Add migration to create missing project features

Relates to: https://gitlab.com/gitlab-org/gitlab/issues/34367

changelogs/unreleased/ab-projects-without-feature.yml

+---
+title: Ensure all Project records have a corresponding ProjectFeature record
+merge_request: 23766
+author:
+type: fixed

db/post_migrate/20200127111840_fix_projects_without_project_feature.rb

+# frozen_string_literal: true
+
+class FixProjectsWithoutProjectFeature < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  BATCH_SIZE = 100_000
+
+  disable_ddl_transaction!
+
+  class Project < ActiveRecord::Base
+    include EachBatch
+  end
+
+  def up
+    queue_background_migration_jobs_by_range_at_intervals(Project, 'FixProjectsWithoutProjectFeature', 2.minutes, batch_size: BATCH_SIZE)
+  end
+
+  def down
+    # no-op
+  end
+end

lib/gitlab/background_migration/fix_projects_without_project_feature.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module BackgroundMigration
+    # Project model for this migration
+    class Project < ActiveRecord::Base
+      include EachBatch
+    end
+
+    ENABLED = 20
+    INSERT_BATCH_SIZE = 10_000
+
+    # This migration creates missing project_features records
+    # for the projects within the given range of ids
+    class FixProjectsWithoutProjectFeature
+      def perform(from_id, to_id)
+        Project.transaction do
+          projects = Project.where(<<~SQL, from_id, to_id)
+            projects.id BETWEEN ? AND ?
+            AND NOT EXISTS (
+              SELECT 1 FROM project_features
+              WHERE project_features.project_id = projects.id
+            )
+          SQL
+
+          projects.each_batch(of: INSERT_BATCH_SIZE) do |batch|
+            insert_missing_records(batch)
+          end
+        end
+      end
+
+      private
+
+      def insert_missing_records(projects)
+        features = projects.map do |project|
+          record = {
+            project_id: project.id,
+            merge_requests_access_level: ENABLED,
+            issues_access_level: ENABLED,
+            wiki_access_level: ENABLED,
+            snippets_access_level: ENABLED,
+            builds_access_level: ENABLED,
+            repository_access_level: ENABLED,
+            pages_access_level: ENABLED,
+            forking_access_level: ENABLED
+          }
+
+          record['created_at'] = record['updated_at'] = Time.now.to_s(:db)
+
+          record
+        end
+
+        Gitlab::Database.bulk_insert(:project_features, features, on_conflict: :do_nothing)
+
+        logger.info(message: "FixProjectsWithoutProjectFeature: created missing project_features for Projects #{projects.map(&:id).join(', ')}")
+      end
+
+      def logger
+        @logger ||= Gitlab::BackgroundMigration::Logger.build
+      end
+    end
+  end
+end

spec/lib/gitlab/background_migration/fix_projects_without_project_feature_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::BackgroundMigration::FixProjectsWithoutProjectFeature, :migration, schema: 2020_01_27_111840 do
+  let(:namespaces) { table(:namespaces) }
+  let(:projects) { table(:projects) }
+  let(:project_features) { table(:project_features) }
+
+  let(:namespace) { namespaces.create(name: 'foo', path: 'foo') }
+  let!(:project) { projects.create!(namespace_id: namespace.id) }
+  let!(:projects_without_feature) { [projects.create!(namespace_id: namespace.id), projects.create!(namespace_id: namespace.id)] }
+
+  before do
+    project_features.create({ project_id: project.id, pages_access_level: 20 })
+  end
+
+  subject { described_class.new.perform(*project_range) }
+
+  def project_feature_records
+    ActiveRecord::Base.connection.select_all('SELECT project_id FROM project_features ORDER BY project_id').map { |e| e['project_id'] }
+  end
+
+  def project_range
+    ActiveRecord::Base.connection.select_one('SELECT MIN(id), MAX(id) FROM projects').values
+  end
+
+  it 'creates a default ProjectFeature for projects without it' do
+    expect { subject }.to change { project_feature_records }.from([project.id]).to([project.id, *projects_without_feature.map(&:id)])
+  end
+
+  it 'sets created_at/updated_at timestamps' do
+    subject
+
+    offenders = ActiveRecord::Base.connection.select_all('SELECT 1 FROM project_features WHERE created_at IS NULL or updated_at IS NULL')
+
+    expect(offenders).to be_empty
+  end
+end