Getting Started with Rails — Ruby on Rails Guides (2024)

1 Guide Assumptions

This guide is designed for beginners who want to get started with creating a Railsapplication from scratch. It does not assume that you have any prior experiencewith Rails.

Rails is a web application framework running on the Ruby programming language.If you have no prior experience with Ruby, you will find a very steep learningcurve diving straight into Rails. There are several curated lists of online resourcesfor learning Ruby:

• Official Ruby Programming Language website
• List of Free Programming Books

Be aware that some resources, while still excellent, cover older versions ofRuby, and may not include some syntax that you will see in day-to-daydevelopment with Rails.

2 What is Rails?

Rails is a web application development framework written in the Ruby programming language.It is designed to make programming web applications easier by making assumptionsabout what every developer needs to get started. It allows you to write lesscode while accomplishing more than many other languages and frameworks.Experienced Rails developers also report that it makes web applicationdevelopment more fun.

Rails is opinionated software. It makes the assumption that there is a "best"way to do things, and it's designed to encourage that way - and in some cases todiscourage alternatives. If you learn "The Rails Way" you'll probably discover atremendous increase in productivity. If you persist in bringing old habits fromother languages to your Rails development, and trying to use patterns youlearned elsewhere, you may have a less happy experience.

The Rails philosophy includes two major guiding principles:

• Don't Repeat Yourself: DRY is a principle of software development whichstates that "Every piece of knowledge must have a single, unambiguous, authoritativerepresentation within a system". By not writing the same information over and overagain, our code is more maintainable, more extensible, and less buggy.
• Convention Over Configuration: Rails has opinions about the best way to do manythings in a web application, and defaults to this set of conventions, rather thanrequire that you specify minutiae through endless configuration files.

3 Creating a New Rails Project

The best way to read this guide is to follow it step by step. All steps areessential to run this example application and no additional code or steps areneeded.

By following along with this guide, you'll create a Rails project calledblog, a (very) simple weblog. Before you can start building the application,you need to make sure that you have Rails itself installed.

The examples below use $ to represent your terminal prompt in a UNIX-like OS,though it may have been customized to appear differently. If you are using Windows,your prompt will look something like C:\source_code>.

3.1 Installing Rails

Before you install Rails, you should check to make sure that your system has theproper prerequisites installed. These include:

• Ruby
• SQLite3

3.1.1 Installing Ruby

Open up a command line prompt. On macOS open Terminal.app; on Windows choose"Run" from your Start menu and type cmd.exe. Any commands prefaced with adollar sign $ should be run in the command line. Verify that you have acurrent version of Ruby installed:

$ ruby --versionruby 2.7.0

Rails requires Ruby version 2.7.0 or later. It is preferred to use the latest Ruby version.If the version number returned is less than that number (such as 2.3.7, or 1.8.7),you'll need to install a fresh copy of Ruby.

To install Rails on Windows, you'll first need to install Ruby Installer.

For more installation methods for most Operating Systems take a look atruby-lang.org.

3.1.2 Installing SQLite3

You will also need an installation of the SQLite3 database.Many popular UNIX-like OSes ship with an acceptable version of SQLite3.Others can find installation instructions at the SQLite3 website.

Verify that it is correctly installed and in your load PATH:

$ sqlite3 --version

The program should report its version.

3.1.3 Installing Rails

To install Rails, use the gem install command provided by RubyGems:

$ gem install rails

To verify that you have everything installed correctly, you should be able torun the following in a new terminal:

$ rails --versionRails 7.1.0

If it says something like "Rails 7.1.0", you are ready to continue.

3.2 Creating the Blog Application

Rails comes with a number of scripts called generators that are designed to makeyour development life easier by creating everything that's necessary to startworking on a particular task. One of these is the new application generator,which will provide you with the foundation of a fresh Rails application so thatyou don't have to write it yourself.

To use this generator, open a terminal, navigate to a directory where you haverights to create files, and run:

$ rails new blog

This will create a Rails application called Blog in a blog directory andinstall the gem dependencies that are already mentioned in Gemfile usingbundle install.

You can see all of the command line options that the Rails applicationgenerator accepts by running rails new --help.

After you create the blog application, switch to its folder:

$ cd blog

The blog directory will have a number of generated files and folders that makeup the structure of a Rails application. Most of the work in this tutorial willhappen in the app folder, but here's a basic rundown on the function of eachof the files and folders that Rails creates by default:

4 Hello, Rails!

To begin with, let's get some text up on screen quickly. To do this, you need toget your Rails application server running.

4.1 Starting Up the Web Server

You actually have a functional Rails application already. To see it, you need tostart a web server on your development machine. You can do this by running thefollowing command in the blog directory:

$ bin/rails server

If you are using Windows, you have to pass the scripts under the binfolder directly to the Ruby interpreter e.g. ruby bin\rails server.

JavaScript asset compression requires youhave a JavaScript runtime available on your system, in the absenceof a runtime you will see an execjs error during asset compression.Usually macOS and Windows come with a JavaScript runtime installed.therubyrhino is the recommended runtime for JRuby users and is added bydefault to the Gemfile in apps generated under JRuby. You can investigateall the supported runtimes at ExecJS.

This will start up Puma, a web server distributed with Rails by default. To seeyour application in action, open a browser window and navigate tohttp://localhost:3000. You should see the Rails default information page:

When you want to stop the web server, hit Ctrl+C in the terminal window whereit's running. In the development environment, Rails does not generallyrequire you to restart the server; changes you make in files will beautomatically picked up by the server.

The Rails startup page is the smoke test for a new Railsapplication: it makes sure that you have your software configured correctlyenough to serve a page.

4.2 Say "Hello", Rails

To get Rails saying "Hello", you need to create at minimum a route, acontroller with an action, and a view. A route maps a request to acontroller action. A controller action performs the necessary work to handle therequest, and prepares any data for the view. A view displays data in a desiredformat.

In terms of implementation: Routes are rules written in a Ruby DSL(Domain-Specific Language).Controllers are Ruby classes, and their public methods are actions. And viewsare templates, usually written in a mixture of HTML and Ruby.

Let's start by adding a route to our routes file, config/routes.rb, at thetop of the Rails.application.routes.draw block:

Rails.application.routes.draw do get "/articles", to: "articles#index" # For details on the DSL available within this file, see https://guides.rubyonrails.org/routing.htmlend

The route above declares that GET /articles requests are mapped to the indexaction of ArticlesController.

To create ArticlesController and its index action, we'll run the controllergenerator (with the --skip-routes option because we already have anappropriate route):

$ bin/rails generate controller Articles index --skip-routes

Rails will create several files for you:

create app/controllers/articles_controller.rbinvoke erbcreate app/views/articlescreate app/views/articles/index.html.erbinvoke test_unitcreate test/controllers/articles_controller_test.rbinvoke helpercreate app/helpers/articles_helper.rbinvoke test_unit

The most important of these is the controller file,app/controllers/articles_controller.rb. Let's take a look at it:

class ArticlesController < ApplicationController def index endend

The index action is empty. When an action does not explicitly render a view(or otherwise trigger an HTTP response), Rails will automatically render a viewthat matches the name of the controller and action. Convention OverConfiguration! Views are located in the app/views directory. So the indexaction will render app/views/articles/index.html.erb by default.

Let's open app/views/articles/index.html.erb, and replace its contents with:

<h1>Hello, Rails!</h1>

If you previously stopped the web server to run the controller generator,restart it with bin/rails server. Now visit http://localhost:3000/articles,and see our text displayed!

4.3 Setting the Application Home Page

At the moment, http://localhost:3000 still displays a page with the Ruby on Rails logo.Let's display our "Hello, Rails!" text at http://localhost:3000 as well. To doso, we will add a route that maps the root path of our application to theappropriate controller and action.

Let's open config/routes.rb, and add the following root route to the top ofthe Rails.application.routes.draw block:

Rails.application.routes.draw do root "articles#index" get "/articles", to: "articles#index"end

Now we can see our "Hello, Rails!" text when we visit http://localhost:3000,confirming that the root route is also mapped to the index action ofArticlesController.

5 Autoloading

Rails applications do not use require to load application code.

You may have noticed that ArticlesController inherits from ApplicationController, but app/controllers/articles_controller.rb does not have anything like

require "application_controller" # DON'T DO THIS.

Application classes and modules are available everywhere, you do not need and should not load anything under app with require. This feature is called autoloading, and you can learn more about it in Autoloading and Reloading Constants.

You only need require calls for two use cases:

• To load files under the lib directory.
• To load gem dependencies that have require: false in the Gemfile.

6 MVC and You

So far, we've discussed routes, controllers, actions, and views. All of theseare typical pieces of a web application that follows the MVC (Model-View-Controller) pattern.MVC is a design pattern that divides the responsibilities of an application tomake it easier to reason about. Rails follows this design pattern by convention.

Since we have a controller and a view to work with, let's generate the nextpiece: a model.

6.1 Generating a Model

A model is a Ruby class that is used to represent data. Additionally, modelscan interact with the application's database through a feature of Rails calledActive Record.

To define a model, we will use the model generator:

$ bin/rails generate model Article title:string body:text

Model names are singular, because an instantiated model represents asingle data record. To help remember this convention, think of how you wouldcall the model's constructor: we want to write Article.new(...), notArticles.new(...).

This will create several files:

invoke active_recordcreate db/migrate/<timestamp>_create_articles.rbcreate app/models/article.rbinvoke test_unitcreate test/models/article_test.rbcreate test/fixtures/articles.yml

The two files we'll focus on are the migration file(db/migrate/<timestamp>_create_articles.rb) and the model file(app/models/article.rb).

6.2 Database Migrations

Migrations are used to alter the structure of an application's database. InRails applications, migrations are written in Ruby so that they can bedatabase-agnostic.

Let's take a look at the contents of our new migration file:

class CreateArticles < ActiveRecord::Migration[7.1] def change create_table :articles do |t| t.string :title t.text :body t.timestamps end endend

The call to create_table specifies how the articles table should beconstructed. By default, the create_table method adds an id column as anauto-incrementing primary key. So the first record in the table will have anid of 1, the next record will have an id of 2, and so on.

Inside the block for create_table, two columns are defined: title andbody. These were added by the generator because we included them in ourgenerate command (bin/rails generate model Article title:string body:text).

On the last line of the block is a call to t.timestamps. This method definestwo additional columns named created_at and updated_at. As we will see,Rails will manage these for us, setting the values when we create or update amodel object.

Let's run our migration with the following command:

$ bin/rails db:migrate

The command will display output indicating that the table was created:

== CreateArticles: migrating ===================================-- create_table(:articles) -> 0.0018s== CreateArticles: migrated (0.0018s) ==========================

Now we can interact with the table using our model.

6.3 Using a Model to Interact with the Database

To play with our model a bit, we're going to use a feature of Rails called theconsole. The console is an interactive coding environment just like irb, butit also automatically loads Rails and our application code.

Let's launch the console with this command:

$ bin/rails console

You should see an irb prompt like:

Loading development environment (Rails 7.1.0)irb(main):001:0>

At this prompt, we can initialize a new Article object:

irb> article = Article.new(title: "Hello Rails", body: "I am on Rails!")

It's important to note that we have only initialized this object. This objectis not saved to the database at all. It's only available in the console at themoment. To save the object to the database, we must call save:

irb> article.save(0.1ms) begin transactionArticle Create (0.4ms) INSERT INTO "articles" ("title", "body", "created_at", "updated_at") VALUES (?, ?, ?, ?) [["title", "Hello Rails"], ["body", "I am on Rails!"], ["created_at", "2020-01-18 23:47:30.734416"], ["updated_at", "2020-01-18 23:47:30.734416"]](0.9ms) commit transaction=> true

The above output shows an INSERT INTO "articles" ... database query. Thisindicates that the article has been inserted into our table. And if we take alook at the article object again, we see something interesting has happened:

irb> article=> #<Article id: 1, title: "Hello Rails", body: "I am on Rails!", created_at: "2020-01-18 23:47:30", updated_at: "2020-01-18 23:47:30">

The id, created_at, and updated_at attributes of the object are now set.Rails did this for us when we saved the object.

When we want to fetch this article from the database, we can call findon the model and pass the id as an argument:

irb> Article.find(1)=> #<Article id: 1, title: "Hello Rails", body: "I am on Rails!", created_at: "2020-01-18 23:47:30", updated_at: "2020-01-18 23:47:30">

And when we want to fetch all articles from the database, we can call allon the model:

irb> Article.all=> #<ActiveRecord::Relation [#<Article id: 1, title: "Hello Rails", body: "I am on Rails!", created_at: "2020-01-18 23:47:30", updated_at: "2020-01-18 23:47:30">]>

This method returns an ActiveRecord::Relation object, whichyou can think of as a super-powered array.

Models are the final piece of the MVC puzzle. Next, we will connect all of thepieces together.

6.4 Showing a List of Articles

Let's go back to our controller in app/controllers/articles_controller.rb, andchange the index action to fetch all articles from the database:

class ArticlesController < ApplicationController def index @articles = Article.all endend

Controller instance variables can be accessed by the view. That means we canreference @articles in app/views/articles/index.html.erb. Let's open thatfile, and replace its contents with:

<h1>Articles</h1><ul> <% @articles.each do |article| %> <li> <%= article.title %> </li> <% end %></ul>

The above code is a mixture of HTML and ERB. ERB is a templating system thatevaluates Ruby code embedded in a document. Here, we can see two types of ERBtags: <% %> and <%= %>. The <% %> tag means "evaluate the enclosed Rubycode." The <%= %> tag means "evaluate the enclosed Ruby code, and output thevalue it returns." Anything you could write in a regular Ruby program can goinside these ERB tags, though it's usually best to keep the contents of ERB tagsshort, for readability.

Since we don't want to output the value returned by @articles.each, we'veenclosed that code in <% %>. But, since we do want to output the valuereturned by article.title (for each article), we've enclosed that code in<%= %>.

We can see the final result by visiting http://localhost:3000. (Remember thatbin/rails server must be running!) Here's what happens when we do that:

1. The browser makes a request: GET http://localhost:3000.
2. Our Rails application receives this request.
3. The Rails router maps the root route to the index action of ArticlesController.
4. The index action uses the Article model to fetch all articles in the database.
5. Rails automatically renders the app/views/articles/index.html.erb view.
6. The ERB code in the view is evaluated to output HTML.
7. The server sends a response containing the HTML back to the browser.

We've connected all the MVC pieces together, and we have our first controlleraction! Next, we'll move on to the second action.

7 CRUDit Where CRUDit Is Due

Almost all web applications involve CRUD (Create, Read, Update, and Delete) operations. Youmay even find that the majority of the work your application does is CRUD. Railsacknowledges this, and provides many features to help simplify code doing CRUD.

Let's begin exploring these features by adding more functionality to ourapplication.

7.1 Showing a Single Article

We currently have a view that lists all articles in our database. Let's add anew view that shows the title and body of a single article.

We start by adding a new route that maps to a new controller action (which wewill add next). Open config/routes.rb, and insert the last route shown here:

Rails.application.routes.draw do root "articles#index" get "/articles", to: "articles#index" get "/articles/:id", to: "articles#show"end

The new route is another get route, but it has something extra in its path::id. This designates a route parameter. A route parameter captures a segmentof the request's path, and puts that value into the params Hash, which isaccessible by the controller action. For example, when handling a request likeGET http://localhost:3000/articles/1, 1 would be captured as the value for:id, which would then be accessible as params[:id] in the show action ofArticlesController.

Let's add that show action now, below the index action inapp/controllers/articles_controller.rb:

class ArticlesController < ApplicationController def index @articles = Article.all end def show @article = Article.find(params[:id]) endend

The show action calls Article.find (mentionedpreviously) with the ID capturedby the route parameter. The returned article is stored in the @articleinstance variable, so it is accessible by the view. By default, the showaction will render app/views/articles/show.html.erb.

Let's create app/views/articles/show.html.erb, with the following contents:

<h1><%= @article.title %></h1><p><%= @article.body %></p>

Now we can see the article when we visit http://localhost:3000/articles/1!

To finish up, let's add a convenient way to get to an article's page. We'll linkeach article's title in app/views/articles/index.html.erb to its page:

<h1>Articles</h1><ul> <% @articles.each do |article| %> <li> <a href="/articles/<%= article.id %>"> <%= article.title %> </a> </li> <% end %></ul>

7.2 Resourceful Routing

So far, we've covered the "R" (Read) of CRUD. We will eventually cover the "C"(Create), "U" (Update), and "D" (Delete). As you might have guessed, we will doso by adding new routes, controller actions, and views. Whenever we have such acombination of routes, controller actions, and views that work together toperform CRUD operations on an entity, we call that entity a resource. Forexample, in our application, we would say an article is a resource.

Rails provides a routes method named resourcesthat maps all of the conventional routes for a collection of resources, such asarticles. So before we proceed to the "C", "U", and "D" sections, let's replacethe two get routes in config/routes.rb with resources:

Rails.application.routes.draw do root "articles#index" resources :articlesend

We can inspect what routes are mapped by running the bin/rails routes command:

$ bin/rails routes Prefix Verb URI Pattern Controller#Action root GET / articles#index articles GET /articles(.:format) articles#index new_article GET /articles/new(.:format) articles#new article GET /articles/:id(.:format) articles#show POST /articles(.:format) articles#createedit_article GET /articles/:id/edit(.:format) articles#edit PATCH /articles/:id(.:format) articles#update DELETE /articles/:id(.:format) articles#destroy

The resources method also sets up URL and path helper methods that we can useto keep our code from depending on a specific route configuration. The valuesin the "Prefix" column above plus a suffix of _url or _path form the namesof these helpers. For example, the article_path helper returns"/articles/#{article.id}" when given an article. We can use it to tidy up ourlinks in app/views/articles/index.html.erb:

<h1>Articles</h1><ul> <% @articles.each do |article| %> <li> <a href="<%= article_path(article) %>"> <%= article.title %> </a> </li> <% end %></ul>

However, we will take this one step further by using the link_tohelper. The link_to helper renders a link with its first argument as thelink's text and its second argument as the link's destination. If we pass amodel object as the second argument, link_to will call the appropriate pathhelper to convert the object to a path. For example, if we pass an article,link_to will call article_path. So app/views/articles/index.html.erbbecomes:

<h1>Articles</h1><ul> <% @articles.each do |article| %> <li> <%= link_to article.title, article %> </li> <% end %></ul>

Nice!

7.3 Creating a New Article

Now we move on to the "C" (Create) of CRUD. Typically, in web applications,creating a new resource is a multi-step process. First, the user requests a formto fill out. Then, the user submits the form. If there are no errors, then theresource is created and some kind of confirmation is displayed. Else, the formis redisplayed with error messages, and the process is repeated.

In a Rails application, these steps are conventionally handled by a controller'snew and create actions. Let's add a typical implementation of these actionsto app/controllers/articles_controller.rb, below the show action:

class ArticlesController < ApplicationController def index @articles = Article.all end def show @article = Article.find(params[:id]) end def new @article = Article.new end def create @article = Article.new(title: "...", body: "...") if @article.save redirect_to @article else render :new, status: :unprocessable_entity end endend

The new action instantiates a new article, but does not save it. This articlewill be used in the view when building the form. By default, the new actionwill render app/views/articles/new.html.erb, which we will create next.

The create action instantiates a new article with values for the title andbody, and attempts to save it. If the article is saved successfully, the actionredirects the browser to the article's page at "http://localhost:3000/articles/#{@article.id}".Else, the action redisplays the form by rendering app/views/articles/new.html.erbwith status code 422 Unprocessable Entity.The title and body here are dummy values. After we create the form, we will comeback and change these.

redirect_towill cause the browser to make a new request,whereas renderrenders the specified view for the current request.It is important to use redirect_to after mutating the database or application state.Otherwise, if the user refreshes the page, the browser will make the same request, and the mutation will be repeated.

7.3.1 Using a Form Builder

We will use a feature of Rails called a form builder to create our form. Usinga form builder, we can write a minimal amount of code to output a form that isfully configured and follows Rails conventions.

Let's create app/views/articles/new.html.erb with the following contents:

<h1>New Article</h1><%= form_with model: @article do |form| %> <div> <%= form.label :title %><br> <%= form.text_field :title %> </div> <div> <%= form.label :body %><br> <%= form.text_area :body %> </div> <div> <%= form.submit %> </div><% end %>

The form_withhelper method instantiates a form builder. In the form_with block we callmethods like labeland text_fieldon the form builder to output the appropriate form elements.

The resulting output from our form_with call will look like:

<form action="/articles" accept-charset="UTF-8" method="post"> <input type="hidden" name="authenticity_token" value="..."> <div> <label for="article_title">Title</label><br> <input type="text" name="article[title]" id="article_title"> </div> <div> <label for="article_body">Body</label><br> <textarea name="article[body]" id="article_body"></textarea> </div> <div> <input type="submit" name="commit" value="Create Article" data-disable-with="Create Article"> </div></form>

7.3.2 Using Strong Parameters

Submitted form data is put into the params Hash, alongside captured routeparameters. Thus, the create action can access the submitted title viaparams[:article][:title] and the submitted body via params[:article][:body].We could pass these values individually to Article.new, but that would beverbose and possibly error-prone. And it would become worse as we add morefields.

Instead, we will pass a single Hash that contains the values. However, we muststill specify what values are allowed in that Hash. Otherwise, a malicious usercould potentially submit extra form fields and overwrite private data. In fact,if we pass the unfiltered params[:article] Hash directly to Article.new,Rails will raise a ForbiddenAttributesError to alert us about the problem.So we will use a feature of Rails called Strong Parameters to filter params.Think of it as strong typingfor params.

Let's add a private method to the bottom of app/controllers/articles_controller.rbnamed article_params that filters params. And let's change create to useit:

class ArticlesController < ApplicationController def index @articles = Article.all end def show @article = Article.find(params[:id]) end def new @article = Article.new end def create @article = Article.new(article_params) if @article.save redirect_to @article else render :new, status: :unprocessable_entity end end private def article_params params.require(:article).permit(:title, :body) endend

7.3.3 Validations and Displaying Error Messages

As we have seen, creating a resource is a multi-step process. Handling invaliduser input is another step of that process. Rails provides a feature calledvalidations to help us deal with invalid user input. Validations are rulesthat are checked before a model object is saved. If any of the checks fail, thesave will be aborted, and appropriate error messages will be added to theerrors attribute of the model object.

Let's add some validations to our model in app/models/article.rb:

class Article < ApplicationRecord validates :title, presence: true validates :body, presence: true, length: { minimum: 10 }end

The first validation declares that a title value must be present. Becausetitle is a string, this means that the title value must contain at least onenon-whitespace character.

The second validation declares that a body value must also be present.Additionally, it declares that the body value must be at least 10 characterslong.

You may be wondering where the title and body attributes are defined.Active Record automatically defines model attributes for every table column, soyou don't have to declare those attributes in your model file.

With our validations in place, let's modify app/views/articles/new.html.erb todisplay any error messages for title and body:

<h1>New Article</h1><%= form_with model: @article do |form| %> <div> <%= form.label :title %><br> <%= form.text_field :title %> <% @article.errors.full_messages_for(:title).each do |message| %> <div><%= message %></div> <% end %> </div> <div> <%= form.label :body %><br> <%= form.text_area :body %><br> <% @article.errors.full_messages_for(:body).each do |message| %> <div><%= message %></div> <% end %> </div> <div> <%= form.submit %> </div><% end %>

The full_messages_formethod returns an array of user-friendly error messages for a specifiedattribute. If there are no errors for that attribute, the array will be empty.

To understand how all of this works together, let's take another look at thenew and create controller actions:

 def new @article = Article.new end def create @article = Article.new(article_params) if @article.save redirect_to @article else render :new, status: :unprocessable_entity end end

When we visit http://localhost:3000/articles/new, the GET /articles/newrequest is mapped to the new action. The new action does not attempt to save@article. Therefore, validations are not checked, and there will be no errormessages.

When we submit the form, the POST /articles request is mapped to the createaction. The create action does attempt to save @article. Therefore,validations are checked. If any validation fails, @article will not besaved, and app/views/articles/new.html.erb will be rendered with errormessages.

7.3.4 Finishing Up

We can now create an article by visiting http://localhost:3000/articles/new.To finish up, let's link to that page from the bottom ofapp/views/articles/index.html.erb:

<h1>Articles</h1><ul> <% @articles.each do |article| %> <li> <%= link_to article.title, article %> </li> <% end %></ul><%= link_to "New Article", new_article_path %>

7.4 Updating an Article

We've covered the "CR" of CRUD. Now let's move on to the "U" (Update). Updatinga resource is very similar to creating a resource. They are both multi-stepprocesses. First, the user requests a form to edit the data. Then, the usersubmits the form. If there are no errors, then the resource is updated. Else,the form is redisplayed with error messages, and the process is repeated.

These steps are conventionally handled by a controller's edit and updateactions. Let's add a typical implementation of these actions toapp/controllers/articles_controller.rb, below the create action:

class ArticlesController < ApplicationController def index @articles = Article.all end def show @article = Article.find(params[:id]) end def new @article = Article.new end def create @article = Article.new(article_params) if @article.save redirect_to @article else render :new, status: :unprocessable_entity end end def edit @article = Article.find(params[:id]) end def update @article = Article.find(params[:id]) if @article.update(article_params) redirect_to @article else render :edit, status: :unprocessable_entity end end private def article_params params.require(:article).permit(:title, :body) endend

Notice how the edit and update actions resemble the new and createactions.

The edit action fetches the article from the database, and stores it in@article so that it can be used when building the form. By default, the editaction will render app/views/articles/edit.html.erb.

The update action (re-)fetches the article from the database, and attemptsto update it with the submitted form data filtered by article_params. If novalidations fail and the update is successful, the action redirects the browserto the article's page. Else, the action redisplays the form — with errormessages — by rendering app/views/articles/edit.html.erb.

Our edit form will look the same as our new form. Even the code will be thesame, thanks to the Rails form builder and resourceful routing. The form builderautomatically configures the form to make the appropriate kind of request, basedon whether the model object has been previously saved.

Because the code will be the same, we're going to factor it out into a sharedview called a partial. Let's create app/views/articles/_form.html.erb withthe following contents:

<%= form_with model: article do |form| %> <div> <%= form.label :title %><br> <%= form.text_field :title %> <% article.errors.full_messages_for(:title).each do |message| %> <div><%= message %></div> <% end %> </div> <div> <%= form.label :body %><br> <%= form.text_area :body %><br> <% article.errors.full_messages_for(:body).each do |message| %> <div><%= message %></div> <% end %> </div> <div> <%= form.submit %> </div><% end %>

The above code is the same as our form in app/views/articles/new.html.erb,except that all occurrences of @article have been replaced with article.Because partials are shared code, it is best practice that they do not depend onspecific instance variables set by a controller action. Instead, we will passthe article to the partial as a local variable.

Let's update app/views/articles/new.html.erb to use the partial via render:

<h1>New Article</h1><%= render "form", article: @article %>

A partial's filename must be prefixed with an underscore, e.g._form.html.erb. But when rendering, it is referenced without theunderscore, e.g. render "form".

And now, let's create a very similar app/views/articles/edit.html.erb:

<h1>Edit Article</h1><%= render "form", article: @article %>

7.4.2 Finishing Up

We can now update an article by visiting its edit page, e.g.http://localhost:3000/articles/1/edit. To finish up, let's link to the editpage from the bottom of app/views/articles/show.html.erb:

<h1><%= @article.title %></h1><p><%= @article.body %></p><ul> <li><%= link_to "Edit", edit_article_path(@article) %></li></ul>

7.5 Deleting an Article

Finally, we arrive at the "D" (Delete) of CRUD. Deleting a resource is a simplerprocess than creating or updating. It only requires a route and a controlleraction. And our resourceful routing (resources :articles) already provides theroute, which maps DELETE /articles/:id requests to the destroy action ofArticlesController.

So, let's add a typical destroy action to app/controllers/articles_controller.rb,below the update action:

class ArticlesController < ApplicationController def index @articles = Article.all end def show @article = Article.find(params[:id]) end def new @article = Article.new end def create @article = Article.new(article_params) if @article.save redirect_to @article else render :new, status: :unprocessable_entity end end def edit @article = Article.find(params[:id]) end def update @article = Article.find(params[:id]) if @article.update(article_params) redirect_to @article else render :edit, status: :unprocessable_entity end end def destroy @article = Article.find(params[:id]) @article.destroy redirect_to root_path, status: :see_other end private def article_params params.require(:article).permit(:title, :body) endend

The destroy action fetches the article from the database, and calls destroyon it. Then, it redirects the browser to the root path with status code303 See Other.

We have chosen to redirect to the root path because that is our main accesspoint for articles. But, in other circ*mstances, you might choose to redirect toe.g. articles_path.

Now let's add a link at the bottom of app/views/articles/show.html.erb so thatwe can delete an article from its own page:

<h1><%= @article.title %></h1><p><%= @article.body %></p><ul> <li><%= link_to "Edit", edit_article_path(@article) %></li> <li><%= link_to "Destroy", article_path(@article), data: { turbo_method: :delete, turbo_confirm: "Are you sure?" } %></li></ul>

In the above code, we use the data option to set the data-turbo-method anddata-turbo-confirm HTML attributes of the "Destroy" link. Both of theseattributes hook into Turbo, which is included bydefault in fresh Rails applications. data-turbo-method="delete" will cause thelink to make a DELETE request instead of a GET request.data-turbo-confirm="Are you sure?" will cause a confirmation dialog to appearwhen the link is clicked. If the user cancels the dialog, the request will beaborted.

And that's it! We can now list, show, create, update, and delete articles!InCRUDable!

8 Adding a Second Model

It's time to add a second model to the application. The second model will handlecomments on articles.

8.1 Generating a Model

We're going to see the same generator that we used before when creatingthe Article model. This time we'll create a Comment model to hold areference to an article. Run this command in your terminal:

$ bin/rails generate model Comment commenter:string body:text article:references

This command will generate four files:

First, take a look at app/models/comment.rb:

class Comment < ApplicationRecord belongs_to :articleend

This is very similar to the Article model that you saw earlier. The differenceis the line belongs_to :article, which sets up an Active Record association.You'll learn a little about associations in the next section of this guide.

The (:references) keyword used in the shell command is a special data type for models.It creates a new column on your database table with the provided model name appended with an _idthat can hold integer values. To get a better understanding, analyze thedb/schema.rb file after running the migration.

In addition to the model, Rails has also made a migration to create thecorresponding database table:

class CreateComments < ActiveRecord::Migration[7.1] def change create_table :comments do |t| t.string :commenter t.text :body t.references :article, null: false, foreign_key: true t.timestamps end endend

The t.references line creates an integer column called article_id, an indexfor it, and a foreign key constraint that points to the id column of the articlestable. Go ahead and run the migration:

$ bin/rails db:migrate

Rails is smart enough to only execute the migrations that have not already beenrun against the current database, so in this case you will just see:

== CreateComments: migrating =================================================-- create_table(:comments) -> 0.0115s== CreateComments: migrated (0.0119s) ========================================

8.2 Associating Models

Active Record associations let you easily declare the relationship between twomodels. In the case of comments and articles, you could write out therelationships this way:

• Each comment belongs to one article.
• One article can have many comments.

In fact, this is very close to the syntax that Rails uses to declare thisassociation. You've already seen the line of code inside the Comment model(app/models/comment.rb) that makes each comment belong to an Article:

class Comment < ApplicationRecord belongs_to :articleend

You'll need to edit app/models/article.rb to add the other side of theassociation:

class Article < ApplicationRecord has_many :comments validates :title, presence: true validates :body, presence: true, length: { minimum: 10 }end

These two declarations enable a good bit of automatic behavior. For example, ifyou have an instance variable @article containing an article, you can retrieveall the comments belonging to that article as an array using@article.comments.

8.3 Adding a Route for Comments

As with the articles controller, we will need to add a route so that Railsknows where we would like to navigate to see comments. Open up theconfig/routes.rb file again, and edit it as follows:

Rails.application.routes.draw do root "articles#index" resources :articles do resources :comments endend

This creates comments as a nested resource within articles. This isanother part of capturing the hierarchical relationship that exists betweenarticles and comments.

For more information on routing, see the Rails Routingguide.

8.4 Generating a Controller

With the model in hand, you can turn your attention to creating a matchingcontroller. Again, we'll use the same generator we used before:

$ bin/rails generate controller Comments

This creates three files and one empty directory:

Like with any blog, our readers will create their comments directly afterreading the article, and once they have added their comment, will be sent backto the article show page to see their comment now listed. Due to this, ourCommentsController is there to provide a method to create comments and deletespam comments when they arrive.

So first, we'll wire up the Article show template(app/views/articles/show.html.erb) to let us make a new comment:

<h1><%= @article.title %></h1><p><%= @article.body %></p><ul> <li><%= link_to "Edit", edit_article_path(@article) %></li> <li><%= link_to "Destroy", article_path(@article), data: { turbo_method: :delete, turbo_confirm: "Are you sure?" } %></li></ul><h2>Add a comment:</h2><%= form_with model: [ @article, @article.comments.build ] do |form| %> <p> <%= form.label :commenter %><br> <%= form.text_field :commenter %> </p> <p> <%= form.label :body %><br> <%= form.text_area :body %> </p> <p> <%= form.submit %> </p><% end %>

This adds a form on the Article show page that creates a new comment bycalling the CommentsController create action. The form_with call here usesan array, which will build a nested route, such as /articles/1/comments.

Let's wire up the create in app/controllers/comments_controller.rb:

class CommentsController < ApplicationController def create @article = Article.find(params[:article_id]) @comment = @article.comments.create(comment_params) redirect_to article_path(@article) end private def comment_params params.require(:comment).permit(:commenter, :body) endend

You'll see a bit more complexity here than you did in the controller forarticles. That's a side-effect of the nesting that you've set up. Each requestfor a comment has to keep track of the article to which the comment is attached,thus the initial call to the find method of the Article model to get thearticle in question.

In addition, the code takes advantage of some of the methods available for anassociation. We use the create method on @article.comments to create andsave the comment. This will automatically link the comment so that it belongs tothat particular article.

Once we have made the new comment, we send the user back to the original articleusing the article_path(@article) helper. As we have already seen, this callsthe show action of the ArticlesController which in turn renders theshow.html.erb template. This is where we want the comment to show, so let'sadd that to the app/views/articles/show.html.erb.

<h1><%= @article.title %></h1><p><%= @article.body %></p><ul> <li><%= link_to "Edit", edit_article_path(@article) %></li> <li><%= link_to "Destroy", article_path(@article), data: { turbo_method: :delete, turbo_confirm: "Are you sure?" } %></li></ul><h2>Comments</h2><% @article.comments.each do |comment| %> <p> <strong>Commenter:</strong> <%= comment.commenter %> </p> <p> <strong>Comment:</strong> <%= comment.body %> </p><% end %><h2>Add a comment:</h2><%= form_with model: [ @article, @article.comments.build ] do |form| %> <p> <%= form.label :commenter %><br> <%= form.text_field :commenter %> </p> <p> <%= form.label :body %><br> <%= form.text_area :body %> </p> <p> <%= form.submit %> </p><% end %>

Now you can add articles and comments to your blog and have them show up in theright places.

9 Refactoring

Now that we have articles and comments working, take a look at theapp/views/articles/show.html.erb template. It is getting long and awkward. Wecan use partials to clean it up.

9.1 Rendering Partial Collections

First, we will make a comment partial to extract showing all the comments forthe article. Create the file app/views/comments/_comment.html.erb and put thefollowing into it:

<p> <strong>Commenter:</strong> <%= comment.commenter %></p><p> <strong>Comment:</strong> <%= comment.body %></p>

Then you can change app/views/articles/show.html.erb to look like thefollowing:

<h1><%= @article.title %></h1><p><%= @article.body %></p><ul> <li><%= link_to "Edit", edit_article_path(@article) %></li> <li><%= link_to "Destroy", article_path(@article), data: { turbo_method: :delete, turbo_confirm: "Are you sure?" } %></li></ul><h2>Comments</h2><%= render @article.comments %><h2>Add a comment:</h2><%= form_with model: [ @article, @article.comments.build ] do |form| %> <p> <%= form.label :commenter %><br> <%= form.text_field :commenter %> </p> <p> <%= form.label :body %><br> <%= form.text_area :body %> </p> <p> <%= form.submit %> </p><% end %>

This will now render the partial in app/views/comments/_comment.html.erb oncefor each comment that is in the @article.comments collection. As the rendermethod iterates over the @article.comments collection, it assigns eachcomment to a local variable named the same as the partial, in this casecomment, which is then available in the partial for us to show.

9.2 Rendering a Partial Form

Let us also move that new comment section out to its own partial. Again, youcreate a file app/views/comments/_form.html.erb containing:

<%= form_with model: [ @article, @article.comments.build ] do |form| %> <p> <%= form.label :commenter %><br> <%= form.text_field :commenter %> </p> <p> <%= form.label :body %><br> <%= form.text_area :body %> </p> <p> <%= form.submit %> </p><% end %>

Then you make the app/views/articles/show.html.erb look like the following:

<h1><%= @article.title %></h1><p><%= @article.body %></p><ul> <li><%= link_to "Edit", edit_article_path(@article) %></li> <li><%= link_to "Destroy", article_path(@article), data: { turbo_method: :delete, turbo_confirm: "Are you sure?" } %></li></ul><h2>Comments</h2><%= render @article.comments %><h2>Add a comment:</h2><%= render 'comments/form' %>

The second render just defines the partial template we want to render,comments/form. Rails is smart enough to spot the forward slash in thatstring and realize that you want to render the _form.html.erb file inthe app/views/comments directory.

The @article object is available to any partials rendered in the view becausewe defined it as an instance variable.

9.3 Using Concerns

Concerns are a way to make large controllers or models easier to understand and manage. This also has the advantage of reusability when multiple models (or controllers) share the same concerns. Concerns are implemented using modules that contain methods representing a well-defined slice of the functionality that a model or controller is responsible for. In other languages, modules are often known as mixins.

You can use concerns in your controller or model the same way you would use any module. When you first created your app with rails new blog, two folders were created within app/ along with the rest:

app/controllers/concernsapp/models/concerns

In the example below, we will implement a new feature for our blog that would benefit from using a concern. Then, we will create a concern, and refactor the code to use it, making the code more DRY and maintainable.

A blog article might have various statuses - for instance, it might be visible to everyone (i.e. public), or only visible to the author (i.e. private). It may also be hidden to all but still retrievable (i.e. archived). Comments may similarly be hidden or visible. This could be represented using a status column in each model.

First, let's run the following migrations to add status to Articles and Comments:

$ bin/rails generate migration AddStatusToArticles status:string$ bin/rails generate migration AddStatusToComments status:string

And next, let's update the database with the generated migrations:

$ bin/rails db:migrate

To choose the status for the existing articles and comments you can add a default value to the generated migration files by adding the default: "public" option and launch the migrations again. You can also call in a rails console Article.update_all(status: "public") and Comment.update_all(status: "public").

We also have to permit the :status key as part of the strong parameter, in app/controllers/articles_controller.rb:

 private def article_params params.require(:article).permit(:title, :body, :status) end

and in app/controllers/comments_controller.rb:

 private def comment_params params.require(:comment).permit(:commenter, :body, :status) end

Within the article model, after running a migration to add a status column using bin/rails db:migrate command, you would add:

class Article < ApplicationRecord has_many :comments validates :title, presence: true validates :body, presence: true, length: { minimum: 10 } VALID_STATUSES = ['public', 'private', 'archived'] validates :status, inclusion: { in: VALID_STATUSES } def archived? status == 'archived' endend

and in the Comment model:

class Comment < ApplicationRecord belongs_to :article VALID_STATUSES = ['public', 'private', 'archived'] validates :status, inclusion: { in: VALID_STATUSES } def archived? status == 'archived' endend

Then, in our index action template (app/views/articles/index.html.erb) we would use the archived? method to avoid displaying any article that is archived:

<h1>Articles</h1><ul> <% @articles.each do |article| %> <% unless article.archived? %> <li> <%= link_to article.title, article %> </li> <% end %> <% end %></ul><%= link_to "New Article", new_article_path %>

Similarly, in our comment partial view (app/views/comments/_comment.html.erb) we would use the archived? method to avoid displaying any comment that is archived:

<% unless comment.archived? %> <p> <strong>Commenter:</strong> <%= comment.commenter %> </p> <p> <strong>Comment:</strong> <%= comment.body %> </p><% end %>

However, if you look again at our models now, you can see that the logic is duplicated. If in the future we increase the functionality of our blog - to include private messages, for instance - we might find ourselves duplicating the logic yet again. This is where concerns come in handy.

A concern is only responsible for a focused subset of the model's responsibility; the methods in our concern will all be related to the visibility of a model. Let's call our new concern (module) Visible. We can create a new file inside app/models/concerns called visible.rb , and store all of the status methods that were duplicated in the models.

app/models/concerns/visible.rb

module Visible def archived? status == 'archived' endend

We can add our status validation to the concern, but this is slightly more complex as validations are methods called at the class level. The ActiveSupport::Concern (API Guide) gives us a simpler way to include them:

module Visible extend ActiveSupport::Concern VALID_STATUSES = ['public', 'private', 'archived'] included do validates :status, inclusion: { in: VALID_STATUSES } end def archived? status == 'archived' endend

Now, we can remove the duplicated logic from each model and instead include our new Visible module:

In app/models/article.rb:

class Article < ApplicationRecord include Visible has_many :comments validates :title, presence: true validates :body, presence: true, length: { minimum: 10 }end

and in app/models/comment.rb:

class Comment < ApplicationRecord include Visible belongs_to :articleend

Class methods can also be added to concerns. If we want to display a count of public articles or comments on our main page, we might add a class method to Visible as follows:

module Visible extend ActiveSupport::Concern VALID_STATUSES = ['public', 'private', 'archived'] included do validates :status, inclusion: { in: VALID_STATUSES } end class_methods do def public_count where(status: 'public').count end end def archived? status == 'archived' endend

Then in the view, you can call it like any class method:

<h1>Articles</h1>Our blog has <%= Article.public_count %> articles and counting!<ul> <% @articles.each do |article| %> <% unless article.archived? %> <li> <%= link_to article.title, article %> </li> <% end %> <% end %></ul><%= link_to "New Article", new_article_path %>

To finish up, we will add a select box to the forms, and let the user select the status when they create a new article or post a new comment. We can also select the status of the object, or a default of public if it hasn't been set yet. In app/views/articles/_form.html.erb, we can add:

<div> <%= form.label :status %><br> <%= form.select :status, Visible::VALID_STATUSES, selected: article.status || 'public' %></div>

and in app/views/comments/_form.html.erb:

<p> <%= form.label :status %><br> <%= form.select :status, Visible::VALID_STATUSES, selected: 'public' %></p>

Another important feature of a blog is being able to delete spam comments. To dothis, we need to implement a link of some sort in the view and a destroyaction in the CommentsController.

So first, let's add the delete link in theapp/views/comments/_comment.html.erb partial:

<% unless comment.archived? %> <p> <strong>Commenter:</strong> <%= comment.commenter %> </p> <p> <strong>Comment:</strong> <%= comment.body %> </p> <p> <%= link_to "Destroy Comment", [comment.article, comment], data: { turbo_method: :delete, turbo_confirm: "Are you sure?" } %> </p><% end %>

Clicking this new "Destroy Comment" link will fire off a DELETE/articles/:article_id/comments/:id to our CommentsController, which can thenuse this to find the comment we want to delete, so let's add a destroy actionto our controller (app/controllers/comments_controller.rb):

class CommentsController < ApplicationController def create @article = Article.find(params[:article_id]) @comment = @article.comments.create(comment_params) redirect_to article_path(@article) end def destroy @article = Article.find(params[:article_id]) @comment = @article.comments.find(params[:id]) @comment.destroy redirect_to article_path(@article), status: :see_other end private def comment_params params.require(:comment).permit(:commenter, :body, :status) endend

The destroy action will find the article we are looking at, locate the commentwithin the @article.comments collection, and then remove it from thedatabase and send us back to the show action for the article.

10.1 Deleting Associated Objects

If you delete an article, its associated comments will also need to bedeleted, otherwise they would simply occupy space in the database. Rails allowsyou to use the dependent option of an association to achieve this. Modify theArticle model, app/models/article.rb, as follows:

class Article < ApplicationRecord include Visible has_many :comments, dependent: :destroy validates :title, presence: true validates :body, presence: true, length: { minimum: 10 }end

11 Security

11.1 Basic Authentication

If you were to publish your blog online, anyone would be able to add, edit anddelete articles or delete comments.

Rails provides an HTTP authentication system that will work nicely inthis situation.

In the ArticlesController we need to have a way to block access to thevarious actions if the person is not authenticated. Here we can use the Railshttp_basic_authenticate_with method, which allows access to the requestedaction if that method allows it.

To use the authentication system, we specify it at the top of ourArticlesController in app/controllers/articles_controller.rb. In our case,we want the user to be authenticated on every action except index and show,so we write that:

class ArticlesController < ApplicationController http_basic_authenticate_with name: "dhh", password: "secret", except: [:index, :show] def index @articles = Article.all end # snippet for brevityend

We also want to allow only authenticated users to delete comments, so in theCommentsController (app/controllers/comments_controller.rb) we write:

class CommentsController < ApplicationController http_basic_authenticate_with name: "dhh", password: "secret", only: :destroy def create @article = Article.find(params[:article_id]) # ... end # snippet for brevityend

Now if you try to create a new article, you will be greeted with a basic HTTPAuthentication challenge:

After entering the correct username and password, you will remain authenticateduntil a different username and password is required or the browser is closed.

Other authentication methods are available for Rails applications. Two popularauthentication add-ons for Rails are theDevise rails engine andthe Authlogic gem,along with a number of others.

11.2 Other Security Considerations

Security, especially in web applications, is a broad and detailed area. Securityin your Rails application is covered in more depth inthe Ruby on Rails Security Guide.

12 What's Next?

Now that you've seen your first Rails application, you should feel free toupdate it and experiment on your own.

Remember, you don't have to do everything without help. As you need assistancegetting up and running with Rails, feel free to consult these supportresources:

• The Ruby on Rails Guides
• The Ruby on Rails mailing list

13 Configuration Gotchas

The easiest way to work with Rails is to store all external data as UTF-8. Ifyou don't, Ruby libraries and Rails will often be able to convert your nativedata into UTF-8, but this doesn't always work reliably, so you're better offensuring that all external data is UTF-8.

If you have made a mistake in this area, the most common symptom is a blackdiamond with a question mark inside appearing in the browser. Another commonsymptom is characters like "ü" appearing instead of "ü". Rails takes a numberof internal steps to mitigate common causes of these problems that can beautomatically detected and corrected. However, if you have external data that isnot stored as UTF-8, it can occasionally result in these kinds of issues thatcannot be automatically detected by Rails and corrected.

Two very common sources of data that are not UTF-8:

• Your text editor: Most text editors (such as TextMate), default to savingfiles as UTF-8. If your text editor does not, this can result in specialcharacters that you enter in your templates (such as é) to appear as a diamondwith a question mark inside in the browser. This also applies to your i18ntranslation files. Most editors that do not already default to UTF-8 (such assome versions of Dreamweaver) offer a way to change the default to UTF-8. Doso.
• Your database: Rails defaults to converting data from your database into UTF-8at the boundary. However, if your database is not using UTF-8 internally, itmay not be able to store all characters that your users enter. For instance,if your database is using Latin-1 internally, and your user enters a Russian,Hebrew, or Japanese character, the data will be lost forever once it entersthe database. If possible, use UTF-8 as the internal storage of your database.

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