Gist for Let's Build A Gem With Rails

01_Initial command

bundle gem change_ledger --coc --mit --exe --test=rspec --ci=github --linter=standard

02_Add Rails as a dependency

# in change_ledger.gemspec

spec.add_dependency "rails", ">= 7.0.0"

03_Add RSpec Rails as a dependency

# in change_ledger.gemspec

add_development_dependency "rspec-rails", "~> 3.1.0"

04_First spec

#spec/lib/change_ledger/ledger_spec.rb

require "time" 
module ChangeLedger
  Dummy = Data.define(:id, :name) do
    def to_global_id = "dummy_#{id}"
    def attributes = {"id" => id, "name" => name}
  end

  RSpec.describe Ledger do
    it "creates rows" do
      instance = Dummy.new(id: 3, name: "Noel")
      time = Time.parse("May 5, 2024 2:30 pm")
      travel_to(time) do
        result = Ledger.entry(instance, :name)
        expect(result).to have_attributes(
          id: a_truthy_value,
          global_id: "dummy_3",
          target: "name",
          value: "Noel",
          changed_at: time
        )
      end
    end
  end

05_First code

# lib/change_ledger/ledger.rb

module ChangeLedger
  class Ledger

  end
end

06_Require code

# in lib/change_ledger.rb

require_relative "change_ledger/ledger"

07_add zeitwerk

# change_ledger.gemspec

add_dependency "zeitwerk"

08_really add zeitwerk

# lib/change_ledger.rb
require "zeitwerk"
loader = Zeitwerk::Loader.for_gem(warn_on_extra_files: false)
loader.setup

09_add active support

# spec/spec_helper.rb

# at the top of the file

require "active_support/all"
require "active_support/testing/time_helpers"
require "active_record"



# in the config block

config.include ActiveSupport::Testing::TimeHelpers

10_business logic

# lib/change_ledger/ledger.rb

module ChangeLedger
  class Ledger < ActiveRecord::Base
    def self.entry(instance, target)
      create(
        global_id: instance.to_global_id,
        target: target.to_s,
        value: instance.attributes[target.to_s],
        changed_at: Time.current
      )
    end
  end
end

11_stubbed test

#    spec/lib/change_ledger/ledger_spec.rb
   
   it "creates rows" do
      instance = Dummy.new(id: 3, name: "Noel")
      time = Time.parse("May 5, 2024 2:30 pm")
      allow(Ledger).to receive(:create)
      travel_to(time) do
        result = Ledger.entry(instance, :name)
        expect(Ledger).to have_received(:create).with(
          global_id: "dummy_3",
          target: :name,
          value: "Noel",
          changed_at: time
        )
      end
    end

12_add sqlite as a dev dependency

# change_ledger.gemspec
spec.add_development_dependency "sqlite3", "~> 1.7"

13_add sqlite to the spec helper

# spec/spec_helper.rb
# bottom of file

ActiveRecord::Base.establish_connection(
  adapter: "sqlite3", 
  database: ":memory:"
)
load("#{__dir__}/schema.rb")

14_add schema

# spec/schema.rb

ActiveRecord::Schema.define do
  self.verbose = false
  create_table :ledgers, force: true do |t|
    t.string :global_id, null: false
    t.string :target, null: false
    t.string :value, null: false
    t.datetime :changed_at, null: false
    t.timestamps
  end
end

15_reinstate test

# spec/lib/change_ledger/ledger_spec.rb

RSpec.describe Ledger do
    it "creates rows" do
      instance = Dummy.new(id: 3, name: "Noel")
      time = Time.parse("May 5, 2024 2:30 pm")
      travel_to(time) do
        result = Ledger.entry(instance, :name)
        expect(result).to have_attributes(
          id: a_truthy_value,
          global_id: "dummy_3",
          target: "name",
          value: "Noel",
          changed_at: time
        )
      end
    end
  end

16_Add combustion gem

# change_ledger.gemspec
spec.add_development_dependency "combustion"

17_add combustion to spec helper

# spec/spec_helper.rb

# remove the things added in the last step

# top of file
require "combustion"

Combustion.initialize! :all

18_Sample railtie

# this would go in lib/change_ledger/railtie.rb, but we're not acutally going to do it

module ChangeLedger
  class Railtie < Rails::Railtie
    initializer "change_ledger.configure" do |app|
      if File.exist?(".change_ledger.yml")
        Configuration.from_file(".change_ledger.yml")
      end
    end
  end
end

19_add generator

# lib/generators/change_ledger/migration_generator.rb

require "rails/generators"
require "rails/generators/active_record"

module ChangeLedger
  class MigrationGenerator < Rails::Generators::Base
    include ActiveRecord::Generators::Migration
    source_root File.expand_path("templates", __dir__)

    def copy_migration
      migration_template "migration.rb.erb", "db/migrate/add_ledgers.rb"
    end
  end
end

20_add template

# lib/generators/change_ledger/templates/migration.rb.erb

# frozen_string_literal: true

class AddLedgerTable < ActiveRecord::Migration<%= "[#{Rails::VERSION::MAJOR}.#{Rails::VERSION::MINOR}]" %>
  def change
    create_table :ledgers do |t|
      t.string :global_id
      t.string :target
      t.string :value
      t.datetime :changed_at
      t.timestamps null: false
    end
  end

  add_index :ledgers, :target
  add_index :ledgers, :global_id
end

21_using the generator

# in the Gemfile of another Rails app


gem "change_ledger", path: "../change_ledger"

# in the routes file

# then from the command line

$ rails generate help

$ rails generate change_ledger:migration

22_add an engine

 # lib/change_ledger/engine.rb
 
 module ChangeLedger
  class Engine < ::Rails::Engine
    isolate_namespace ChangeLedger
  end
end

ChangeLedger::Engine.routes.draw do
  root "home#show"
end

23_add a controller

# lib/change_ledger/home_controller.rb

module ChangeLedger
  class HomeController < ActionController::Base
    def show
      render inline: "Hi"
    end
  end
end

24_mounting the engine

# config/routes.rb of using Rails app

mount ChangeLedger::Engine => "/ledger"

25_Appraisals file

appraise "rails-7" do
  gem "rails", "~> 7.0.0"
end

appraise "rails-71" do
  gem "rails", "~> 7.1.0"
end

26_Using appraisal

$ bundle exec appraisal install

# then

$ bundle exec appraisal rspec