Common Model mistakes on Rails

1.  Don’t use automatically generated methods

	############
	## WRONG ##
	############
	if course.visible
	# do something
	end
	##############
	## RIGHT ##
	##############
	if course.visible?
	# do something
	end

view raw 01-common-model-mistakes-on-rails.rb hosted with ❤ by GitHub

2. N+1 problems

	#############
	## WRONG ##
	#############
	@homeworks = lesson.homeworks
	- @homeworks.each do |homework|
	%p homework.user.email
	#############
	## RIGHT ##
	#############
	@homeworks = lesson.homeworks.includes(:user)
	- @homeworks.each do |homework|
	%p homework.user.email

view raw 02-common-model-mistakes-on-rails.rb hosted with ❤ by GitHub

3. Don’t use scopes

	############
	## WRONG ##
	############
	def index
	@lessons = Сourse.lessons.order(position: :asc)
	end
	############
	## RIGHT ##
	############
	class Lesson < ActiveRecord::Base
	belongs_to :course
	scope :by_position, -> { order(position: :asc) }
	end
	def index
	@lessons = course.lessons.by_position
	end

view raw 03-common-model-mistakes-on-rails.rb hosted with ❤ by GitHub

4. Don’t know the difference between “after_create” and “after_commit”

• “after_create” might result in invalid data if the ID is used before the transaction is completed.
• Using “Sidekiq” or any other background worker I could always use “after_commit” to ensure the integrity of my data.

5. Always use CRM

	#############
	## WRONG ##
	#############
	Article.all.each { |article| article.delete }
	Article.all.map { |article| article.title }
	Course.all.select { |course| course.created_at < 5.years.ago }.each { |course| course.articles.delete_all }
	#############
	## RIGHT ##
	#############
	Article.delete_all
	Article.pluck(:title)
	old_courses_ids = Course.where(‘created_at < ?’, 5.years.ago’).pluck(:id)
	Article.where(course_id: old_courses_ids).delete_all

view raw 04-common-model-mistakes-on-rails.rb hosted with ❤ by GitHub

6.  Don’t know the difference between “dependent destroy” and “delete_all”

	#############
	## WRONG ##
	#############
	class Article
	validates :body, length: { minimum: 200 }
	end
	articles_data.each do |article_data|
	Article.create(article_data)
	end
	#############
	## RIGHT ##
	#############
	# There are 2 possible solutions
	articles_data.each do |article_data|
	Article.create!(article_data)
	end
	# In this case a developer will be able to see that data he was not expencting to receive will get on the input
	articles_data.each do |article_data|
	article = Article.new(article_data)
	unless article.save
	puts ‘Can not save article’
	#process this situation
	end
	end
	# Give a user a choice.

view raw 05-common-model-mistakes-on-rails.rb hosted with ❤ by GitHub

7.  Don’t set default fields in migrations

	#############
	## WRONG ##
	#############
	class Article
	after_initialize :set_default_status
	def set_default_status
	self.status = ‘pending’
	end
	end
	#############
	## RIGHT ##
	#############
	class MyMigration
	def up
	change_column :articles, status, :string, default: ‘pending’
	end
	def down
	change_column :articles, status, :string
	end
	end

view raw 06-common-model-mistakes-on-rails.rb hosted with ❤ by GitHub

8.  Don’t set constraints in migrations

	#############
	## WRONG ##
	#############
	class MyMigration
	def change
	add_column :profiles, user_id, :integer
	end
	end
	#############
	## RIGHT ##
	#############
	class MyMigration
	def change
	add_column :profiles, user_id, :integer, null: false
	end
	end

view raw 07-common-model-mistakes-on-rails.rb hosted with ❤ by GitHub

9.  Don’t write reverse migrations in migrations
If you are not able to roll back, so what’s point in migrations!?
https://jetruby.com/