Rinaldi Fonseca rinaldifonseca

Building Rich Domain Models in Rails

Abstract

Domain model is an effective tool for software development. It can be used to express really complex business logic, and to verify and validate the understanding of the domain among stakeholders. Building rich domain models in Rails is hard. Primarily, because of Active Record, which doesn't play well with the domain model approach.

One way to deal with this problem is to use an ORM implementing the data mapper pattern. Unfortunately, there is no production ready ORM doing that for Ruby. DataMapper 2 is going to be the first one.

Another way is to use Active Record just as a persistence mechanism and build a rich domain model on top of it. That's what I'm going to talk about here.

Dynamic Dispatch
Dynamic Method
Ghost Methods
Dynamic Proxies
Blank Slate
Kernel Method
Flattening the Scope (aka Nested Lexical Scopes)
Context Probe
Class Eval (not really a 'spell' more just a demonstration of its usage)
Class Macros

	module Paperclip

	#converts a string into a file for paperclip to save
	# useage
	# self.avatar = Paperclip::string_to_file('bob.png', 'image/png', 'BASE64 here')
	def self.string_to_file(name, type, data)
	image = StringIO.new(data)
	image.class.class_eval { attr_accessor :original_filename, :content_type }
	image.original_filename = name
	image.content_type = type

	# This task will notify Sentry via their API[1] that you have deployed
	# a new release. It uses the release timestamp as the `version`
	# (like 20151113182847) and the git ref as the optional `ref` value.
	#
	# This task requires several environment variables be set (or just
	# hardcode the values in here if you like living on the edge):
	#
	# ENV['SENTRY_API_ENDPOINT'] : API endpoint, https://app.getsentry.com
	# ENV['SENTRY_ORG'] : the organization for this app
	# ENV['SENTRY_PROJECT'] : the project for this app

	module PayPal::SDK
	module REST
	module DataTypes
	Payer.class_eval do
	object_of :merchant_id, String
	end

	class ChargeModel < Base
	object_of :id, String
	object_of :type, String

	package com.trailbehind.downloads;

	import android.util.Log;

	import com.amazonaws.services.s3.AmazonS3Client;
	import com.amazonaws.services.s3.model.GetObjectMetadataRequest;
	import com.amazonaws.services.s3.model.GetObjectRequest;
	import com.amazonaws.services.s3.model.ObjectMetadata;
	import com.amazonaws.services.s3.model.S3Object;
	import com.crashlytics.android.Crashlytics;

	package com.memtrip;

	import java.io.FileNotFoundException;
	import java.io.IOException;
	import java.io.OutputStream;

	import android.content.ContentResolver;
	import android.content.ContentUris;
	import android.content.ContentValues;
	import android.graphics.Bitmap;

	# ListRecurringDetailsResponse#details

	def details
	mapped_attributes = {
	:recurring_detail_reference => "recurringDetailReference",
	:creation_date => "creationDate",
	:variant => "variant",
	:card_holder_name => "card.holderName",
	:card_expiry_month => "card.expiryMonth",
	:card_expiry_year => "card.expiryYear",

	port = 6379
	$redis = Redis.new(:port => port)
	$redis.flushall