Add merge_trains_enabled to project_ci_cd_settings

Add a migration to create and populate a new merge_trains_enabled
column.

changelogs/unreleased/244831-split-pipelines-for-merged-results-and-merge-train-check-boxes.yml

+---
+title: Add merge trains enabled setting to project ci cd settings
+merge_request: 45834
+author:
+type: other

db/migrate/20201021220101_add_merge_trains_enabled.rb

+# frozen_string_literal: true
+
+class AddMergeTrainsEnabled < ActiveRecord::Migration[6.0]
+  DOWNTIME = false
+
+  def change
+    add_column :project_ci_cd_settings, :merge_trains_enabled, :boolean, default: false, allow_null: false
+  end
+end

db/migrate/20201026200736_seed_merge_trains_enabled.rb

+# frozen_string_literal: true
+
+class SeedMergeTrainsEnabled < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    update_column_in_batches(:project_ci_cd_settings, :merge_trains_enabled, true) do |table, query|
+      query.where(table[:merge_pipelines_enabled].eq(true))
+    end
+  end
+
+  def down
+    # no-op
+  end
+end

db/schema_migrations/20201021220101

+72580665fcb0fca332ede450690902c0a7afb6159feff41df1bc10a3cf6607f2
\ No newline at end of file

db/schema_migrations/20201026200736

+691fe3335de3e072bc5612705c4d16744ff17e334025ddd78eb37309f87441e3
\ No newline at end of file

db/structure.sql

@@ -14817,7 +14817,8 @@ CREATE TABLE project_ci_cd_settings (
     group_runners_enabled boolean DEFAULT true NOT NULL,
     merge_pipelines_enabled boolean,
     default_git_depth integer,
-    forward_deployment_enabled boolean
+    forward_deployment_enabled boolean,
+    merge_trains_enabled boolean DEFAULT false
 );
 
 CREATE SEQUENCE project_ci_cd_settings_id_seq

spec/migrations/seed_merge_trains_enabled_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require Rails.root.join('db', 'migrate', '20201026200736_seed_merge_trains_enabled.rb')
+
+RSpec.describe SeedMergeTrainsEnabled do
+  describe 'migrate' do
+    let(:project_ci_cd_settings) { table(:project_ci_cd_settings) }
+    let(:projects) { table(:projects) }
+    let(:namespaces) { table(:namespaces) }
+
+    context 'when on Gitlab.com' do
+      before do
+        namespace = namespaces.create!(name: 'hello', path: 'hello/')
+        project1 = projects.create!(namespace_id: namespace.id)
+        project2 = projects.create!(namespace_id: namespace.id)
+        project_ci_cd_settings.create!(project_id: project1.id, merge_pipelines_enabled: true)
+        project_ci_cd_settings.create!(project_id: project2.id, merge_pipelines_enabled: false)
+      end
+
+      it 'updates merge_trains_enabled to true for where merge_pipelines_enabled is true' do
+        migrate!
+
+        expect(project_ci_cd_settings.where(merge_trains_enabled: true).count).to be(1)
+      end
+    end
+  end
+end