ActiveRecord - Outside Rails (microservice example)

20180711220702_create_foos.rb

class CreateFoo < ActiveRecord::Migration[5.0]
  def change
    create_table(:foos, force: true) do |t|
      t.text     :message, null: false
      t.datetime :created_at,  null: false
    end
  end
end

db.rake

require 'active_record'
require 'erb'

namespace :db do
  env    = ENV['MICROSERVICE_ENV']
  config = File
    .read('config/database.yml')
    .then(&ERB.method(:new))
    .then(&:result)
    .then(&YAML.method(:load))
    .dig(env)

  desc 'Create the database'
  task :create do
    admin_config = config.merge('database' => 'postgres', 'schema_search_path' => 'public')
    ActiveRecord::Base.establish_connection(admin_config)
    ActiveRecord::Base.connection.create_database(config['database'])
    puts 'Database created.'
  end

  desc 'Migrate the database'
  task :migrate do
    ActiveRecord::Base.establish_connection(config)
    ActiveRecord::Base.connection.migration_context.migrate
    Rake::Task['db:schema'].invoke
    puts 'Database migrated.'
  end

  desc 'Migrate the database'
  task :rollback do
    ActiveRecord::Base.establish_connection(config)
    ActiveRecord::Base.connection.migration_context.rollback
    Rake::Task['db:schema'].invoke
    puts 'Last migration has been reverted.'
  end

  desc 'Drop the database'
  task :drop do
    admin_config = config.merge('database' => 'postgres', 'schema_search_path' => 'public')
    ActiveRecord::Base.establish_connection(admin_config)
    ActiveRecord::Base.connection.drop_database(config['database'])
    puts 'Database deleted.'
  end

  desc '[Reset the database'
  task reset: %i[drop create migrate]

  desc 'Create a db/schema.rb file that is portable against any DB supported by AR'
  task :schema do
    require 'active_record/schema_dumper'
    ActiveRecord::Base.establish_connection(config)
    File.open('db/schema.rb', 'w:utf-8') do |file|
      ActiveRecord::SchemaDumper.dump(ActiveRecord::Base.connection, file)
    end
  end
end

namespace :g do
  desc 'Generate migration'
  task :migration do
    name       = ARGV[1] || raise('Specify name: rake g:migration your_migration')
    timestamp  = Time.now.strftime("%Y%m%d%H%M%S")
    path       = File.expand_path("../../../db/migrate/#{timestamp}_#{name}.rb", __FILE__)
    klass_name = name.split('_').map(&:capitalize).join

    File.open(path, 'w') do |file|
      file.write <<~EOF
        class #{klass_name} < ActiveRecord::Migration[5.0]
          def change
          end
        end
      EOF
    end

    puts "Migration #{path} created"
    abort
  end
end

Rakefile

#!/usr/bin/env rake

require_relative './config/setup'

Dir['lib/tasks/**/*.rake'].each { |path| load path }

setup.rb

# Require external gems
require 'bundler/setup'

ROOT_DIR   = File.expand_path("../", File.dirname(__FILE__)).freeze
CONFIG_DIR = File.join(ROOT_DIR, 'config').freeze

# Require environment & server config files
%w[environment server].each { |path| require File.join(CONFIG_DIR, path) }

Microservice::Env = Microservice::Config::Environment

# Microservice setup
module Microservice
  module Config
    module Setup
      FILES = {
        lib: Dir['lib/**/*.rb'].map { |path| path.gsub(/lib\//, '') },
        initializers: Dir['config/initializers/**/*.rb']
      }.freeze

      module_function

      def apply
        update_load_path
        require_bundled_gems
        require_initializers
        require_inner_lib_files
        initialize_database
      end

      def update_load_path
        lib_dir = File.join(ROOT_DIR, 'lib')
        $LOAD_PATH.push(lib_dir) unless $LOAD_PATH.include?(lib_dir)
      end

      def require_bundled_gems
        Bundler.require(:default, Microservice::Env.name)
      end

      def require_inner_lib_files
        proto_files, other_files = FILES[:lib].partition { |path| path =~ /_pb.rb\z/ }
        require_multiple(proto_files)
        require_multiple(other_files)
      end

      def require_multiple(path_array)
        path_array.each { |path| require path }
      end

      def require_initializers
        FILES[:initializers].each { |path| require ['.', path].join('/') }
      end

      def initialize_database
        ActiveRecord::Base.establish_connection(database_config)
      end

      def database_config
        @database_config ||= File
          .read('config/database.yml')
          .then(&ERB.method(:new))
          .then(&:result)
          .then(&YAML.method(:load))
          .dig(Microservice::Env.name)
      end
    end
  end
end

Microservice::Config::Setup.apply