activemodel-type-with-active-model-dirty-example.rb

# I frequently use ActiveModel::Type to define complex objects in my database. When doing 
# so, there is always a moment when I run into a bug that is caused by me forgetting to 
# support ActiveRecord knowing that the complex type is dirty!

# So here's a quick example that I can reference when I go to make a complex type again 
# that plays nicely *with* ActiveModel::Dirty!

# frozen_string_literal: true

begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler version 1.10 or later is required. Please update your Bundler"
  raise e
end

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  gem "rails", github: "rails/rails"
  gem "sqlite3"
end

require "active_record"
require "minitest/autorun"
require "logger"

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :posts, force: true do |t|
    t.text :metadata, null: false, default: "{}"
  end

  create_table :comments, force: true do |t|
    t.integer :post_id
  end
end


class Metadata
  include ActiveModel::Dirty
  include ActiveModel::Model

  define_attribute_methods :likes
  attr_reader :likes

  def initialize(attributes)
    @likes = attributes[:likes]
  end

  def likes=(num)
    likes_will_change! unless num == @likes
    @likes = num
  end

  def to_h
    { likes: likes }
  end

  class Type < ActiveModel::Type::Value
    def cast(value)
      return value if value.is_a?(Metadata)
      return Metadata.new(value) if value.is_a?(Hash)
      deserialize(value)
    end

    def serialize(value)
      return JSON.dump(value.to_h) if value.respond_to?(:to_h)
      raise "#{value} of type #{value.class} cannot be serialized back into a metadata field"
    end

    def deserialize(value)
      return Metadata.new(JSON.parse(value, symbolize_names: true)) if value.is_a?(String)
      raise "#{value} of type #{value.class} cannot be cast to a Metadata"
    end

    def changed_in_place?(raw_old_value, new_value)
      serialize(new_value) != raw_old_value
    end

    def changed?(old_value, new_value, _new_value_before_type_cast)
      p super
    end
  end
end

class Post < ActiveRecord::Base
  has_many :comments
  attribute :metadata, Metadata::Type.new
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

class DirtyComplexAttributesTest < Minitest::Test
  def test_dirty_complex_objects
    post = Post.create!
    post.metadata.likes = 10
    assert post.metadata_changed?
    post.save
    refute post.metadata_changed?

    loaded_post = Post.find_by(id: post.id)
    assert_equal 10, loaded_post.metadata.likes
    refute loaded_post.metadata_changed?

    # Changing the data makes it dirty
    loaded_post.metadata.likes = 5
    assert loaded_post.metadata_changed?

    # Reloading clears the dirty state
    loaded_post.reload
    refute post.metadata_changed?
    assert loaded_post.metadata.likes = 10

  end
end