50 Most Common Ruby on Rails Developer Mistakes: Controllers

They use instance variables in controllers

Quite often beginners declare all the variables in controllers as instances even if it may not be required. The problem with instance variables is that if you make a mistake, you won’t get the error message. A good practice here is to use one or two instance variables per action. If you need more, group them in Presenter.

	###############
	## WRONG ##
	###############
	classAPI::ArticlesController
	defindex
	@articles=Article.all
	render json: @articles, status: 200
	end
	end
	###############
	## RIGHT ##
	###############
	classAPI::ArticlesController
	defindex
	articles = Article.all
	render json: articles, status: 200
	end
	end

view rawvar.rb hosted with by GitHub

They don’t specify the HTTP response status in API controllers

Designing API you must specify the response status. Thus, the client application is able to know about the previous actions before processing the response body.

	###############
	## WRONG ##
	###############
	classAPI::ArticlesController
	defcreate
	article = Article.new(article_params)
	if article.save
	render json: article
	else
	render json: { errors: article.errors.full_messages }
	end
	end
	end
	###############
	## RIGHT ##
	###############
	classAPI::ArticlesController
	defcreate
	article = Article.new(article_params)
	if article.save
	render json: article, status: 201
	else
	render json: { errors: article.errors.full_messages }, status: 422
	end
	end
	end

view rawdes.rb hosted with by GitHub

Initialize or look for objects without parent connections

The current object’s parent can often be available in the controller. For example, the user should be able to edit only his own objects in the personal account. The range of lessons that can be found is limited by the given course.

Using this simple approach you can make the app more stable and increase its security. What is more important, it will help you to avoid an enormous amount of errors. This approach applies not only to personal accounts but also to nested routes. As soon as you’ve found the parent, look for the child object.

	###############
	## WRONG ##
	###############
	classUsers::CoursesController
	defedit
	@course=Course.find(params[:id])
	end
	end
	classUsers::LessonsController
	defnew
	@lesson=Lesson.new(lesson_params)
	end
	end
	###############
	## RIGHT ##
	###############
	classUsers::CoursesController
	defedit
	@course= current_user.courses.find(params[:id])
	end
	end
	classUsers::LessonsController
	defnew
	course = current_user.courses.find(params[:course_id])
	@lesson= course.lessons.build(lesson_params)
	end
	end

view rawpar.rb hosted with by GitHub

They use instance variables in partials

The problem with using instance variables in partials is that as soon as the project starts growing everything turns into a mess. It will be really hard to tell which variable came from where. Thus, supporting all of the dependencies becomes impossible.

	###############
	## WRONG ##
	###############
	= render 'form'
	# _form.html.haml:
	= simple_form_for [:users, @course] do |f|
	-# some form
	###############
	## RIGHT ##
	###############
	= render 'form', course: course
	# _form.html.haml:
	= simple_form_for [:users, course] do |f|
	-# some form

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