MergeTrain.count }.by(1)
+    end
+
+    context 'when the merge request is already on a merge train' do
+      before do
+        merge_request.get_on_train!(user)
+      end
+
+      it 'raises an exception' do
+        expect { merge_request.get_on_train!(user) }.to raise_exception(ActiveRecord::RecordNotUnique)
+      end
+    end
+  end
+
+  describe '#get_off_train!' do
+    subject { merge_request.get_off_train! }
+
+    let!(:merge_request) do
+      create(:merge_request, :on_train, source_project: project, target_project: project)
+    end
+
+    it 'gets off from the train' do
+      expect { subject }.to change { MergeTrain.count }.by(-1)
+    end
+
+    context 'when the merge request is not on a merge train yet' do
+      let(:merge_request) { create(:merge_request, source_project: project, target_project: project) }
+
+      it 'raises an exception' do
+        expect { subject }.to raise_exception(NoMethodError)
+      end
+    end
+  end
+
+  describe '#on_train?' do
+    subject { merge_request.on_train? }
+
+    context 'when the merge request is on a merge train' do
+      let(:merge_request) do
+        create(:merge_request, :on_train, source_project: project, target_project: project)
+      end
+
+      it { is_expected.to be_truthy }
+    end
+
+    context 'when the merge request is not on a merge train' do
+      let(:merge_request) do
+        create(:merge_request, source_project: project, target_project: project)
+      end
+
+      it { is_expected.to be_falsy }
+    end
+  end
 end

ee/spec/models/merge_train_spec.rb

+# frozen_string_literal: true
+
+require "spec_helper"
+
+describe MergeTrain do
+  include ProjectForksHelper
+
+  set(:project) { create(:project, :repository) }
+
+  it { is_expected.to belong_to(:merge_request) }
+  it { is_expected.to belong_to(:user) }
+  it { is_expected.to belong_to(:pipeline) }
+
+  describe '.all_in_train' do
+    subject { described_class.all_in_train(merge_request) }
+
+    let!(:merge_request) { create_merge_request_on_train }
+
+    it 'returns the merge request' do
+      is_expected.to eq([merge_request])
+    end
+
+    context 'when the other merge request is on the merge train' do
+      let!(:merge_request_2) { create_merge_request_on_train(source_branch: 'improve/awesome') }
+
+      it 'returns the merge request' do
+        is_expected.to eq([merge_request, merge_request_2])
+      end
+    end
+
+    context 'when the merge request is not on merge train' do
+      let(:merge_request) { create(:merge_request) }
+
+      it 'returns empty array' do
+        is_expected.to be_empty
+      end
+    end
+  end
+
+  describe '.first_in_train' do
+    subject { described_class.first_in_train(merge_request) }
+
+    let!(:merge_request) { create_merge_request_on_train }
+
+    it 'returns the merge request' do
+      is_expected.to eq(merge_request)
+    end
+
+    context 'when the other merge request is on the merge train' do
+      let!(:merge_request_2) { create_merge_request_on_train(source_branch: 'improve/awesome') }
+
+      it 'returns the merge request' do
+        is_expected.to eq(merge_request)
+      end
+    end
+
+    context 'when the merge request is not on merge train' do
+      let(:merge_request) { create(:merge_request) }
+
+      it 'returns empty array' do
+        is_expected.to be_nil
+      end
+    end
+  end
+
+  describe '#all_next' do
+    subject { merge_train.all_next }
+
+    let(:merge_train) { merge_request.merge_train }
+    let!(:merge_request) { create_merge_request_on_train }
+
+    it 'returns nil' do
+      is_expected.to be_empty
+    end
+
+    context 'when the other merge request is on the merge train' do
+      let!(:merge_request_2) { create_merge_request_on_train(source_branch: 'improve/awesome') }
+
+      it 'returns the next merge requests' do
+        is_expected.to eq([merge_request_2])
+      end
+    end
+  end
+
+  describe '#first_in_train?' do
+    subject { merge_train.first_in_train? }
+
+    let(:merge_train) { merge_request.merge_train }
+    let!(:merge_request) { create_merge_request_on_train }
+
+    it { is_expected.to be_truthy }
+
+    context 'when the other merge request is on the merge train' do
+      let(:merge_train) { merge_request_2.merge_train }
+      let!(:merge_request_2) { create_merge_request_on_train(source_branch: 'improve/awesome') }
+
+      it { is_expected.to be_falsy }
+    end
+  end
+
+  describe '#follower_in_train?' do
+    subject { merge_train.follower_in_train? }
+
+    let(:merge_train) { merge_request.merge_train }
+    let!(:merge_request) { create_merge_request_on_train }
+
+    it { is_expected.to be_falsy }
+
+    context 'when the other merge request is on the merge train' do
+      let(:merge_train) { merge_request_2.merge_train }
+      let!(:merge_request_2) { create_merge_request_on_train(source_branch: 'improve/awesome') }
+
+      it { is_expected.to be_truthy }
+    end
+  end
+
+  def create_merge_request_on_train(target_project: project, target_branch: 'master', source_project: project, source_branch: 'feature')
+    create(:merge_request,
+      :on_train,
+      target_branch: target_branch,
+      target_project: target_project,
+      source_branch: source_branch,
+      source_project: source_project)
+  end
+end