bastos Action View
Comprehensive guide to Rails views, templates, partials, layouts, and view helpers.
Templates
ERB Syntax
<%# Comment - not rendered %>
<% code %> <%# Execute Ruby, no output %>
<%= expression %> <%# Output result (escaped) %>
<%== raw_html %> <%# Output without escaping (use carefully) %>
<%- code -%> <%# Suppress leading/trailing whitespace %>
Common ERB Patterns
<%# Conditionals %>
<% if @user.admin? %>
<span class="badge">Admin</span>
<% end %>
<%# Iteration %>
<% @articles.each do |article| %>
<article>
<h2><%= article.title %></h2>
<p><%= truncate(article.body, length: 100) %></p>
</article>
<% end %>
<%# Safe output %>
<%= sanitize(@article.body) %>
<%= raw(@trusted_html) %>
Partials
Partials are reusable view fragments. Filename starts with underscore.
Basic Partial
<%# app/views/articles/_article.html.erb %>
<article id="<%= dom_id(article) %>">
<h2><%= article.title %></h2>
<p><%= article.body %></p>
</article>
<%# Render partial %>
<%= render "article", article: @article %>
<%= render partial: "article", locals: { article: @article } %>
Collection Rendering
<%# Renders _article.html.erb for each item %>
<%= render @articles %>
<%# Explicit collection %>
<%= render partial: "article", collection: @articles %>
<%# With spacer %>
<%= render partial: "article", collection: @articles, spacer_template: "article_divider" %>
<%# Cached collection %>
<%= render partial: "article", collection: @articles, cached: true %>
Local Variables
<%# Counter and iteration info available %>
<%# article_counter (0-indexed) %>
<%# article_iteration.first?, .last?, .index, .size %>
<%# Strict locals (Rails 7.1+) %>
<%# locals: (article:, show_author: true) -%>
<article>
<h2><%= article.title %></h2>
<% if show_author %>
<p>By <%= article.author.name %></p>
<% end %>
</article>
Partial Layouts
<%# Wrap partial in a layout %>
<%= render partial: "article", layout: "card", locals: { article: @article } %>
<%# app/views/shared/_card.html.erb %>
<div class="card">
<%= yield %>
</div>
Layouts
Application Layout
<%# app/views/layouts/application.html.erb %>
<!DOCTYPE html>
<html>
<head>
<title><%= content_for(:title) || "My App" %></title>
<%= csrf_meta_tags %>
<%= csp_meta_tag %>
<%= stylesheet_link_tag "application", "data-turbo-track": "reload" %>
<%= javascript_importmap_tags %>
<%= yield :head %>
</head>
<body>
<%= render "shared/header" %>
<% if notice %>
<div class="notice"><%= notice %></div>
<% end %>
<% if alert %>
<div class="alert"><%= alert %></div>
<% end %>
<main>
<%= yield %>
</main>
<%= render "shared/footer" %>
</body>
</html>
Content For
<%# In view %>
<% content_for :title, "My Page Title" %>
<% content_for :head do %>
<%= stylesheet_link_tag "custom" %>
<% end %>
<% content_for :sidebar do %>
<nav>Sidebar content</nav>
<% end %>
<%# In layout %>
<%= content_for?(:sidebar) ? yield(:sidebar) : render("default_sidebar") %>
Controller-Specific Layouts
class AdminController < ApplicationController
layout "admin"
end
class ArticlesController < ApplicationController
layout "article", only: [:show]
layout :determine_layout
private
def determine_layout
current_user&.admin? ? "admin" : "application"
end
end
Form Helpers
form_with
<%# Model-backed form %>
<%= form_with model: @article do |form| %>
<%= form.label :title %>
<%= form.text_field :title %>
<%= form.label :body %>
<%= form.text_area :body, rows: 10 %>
<%= form.label :status %>
<%= form.select :status, Article::STATUSES %>
<%= form.submit %>
<% end %>
<%# URL-based form %>
<%= form_with url: search_path, method: :get do |form| %>
<%= form.text_field :q, placeholder: "Search..." %>
<%= form.submit "Search" %>
<% end %>
Form Fields
<%# Text inputs %>
<%= form.text_field :name %>
<%= form.email_field :email %>
<%= form.password_field :password %>
<%= form.telephone_field :phone %>
<%= form.url_field :website %>
<%= form.number_field :quantity, min: 1, max: 100 %>
<%= form.range_field :rating, min: 1, max: 5 %>
<%= form.search_field :q %>
<%= form.text_area :description, rows: 5 %>
<%# Hidden %>
<%= form.hidden_field :status, value: "draft" %>
<%# Checkboxes and radios %>
<%= form.check_box :published %>
<%= form.radio_button :status, "draft" %>
<%= form.radio_button :status, "published" %>
<%# Select %>
<%= form.select :category_id, Category.pluck(:name, :id) %>
<%= form.select :role, %w[admin editor viewer], { include_blank: "Select role" } %>
<%# Collection select %>
<%= form.collection_select :category_id, Category.all, :id, :name %>
<%= form.collection_radio_buttons :status, Status.all, :id, :name %>
<%= form.collection_check_boxes :tag_ids, Tag.all, :id, :name %>
<%# Date/time %>
<%= form.date_field :published_on %>
<%= form.time_field :start_time %>
<%= form.datetime_local_field :event_at %>
<%= form.date_select :birthday %>
<%= form.time_zone_select :time_zone %>
<%# File upload %>
<%= form.file_field :avatar %>
<%= form.file_field :images, multiple: true %>
Nested Forms
# Model
class Article < ApplicationRecord
has_many :comments
accepts_nested_attributes_for :comments, allow_destroy: true
end
<%= form_with model: @article do |form| %>
<%= form.text_field :title %>
<%= form.fields_for :comments do |comment_form| %>
<%= comment_form.text_area :body %>
<%= comment_form.check_box :_destroy %>
<%= comment_form.label :_destroy, "Delete" %>
<% end %>
<%= form.submit %>
<% end %>
URL Helpers
<%# Links %>
<%= link_to "Home", root_path %>
<%= link_to "Article", @article %>
<%= link_to "Edit", edit_article_path(@article) %>
<%= link_to "Delete", @article, method: :delete, data: { turbo_method: :delete, turbo_confirm: "Sure?" } %>
<%# With block %>
<%= link_to article_path(@article) do %>
<strong><%= @article.title %></strong>
<% end %>
<%# Button (creates form) %>
<%= button_to "Subscribe", subscriptions_path, method: :post %>
<%# Email %>
<%= mail_to "support@example.com" %>
<%= mail_to "support@example.com", "Contact Us", subject: "Help Request" %>
<%# Current page check %>
<%= link_to "Home", root_path, class: ("active" if current_page?(root_path)) %>
Tag Helpers
<%# Modern tag helper syntax %>
<%= tag.div class: "container" do %>
<%= tag.h1 @article.title %>
<%= tag.p @article.body, class: "content" %>
<% end %>
<%# With data attributes %>
<%= tag.div data: { controller: "toggle", action: "click->toggle#switch" } do %>
Content
<% end %>
<%# Self-closing tags %>
<%= tag.br %>
<%= tag.hr %>
<%= tag.input type: "text", name: "query" %>
<%# class_names / token_list %>
<%= tag.div class: class_names("base", active: @active, hidden: @hidden) %>
Asset Helpers
<%# Images %>
<%= image_tag "logo.png" %>
<%= image_tag "logo.png", alt: "Logo", class: "logo", size: "100x50" %>
<%= image_tag @user.avatar, fallback: "default_avatar.png" %>
<%# Stylesheets %>
<%= stylesheet_link_tag "application", media: "all" %>
<%= stylesheet_link_tag "print", media: "print" %>
<%# JavaScript %>
<%= javascript_include_tag "application" %>
<%= javascript_importmap_tags %>
<%# Favicon %>
<%= favicon_link_tag "favicon.ico" %>
<%# Video/Audio %>
<%= video_tag "intro.mp4", controls: true, autoplay: false %>
<%= audio_tag "podcast.mp3", controls: true %>
Text Helpers
<%# Truncate %>
<%= truncate(@article.body, length: 100) %>
<%= truncate(@article.body, length: 100, omission: "... (more)") %>
<%# Excerpt %>
<%= excerpt(@article.body, "Rails", radius: 25) %>
<%# Pluralize %>
<%= pluralize(@comments.count, "comment") %>
<%# Word wrap %>
<%= word_wrap(@text, line_width: 80) %>
<%# Simple format (converts newlines to <br> and paragraphs) %>
<%= simple_format(@article.body) %>
<%# Highlight %>
<%= highlight(@article.body, "Rails") %>
Number Helpers
<%= number_to_currency(1234.56) %> <%# $1,234.56 %>
<%= number_to_currency(1234.56, unit: "€") %> <%# €1,234.56 %>
<%= number_to_percentage(75.5) %> <%# 75.500% %>
<%= number_to_percentage(75.5, precision: 0) %> <%# 76% %>
<%= number_with_delimiter(12345678) %> <%# 12,345,678 %>
<%= number_with_precision(111.2345, precision: 2) %> <%# 111.23 %>
<%= number_to_human(1234567) %> <%# 1.23 Million %>
<%= number_to_human_size(1234567) %> <%# 1.18 MB %>
<%= number_to_phone(5551234567) %> <%# 555-123-4567 %>
Date Helpers
<%= distance_of_time_in_words(Time.current, 3.days.from_now) %> <%# about 3 days %>
<%= time_ago_in_words(@article.created_at) %> <%# 2 hours ago %>
Sanitization
<%# Remove dangerous HTML %>
<%= sanitize(@user_input) %>
<%# Allow specific tags %>
<%= sanitize(@content, tags: %w[p br strong em]) %>
<%# Strip all tags %>
<%= strip_tags(@html_content) %>
<%# Strip links but keep text %>
<%= strip_links(@content_with_links) %>
Additional Resources
Reference Files
references/form-patterns.md- Complex form patterns, custom form buildersreferences/view-helpers.md- Creating custom helpers, helper organization