7-ways-to-decompose-fat-activerecord-models suggestions for code organization.

You can organize domain (controller, model and view) into separate folders drawers

https://thoughtbot.com/upcase/intermediate-ruby-on-rails https://code.tutsplus.com/articles/a-beginners-guide-to-design-patterns–net-12752

Three basic kind of design pattern:

structural
creational
behavioral

https://www.youtube.com/watch?v=3SGRjUWScRw&feature=youtu.be

Instead of

class Member < ActiveRecord::Base
  has_many :email_addresses
  has_one :primary_email_address, conditions: { primary: true }
end

Use belongs_to on members

class Member < ActiveRecord::Base
  has_many :email_addresses
  belongs_to :primary_email_address, class_name: "EmailAddress", foreign_key: :email_address_id
end

https://thoughtbot.com/blog/handling-associations-on-null-objects

DHH

dhh tips for rails

epipsode 1: do not use comments but method names or constants… follow table of content: method definition should be in same order as they are used in the class (in before callbacks) administered concern define methods on associations. Also use or | to join two arrays

module Account::Administered
  extend ActiveSupport::Concern

  included do
    has_many :administratorships, dependent: :delete_all do
      def grant(person)
        create_or_find person: person
      end

      def revoke(person)
        where(person_id: person.id).destroy_all
      end
    end

    has_many :administrators, through: :administratorships, source: :person
  end

  def all_administrators
    administrators | all_owners
  end

  def administrator_candidates
    people.users.
      where.not(id: administratorships.pluck(:person_id)).
      where.now(id: ownerships.pluck(:person_id)).
      where.not(id: owner_person.id)
  end
end

episode 2: use callbacks to initiate background jobs
episode 3: use globals in request/response cycle. For background jobs you need to pass them as params.
episode 4

Rails Patterns

Pawel Daborwski Patterns are used for benefit of:

isolation: db/payment should be tested separately
readability: class name should tell what given code is doing
extendability: it should be easy to modify by changing in single place
single responsibility: one method for one action

Policy object

It is used to check if someone is allowed to do the action. File name should use _policy suffix. Return only boolean value. Inside method, only call methods on passed objects.

class UsersPolicy
  def initialize(user)
    @user = user
  end
  def admin?
    @user.role == 'admin'
  end
end

Query object

Complex queries should be extracted and tested separatelly. File name could be app/queries/users/list_active_users_query.rb for single query, or app/queries/users_query.rb for multiple #active and #suspended methods. For single query you can use class methods

module Users
  class ListActiveUsersQuery
    def self.call
      User.where(status: 'active').where.not(email: nil)
    end
  end
end

for multiple you can use poro

class UsersQuery
  def initialize(users = User.all)
    @users = users
  end
  def active
    @users.where(active: true)
  end
  def pending
    @users.where(pending: true)
  end
end

and you can chaining query = UsersQuery.new and query.active.pending. You can use https://apidock.com/rails/ActiveRecord/QueryMethods/extending to extend scopes.

Service objects

Always define only one public method: call, perform or process

# app/services/match_posts.rb
def MatchPosts
  def initialize(posts)
    @posts = posts
  end

  def perform
  end
end

You should return object that can be success and hold some data

# app/models/result.rb
class Result
  attr_accessor :message, :data

  # you can return in service like:
  #   return Result.new 'Next task created', next_task: next_task
  # and use in controller:
  #   if result.success? && result.data[:next_task] == task
  def initialize(message, data = {})
    @message = message
    @data = data
  end

  def success?
    true
  end
end

# app/models/error.rb
class Error < Result
  def success?
    false
  end
end

and you can rescue from exceptions:

# app/services/my_service.rb
class MyService
  # Some custom exception if needed
  class ProcessException < Exception
  end

  def initialize(h)
    @user = h[:user]
  end

  def process(posts)
    success_message = do_something posts
    Result.new success_message
  rescue ProcessException => e
    Error.new e.message
  end

  private

  def do_something(posts)
    raise ProcessException, "Error: empty posts" unless posts
    "Done with do_something"
  end
end

# main.rb
require './my_service.rb'

my_service = MyService.new user: 'me'
puts my_service.process(1).success? # true
puts my_service.process(1).message # Done with do_something
puts my_service.process(false).success? # false
puts my_service.process(false).message # empty posts

Observer

We an use observable objects to send notifications implementation in 3 languages It could looks like action as a distance antipattern but if we explicitly add than is it fine. It is called publish/subscriber pattern. It allows you to observe one object and when it’s changed then trigger certain code in other objects that are subscribing the main object.

module ObservableImplementation
  def observers
    @observers ||= []
  end

  def notify_observers(*args)
    observers.each do |observer|
      observer.update(*args)
    end
  end

  def add_observer(object)
    observers << object
  end
end

class Task
  include ObservableImplementation
  attr_accessor :counter
  def initialize
    self.counter = 0
  end

  def tick
    self.counter += 1
    notify_observers(counter)
  end
end

class PutsObserver
  def initialize(observable)
    observable.add_observer self
  end

  def update(counter)
    puts "Count has increased by #{counter}"
  end
end

class DotsObserver
  def initialize(observable)
    observable.add_observer self
  end

  def update(counter)
    puts "." * counter
  end
end

task = Task.new
task.tick
DotsObserver.new(task)
task.tick # ..
PutsObserver.new(task)
task.tick # ...
# Count has increased by 3

In ruby there are https://docs.ruby-lang.org/en/2.2.0/Observable.html where you call changed and notify_observers params (which will set changed to false). You need to call task.add_observer DotsObserver.new.

Interactor

Service object is similar to Command pattern which is implemented in gem https://github.com/collectiveidea/interactor

When does its single purpose, it affects tis given context

context.user = user
context.fail! error: 'Boom'
# .call will swallow exception Interactor::Failure
context.success? # false

Before and after hooks for preparing data. Before hooks are invoked in the order they were defined.

before do
  context.emails_sent = 0
end
after :reload # note that this will not be run if `fail!` is called

Example

# app/interactors/authenticate_user.rb
class AuthenticateUser
  include Interactor

  def call
    if user = User.authenticate(context.email, context.password)
      context.user = user
      context.token = user.secret_token
    else
      context.user = User.new email: context.email
      context.user.errors.add :email, 'wrong email or password'
      context.fail!(message: "authenticate_user.failure")
    end
  end
end

and use in controller like

  result = AuthenticateUser.call(session_params)
  if result.success?
    session[:user_token] = result.token
    redirect_to dashboard_path
  else
    @user = result.user
    render :new
  end

Second type of interactor is Organizer which is used to run other interactors.

class PlaceOrder
  include Interactor::Organizer

  organize CreateOrder, ChargeCard
end

In this case then ChargeCard fails we can use CreateOrder#rollback method to revert changes.

In test, you can stub other method calls and cover 100% of unit interactor tests than write integration or acceptance tests to test wires.

Decorator

It is used to decorate object, ie catch method missing and send to object in initializer on runtime. This is different than subclassing since it happens in run-time.

# app/decorators/user_profile_decorator < SimpleDelegator
class UserProfileDecorator < SimpleDelegator
  def model
    __getobj__
  end
  def name
    "#{model.first_name} #{model.last_name}"
  end
end

usage

user = Struct.new(:first_name, :last_name).new("John", "Doe")
decorator = UserProfileDecorator.new(user)
decorator.first_name # => "John"
decorator.name # => "John Doe"

Gem that supports decorating collections and associations https://github.com/drapergem/draper

Another use case if for dependency injection, for example you have two pdf generators than create graphs and you want to create another pdf that include both graphs. https://www.honeybadger.io/blog/decoupling-ruby-delegation-dependency-injection/

class PrawnWrapper < SimpleDelegator
  def initialize(document: nil)
    document ||= Prawn::Document.new(...)
    super(document)
  end
end

and call others using injection

class OverviewReport < PrawnWrapper
  ...
  def render
    sales = SaleReport.new(..., document: self)
    sales.sales_table
    costs = CostReport.new(..., document: self)
    costs.costs_pie_chart
    ...
  end
end

Facade pattern

page 37

Tips

Builder pattern is usefull to provide flexibility for example https://github.com/rails/rails/blob/main/actionview/lib/action_view/helpers/tags/label.rb#L7

Object Oriented Design Principles And Patterns

Contents

DHH