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<h2>Action View 綜覽</h2><p>讀完本篇，您將了解：</p>
<ul>
<li>什麼是 Action View、如何在 Rails 裡使用。</li>
<li>如何善用模版，局部頁面與版型。</li>
<li>Action View 提供的輔助方法、如何自己寫輔助方法。</li>
<li>如何使用本地化的 View。</li>
<li>如何在 Rails 之外使用 Action View。</li>
</ul>
<div id="subCol">
<h3 class="chapter"><img src="images/chapters_icon.gif" alt="" />Chapters</h3>
<ol class="chapters">
<li><a href="#%E4%BB%80%E9%BA%BC%E6%98%AF-action-view%EF%BC%9F">什麼是 Action View？</a></li>
<li><a href="#%E5%9C%A8-rails-%E4%B8%AD%E4%BD%BF%E7%94%A8-action-view">在 Rails 中使用 Action View</a></li>
<li>
<a href="#%E6%A8%A1%E7%89%88%E3%80%81%E5%B1%80%E9%83%A8%E9%A0%81%E9%9D%A2%E5%8F%8A%E7%89%88%E5%9E%8B">模版、局部頁面及版型</a>
<ul>
<li><a href="#%E6%A8%A1%E7%89%88">模版</a></li>
<li><a href="#%E5%B1%80%E9%83%A8%E9%A0%81%E9%9D%A2">局部頁面</a></li>
<li><a href="#layouts">Layouts</a></li>
</ul>
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<li><a href="#partial-layouts">Partial Layouts</a></li>
<li><a href="#view-paths">View Paths</a></li>
<li>
<a href="#overview-of-helpers-provided-by-action-view">Overview of helpers provided by Action View</a>
<ul>
<li><a href="#recordtaghelper">RecordTagHelper</a></li>
<li><a href="#assettaghelper">AssetTagHelper</a></li>
<li><a href="#atomfeedhelper">AtomFeedHelper</a></li>
<li><a href="#benchmarkhelper">BenchmarkHelper</a></li>
<li><a href="#cachehelper">CacheHelper</a></li>
<li><a href="#capturehelper">CaptureHelper</a></li>
<li><a href="#datehelper">DateHelper</a></li>
<li><a href="#debughelper">DebugHelper</a></li>
<li><a href="#formhelper">FormHelper</a></li>
<li><a href="#formoptionshelper">FormOptionsHelper</a></li>
<li><a href="#formtaghelper">FormTagHelper</a></li>
<li><a href="#javascripthelper">JavaScriptHelper</a></li>
<li><a href="#numberhelper">NumberHelper</a></li>
<li><a href="#sanitizehelper">SanitizeHelper</a></li>
<li><a href="#csrfhelper">CsrfHelper</a></li>
</ul>
</li>
<li><a href="#localized-views">Localized Views</a></li>
</ol>
</div>
</div>
</div>
<div id="container">
<div class="wrapper">
<div id="mainCol">
<h3 id="什麼是-action-view？">1 什麼是 Action View？</h3><p>Action View 與 Action Controller 是 Action Pack 中的兩個主要元件。 在 Rails 裡，網路請求是由 Action Pack 負責處理的。此過程分成處理邏輯的 controller 步驟，及算繪模版的 view 步驟。通常 Action Controller 是與資料庫溝通，根據需求來執行 CRUD 操作。而 Action View 則接著負責編譯出回應。</p><p>Action View 模版是由嵌入 HTML 的 Ruby 撰寫而成。為了避免模版充斥混亂的程式碼，Action View 提供了許多輔助方法，用來撰寫表單、日期及字串等。當應用程式成長時，加入自訂的輔助方法也很容易。</p><div class="note"><p>部份 Action View 的功能與 Active Record 綁在一起。但這不代表 Action View 依賴於 Action Record。Active View 是個獨立的函式庫，可以和其它的 Ruby 函式庫一起使用。</p></div><h3 id="在-rails-中使用-action-view">2 在 Rails 中使用 Action View</h3><p>每個 Controller 在 <code>app/views</code> 中都會有一個對應的資料夾，裡面包含了該 Controller 的模板檔案。這些檔案用來顯示 Controller 各個動作的結果頁面。</p><p>看看 Rails 用 <code>scaffold</code> 命令建立新資源時，預設會產生哪些檔案：</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
$ bin/rails generate scaffold article
[...]
invoke scaffold_controller
create app/controllers/articles_controller.rb
invoke erb
create app/views/articles
create app/views/articles/index.html.erb
create app/views/articles/edit.html.erb
create app/views/articles/show.html.erb
create app/views/articles/new.html.erb
create app/views/articles/_form.html.erb
[...]
</pre>
</div>
<p>Rails 的 View 有命名慣例。通常 View 的檔名和 Controller 的動作同名，如上所示。例如 <code>articles_controller.rb</code> 的 <code>index</code> 動作使用 <code>app/views/articles</code> 資料夾中的 <code>index.html.erb</code> 這個 View 檔案。回傳給用戶端的完整 HTML 是由這個 ERB 檔案、版型，以及其它引用的局部頁面組成。本篇之後會對這三種 View 做更詳細的介紹。</p><h3 id="模版、局部頁面及版型">3 模版、局部頁面及版型</h3><p>上面有提到過，最終輸出的 HTML 由三種 Rails 元素組成：模版、局部頁面以及版型。底下簡單介紹這三種元素。</p><h4 id="模版">3.1 模版</h4><p>Action View 的模版有數種不同的寫法。如果模版的副檔名是 <code>erb</code> 的話，那麼這個模版是混合 ERB （Ruby 內建）和 HTML。若模版的副檔名是 <code>.builder</code>，則是使用了 <code>Builder::XmlMarkup</code> 函式庫。</p><p>Rails 支援多種模版系統，使用副檔名來做區隔。例如使用 ERB 模版系統的 HTML 檔案，副檔名是 <code>.html.erb</code>。</p><h5 id="erb">3.1.1 ERB</h5><p>在 ERB 模版裡，Ruby 程式碼會放在 <code><% %></code> 或是 <code><%= %></code> 標籤裡。<code><% %></code> 標籤是用來執行不會回傳任何值的 Ruby 程式碼，例如條件判斷、迴圈或是區塊等等，而 <code><%= %></code> 標籤則是用來輸出結果。</p><p>考慮以下 <code>names</code> 迴圈：</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
<h1>Names of all the people</h1>
<% @people.each do |person| %>
Name: <%= person.name %><br>
<% end %>
</pre>
</div>
<p>迴圈放在普通嵌入標籤（<code><% %></code>）裡，而需要顯示的 <code>name</code> 則是放在會輸出結果的標籤（<code><%= %></code>）中。注意這不是建議的使用方法，Ruby 一般的輸出函式如 <code>print</code> 或是 <code>puts</code> 是無法將結果顯示在 ERB 模版裡。所以以下的範例是不正確的：</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
<%# WRONG %>
Hi, Mr. <% puts "Frodo" %>
</pre>
</div>
<p>要去掉開頭或結尾的空白，可以用 <code><%-</code> <code>-%></code> 來取代 <code><%</code> 及 <code>%></code>。</p><h5 id="builder">3.1.2 Builder</h5><p>Builder 模版 ERB 的替代方案，比 ERB 需要更多程式設計。在產生 XML 時特別有用。在副檔名為 <code>.builder</code> 的模版裡，可以直接使用名為 <code>xml</code> 的 <code>XmlMarkup</code> 物件。</p><p>以下是一些簡單的範例：</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
xml.em("emphasized")
xml.em { xml.b("emph & bold") }
xml.a("A Link", "href" => "http://rubyonrails.org")
xml.target("name" => "compile", "option" => "fast")
</pre>
</div>
<p>會產生：</p><div class="code_container">
<pre class="brush: xml; gutter: false; toolbar: false">
<em>emphasized</em>
<em><b>emph &amp; bold</b></em>
<a href="http://rubyonrails.org">A link</a>
<target option="fast" name="compile" />
</pre>
</div>
<p>傳入區塊的方法會被當成一個巢狀 XML 標籤的外層，區塊內容則會嵌套成內層的標籤來處理。見下例：</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
xml.div {
xml.h1(@person.name)
xml.p(@person.bio)
}
</pre>
</div>
<p>會生成：</p><div class="code_container">
<pre class="brush: xml; gutter: false; toolbar: false">
<div>
<h1>David Heinemeier Hansson</h1>
<p>A product of Danish Design during the Winter of '79...</p>
</div>
</pre>
</div>
<p>以下是一個 Basecamp 中實際用到的完整 RSS 範例：</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
xml.rss("version" => "2.0", "xmlns:dc" => "http://purl.org/dc/elements/1.1/") do
xml.channel do
xml.title(@feed_title)
xml.link(@url)
xml.description "Basecamp: Recent items"
xml.language "en-us"
xml.ttl "40"
for item in @recent_items
xml.item do
xml.title(item_title(item))
xml.description(item_description(item)) if item_description(item)
xml.pubDate(item_pubDate(item))
xml.guid(@person.firm.account.url + @recent_items.url(item))
xml.link(@person.firm.account.url + @recent_items.url(item))
xml.tag!("dc:creator", item.author_name) if item_has_creator?(item)
end
end
end
end
</pre>
</div>
<h5 id="模版快取">3.1.3 模版快取</h5><p>Rail 預設會編譯所有的模版來進行算繪。當你修改某個模板後，development 模式下的 Rails 會重新檢查及編譯它。</p><h4 id="局部頁面">3.2 局部頁面</h4><p>局部頁面模板 - 簡稱局部頁面 - 用來把算繪過程拆成更好管理的小片段的工具。有了局部頁面，可以把某些特定內容的算繪移到單獨的檔案。</p><h5 id="局部頁面命名">3.2.1 局部頁面命名</h5><p>在 view 檔案中，你要用 <code>render</code> 來算繪局部頁面</p><div class="code_container">
<pre class="brush: ruby; html-script: true; gutter: false; toolbar: false">
<%= render "menu" %>
</pre>
</div>
<p>這樣會在呼叫的地方，找到目前資料夾下的 <code>_meun.html.erb</code> 檔案來算繪。注意名字開頭的"底線" (_): 局部頁面的命名規則是由底線開頭。用來與一般的 view 區別。但在引用局部頁面時，呼叫的語法不用加上底線。如果要呼叫其它資料夾下的局部頁面也是一樣不加底線：</p><div class="code_container">
<pre class="brush: ruby; html-script: true; gutter: false; toolbar: false">
<%= render "shared/menu" %>
</pre>
</div>
<p>這樣會去找到 <code>app/views/shared/_menu.html.erb</code> 檔案來引入。</p><h5 id="使用局部頁面來簡化-views">3.2.2 使用局部頁面來簡化 Views</h5><p>局部頁面的一個用途是把它拿來當副程式；把細節的部份拆出去，讓你更容易理解 view 的全局。舉例來說，你可能看過長這樣的 view：</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
<%= render "shared/ad_banner" %>
<h1>Products</h1>
<p>Here are a few of our fine products:</p>
<% @products.each do |product| %>
<%= render partial: "product", locals: {product: product} %>
<% end %>
<%= render "shared/footer" %>
</pre>
</div>
<p>這裡的 <code>_ad_banner.html.erb</code> 及 <code>_footer.html.erb</code> 局部頁面可以包含你的應用程式裡其它頁面可以共用的內容。這樣一來在寫各個頁面時，就不需要去關注這些瑣碎的細節。</p><h5 id="as-及-object-選項">3.2.3 <code>as</code> 及 <code>object</code> 選項</h5><p><code>ActionView::Partials::PartialRenderer</code> 預設會有個物件，存在與模版名稱相同的變數中。例如：</p><div class="code_container">
<pre class="brush: ruby; html-script: true; gutter: false; toolbar: false">
<%= render partial: "product" %>
</pre>
</div>
<p>在局部頁面中，我們會把 <code>@product</code> 存在區域變數 <code>product</code> 中。就如同我們寫了：</p><div class="code_container">
<pre class="brush: ruby; html-script: true; gutter: false; toolbar: false">
<%= render partial: "product", locals: {product: @product} %>
</pre>
</div>
<p>用 <code>as</code> 選項，我們可以改用其它的區域變數名稱。例如當我們想用 <code>item</code> 取代 <code>product</code> 時，我們會這樣寫：</p><div class="code_container">
<pre class="brush: ruby; html-script: true; gutter: false; toolbar: false">
<%= render partial: "product", as: "item" %>
</pre>
</div>
<p>而 <code>object</code> 選項讓我們可以直接指定要算繪到局部頁面中的物件。這會用於模版頁面的物件存在其它地方時。(例如： 要算繪的物件是另一個實例物件，或是存在某個區域變數裡。)</p><p>例如想用這種方法寫時：</p><div class="code_container">
<pre class="brush: ruby; html-script: true; gutter: false; toolbar: false">
<%= render partial: "product", locals: {product: @item} %>
</pre>
</div>
<p>我們會改成這樣：</p><div class="code_container">
<pre class="brush: ruby; html-script: true; gutter: false; toolbar: false">
<%= render partial: "product", object: @item %>
</pre>
</div>
<p><code>object</code> 及 <code>as</code> 選項可以同時用：</p><div class="code_container">
<pre class="brush: ruby; html-script: true; gutter: false; toolbar: false">
<%= render partial: "product", object: @item, as: "item" %>
</pre>
</div>
<h5 id="rendering-collections">3.2.4 Rendering Collections</h5><p>It is very common that a template needs to iterate over a collection and render a sub-template for each of the elements. This pattern has been implemented as a single method that accepts an array and renders a partial for each one of the elements in the array.</p><p>So this example for rendering all the products:</p><div class="code_container">
<pre class="brush: ruby; html-script: true; gutter: false; toolbar: false">
<% @products.each do |product| %>
<%= render partial: "product", locals: { product: product } %>
<% end %>
</pre>
</div>
<p>can be rewritten in a single line:</p><div class="code_container">
<pre class="brush: ruby; html-script: true; gutter: false; toolbar: false">
<%= render partial: "product", collection: @products %>
</pre>
</div>
<p>When a partial is called like this (eg. with a collection), the individual instances of the partial have access to the member of the collection being rendered via a variable named after the partial. In this case, the partial is <code>_product</code>, and within it you can refer to <code>product</code> to get the instance that is being rendered.</p><p>You can use a shorthand syntax for rendering collections. Assuming <code>@products</code> is a collection of <code>Product</code> instances, you can simply write the following to produce the same result:</p><div class="code_container">
<pre class="brush: ruby; html-script: true; gutter: false; toolbar: false">
<%= render @products %>
</pre>
</div>
<p>Rails determines the name of the partial to use by looking at the model name in the collection, <code>Product</code> in this case. In fact, you can even create a heterogeneous collection and render it this way, and Rails will choose the proper partial for each member of the collection.</p><h5 id="spacer-templates">3.2.5 Spacer Templates</h5><p>You can also specify a second partial to be rendered between instances of the main partial by using the <code>:spacer_template</code> option:</p><div class="code_container">
<pre class="brush: ruby; html-script: true; gutter: false; toolbar: false">
<%= render partial: @products, spacer_template: "product_ruler" %>
</pre>
</div>
<p>Rails will render the <code>_product_ruler</code> partial (with no data passed to it) between each pair of <code>_product</code> partials.</p><h4 id="layouts">3.3 Layouts</h4><p>Layouts can be used to render a common view template around the results of Rails controller actions. Typically, every Rails application has a couple of overall layouts that most pages are rendered within. For example, a site might have a layout for a logged in user, and a layout for the marketing or sales side of the site. The logged in user layout might include top-level navigation that should be present across many controller actions. The sales layout for a SaaS app might include top-level navigation for things like "Pricing" and "Contact Us." You would expect each layout to have a different look and feel. You can read more details about Layouts in the <a href="layouts_and_rendering.html">Layouts and Rendering in Rails</a> guide.</p><h3 id="partial-layouts">4 Partial Layouts</h3><p>Partials can have their own layouts applied to them. These layouts are different than the ones that are specified globally for the entire action, but they work in a similar fashion.</p><p>Let's say we're displaying an article on a page, that should be wrapped in a <code>div</code> for display purposes. First, we'll create a new <code>Article</code>:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
Article.create(body: 'Partial Layouts are cool!')
</pre>
</div>
<p>In the <code>show</code> template, we'll render the <code>_article</code> partial wrapped in the <code>box</code> layout:</p><p><strong>articles/show.html.erb</strong></p><div class="code_container">
<pre class="brush: ruby; html-script: true; gutter: false; toolbar: false">
<%= render partial: 'article', layout: 'box', locals: {article: @article} %>
</pre>
</div>
<p>The <code>box</code> layout simply wraps the <code>_article</code> partial in a <code>div</code>:</p><p><strong>articles/_box.html.erb</strong></p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
<div class='box'>
<%= yield %>
</div>
</pre>
</div>
<p>The <code>_article</code> partial wraps the article's <code>body</code> in a <code>div</code> with the <code>id</code> of the article using the <code>div_for</code> helper:</p><p><strong>articles/_article.html.erb</strong></p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
<%= div_for(article) do %>
<p><%= article.body %></p>
<% end %>
</pre>
</div>
<p>this would output the following:</p><div class="code_container">
<pre class="brush: xml; gutter: false; toolbar: false">
<div class='box'>
<div id='article_1'>
<p>Partial Layouts are cool!</p>
</div>
</div>
</pre>
</div>
<p>Note that the partial layout has access to the local <code>article</code> variable that was passed into the <code>render</code> call. However, unlike application-wide layouts, partial layouts still have the underscore prefix.</p><p>You can also render a block of code within a partial layout instead of calling <code>yield</code>. For example, if we didn't have the <code>_article</code> partial, we could do this instead:</p><p><strong>articles/show.html.erb</strong></p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
<% render(layout: 'box', locals: {article: @article}) do %>
<%= div_for(article) do %>
<p><%= article.body %></p>
<% end %>
<% end %>
</pre>
</div>
<p>Supposing we use the same <code>_box</code> partial from above, this would produce the same output as the previous example.</p><h3 id="view-paths">5 View Paths</h3><div class="todo"><p>..</p></div><h3 id="overview-of-helpers-provided-by-action-view">6 Overview of helpers provided by Action View</h3><p>WIP: Not all the helpers are listed here. For a full list see the <a href="http://api.rubyonrails.org/classes/ActionView/Helpers.html">API documentation</a></p><p>The following is only a brief overview summary of the helpers available in Action View. It's recommended that you review the <a href="http://api.rubyonrails.org/classes/ActionView/Helpers.html">API Documentation</a>, which covers all of the helpers in more detail, but this should serve as a good starting point.</p><h4 id="recordtaghelper">6.1 RecordTagHelper</h4><p>This module provides methods for generating container tags, such as <code>div</code>, for your record. This is the recommended way of creating a container for render your Active Record object, as it adds an appropriate class and id attributes to that container. You can then refer to those containers easily by following the convention, instead of having to think about which class or id attribute you should use.</p><h5 id="content-tag-for">6.1.1 content_tag_for</h5><p>Renders a container tag that relates to your Active Record Object.</p><p>For example, given <code>@article</code> is the object of <code>Article</code> class, you can do:</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
<%= content_tag_for(:tr, @article) do %>
<td><%= @article.title %></td>
<% end %>
</pre>
</div>
<p>This will generate this HTML output:</p><div class="code_container">
<pre class="brush: xml; gutter: false; toolbar: false">
<tr id="article_1234" class="article">
<td>Hello World!</td>
</tr>
</pre>
</div>
<p>You can also supply HTML attributes as an additional option hash. For example:</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
<%= content_tag_for(:tr, @article, class: "frontpage") do %>
<td><%= @article.title %></td>
<% end %>
</pre>
</div>
<p>Will generate this HTML output:</p><div class="code_container">
<pre class="brush: xml; gutter: false; toolbar: false">
<tr id="article_1234" class="article frontpage">
<td>Hello World!</td>
</tr>
</pre>
</div>
<p>You can pass a collection of Active Record objects. This method will loop through your objects and create a container for each of them. For example, given <code>@articles</code> is an array of two <code>Article</code> objects:</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
<%= content_tag_for(:tr, @articles) do |article| %>
<td><%= article.title %></td>
<% end %>
</pre>
</div>
<p>Will generate this HTML output:</p><div class="code_container">
<pre class="brush: xml; gutter: false; toolbar: false">
<tr id="article_1234" class="article">
<td>Hello World!</td>
</tr>
<tr id="article_1235" class="article">
<td>Ruby on Rails Rocks!</td>
</tr>
</pre>
</div>
<h5 id="div-for">6.1.2 div_for</h5><p>This is actually a convenient method which calls <code>content_tag_for</code> internally with <code>:div</code> as the tag name. You can pass either an Active Record object or a collection of objects. For example:</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
<%= div_for(@article, class: "frontpage") do %>
<td><%= @article.title %></td>
<% end %>
</pre>
</div>
<p>Will generate this HTML output:</p><div class="code_container">
<pre class="brush: xml; gutter: false; toolbar: false">
<div id="article_1234" class="article frontpage">
<td>Hello World!</td>
</div>
</pre>
</div>
<h4 id="assettaghelper">6.2 AssetTagHelper</h4><p>This module provides methods for generating HTML that links views to assets such as images, JavaScript files, stylesheets, and feeds.</p><p>By default, Rails links to these assets on the current host in the public folder, but you can direct Rails to link to assets from a dedicated assets server by setting <code>config.action_controller.asset_host</code> in the application configuration, typically in <code>config/environments/production.rb</code>. For example, let's say your asset host is <code>assets.example.com</code>:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
config.action_controller.asset_host = "assets.example.com"
image_tag("rails.png") # => <img src="http://assets.example.com/images/rails.png" alt="Rails" />
</pre>
</div>
<h5 id="register-javascript-expansion">6.2.1 register_javascript_expansion</h5><p>Register one or more JavaScript files to be included when symbol is passed to javascript_include_tag. This method is typically intended to be called from plugin initialization to register JavaScript files that the plugin installed in <code>vendor/assets/javascripts</code>.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
ActionView::Helpers::AssetTagHelper.register_javascript_expansion monkey: ["head", "body", "tail"]
javascript_include_tag :monkey # =>
<script src="/assets/head.js"></script>
<script src="/assets/body.js"></script>
<script src="/assets/tail.js"></script>
</pre>
</div>
<h5 id="register-stylesheet-expansion">6.2.2 register_stylesheet_expansion</h5><p>Register one or more stylesheet files to be included when symbol is passed to <code>stylesheet_link_tag</code>. This method is typically intended to be called from plugin initialization to register stylesheet files that the plugin installed in <code>vendor/assets/stylesheets</code>.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
ActionView::Helpers::AssetTagHelper.register_stylesheet_expansion monkey: ["head", "body", "tail"]
stylesheet_link_tag :monkey # =>
<link href="/assets/head.css" media="screen" rel="stylesheet" />
<link href="/assets/body.css" media="screen" rel="stylesheet" />
<link href="/assets/tail.css" media="screen" rel="stylesheet" />
</pre>
</div>
<h5 id="auto-discovery-link-tag">6.2.3 auto_discovery_link_tag</h5><p>Returns a link tag that browsers and feed readers can use to auto-detect an RSS or Atom feed.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
auto_discovery_link_tag(:rss, "http://www.example.com/feed.rss", {title: "RSS Feed"}) # =>
<link rel="alternate" type="application/rss+xml" title="RSS Feed" href="http://www.example.com/feed" />
</pre>
</div>
<h5 id="image-path">6.2.4 image_path</h5><p>Computes the path to an image asset in the <code>app/assets/images</code> directory. Full paths from the document root will be passed through. Used internally by <code>image_tag</code> to build the image path.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
image_path("edit.png") # => /assets/edit.png
</pre>
</div>
<p>Fingerprint will be added to the filename if config.assets.digest is set to true.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
image_path("edit.png") # => /assets/edit-2d1a2db63fc738690021fedb5a65b68e.png
</pre>
</div>
<h5 id="image-url">6.2.5 image_url</h5><p>Computes the url to an image asset in the <code>app/assets/images</code> directory. This will call <code>image_path</code> internally and merge with your current host or your asset host.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
image_url("edit.png") # => http://www.example.com/assets/edit.png
</pre>
</div>
<h5 id="image-tag">6.2.6 image_tag</h5><p>Returns an html image tag for the source. The source can be a full path or a file that exists in your <code>app/assets/images</code> directory.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
image_tag("icon.png") # => <img src="/assets/icon.png" alt="Icon" />
</pre>
</div>
<h5 id="javascript-include-tag">6.2.7 javascript_include_tag</h5><p>Returns an html script tag for each of the sources provided. You can pass in the filename (<code>.js</code> extension is optional) of JavaScript files that exist in your <code>app/assets/javascripts</code> directory for inclusion into the current page or you can pass the full path relative to your document root.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
javascript_include_tag "common" # => <script src="/assets/common.js"></script>
</pre>
</div>
<p>If the application does not use the asset pipeline, to include the jQuery JavaScript library in your application, pass <code>:defaults</code> as the source. When using <code>:defaults</code>, if an <code>application.js</code> file exists in your <code>app/assets/javascripts</code> directory, it will be included as well.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
javascript_include_tag :defaults
</pre>
</div>
<p>You can also include all JavaScript files in the <code>app/assets/javascripts</code> directory using <code>:all</code> as the source.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
javascript_include_tag :all
</pre>
</div>
<p>You can also cache multiple JavaScript files into one file, which requires less HTTP connections to download and can better be compressed by gzip (leading to faster transfers). Caching will only happen if <code>ActionController::Base.perform_caching</code> is set to true (which is the case by default for the Rails production environment, but not for the development environment).</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
javascript_include_tag :all, cache: true # =>
<script src="/javascripts/all.js"></script>
</pre>
</div>
<h5 id="javascript-path">6.2.8 javascript_path</h5><p>Computes the path to a JavaScript asset in the <code>app/assets/javascripts</code> directory. If the source filename has no extension, <code>.js</code> will be appended. Full paths from the document root will be passed through. Used internally by <code>javascript_include_tag</code> to build the script path.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
javascript_path "common" # => /assets/common.js
</pre>
</div>
<h5 id="javascript-url">6.2.9 javascript_url</h5><p>Computes the url to a JavaScript asset in the <code>app/assets/javascripts</code> directory. This will call <code>javascript_path</code> internally and merge with your current host or your asset host.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
javascript_url "common" # => http://www.example.com/assets/common.js
</pre>
</div>
<h5 id="stylesheet-link-tag">6.2.10 stylesheet_link_tag</h5><p>Returns a stylesheet link tag for the sources specified as arguments. If you don't specify an extension, <code>.css</code> will be appended automatically.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
stylesheet_link_tag "application" # => <link href="/assets/application.css" media="screen" rel="stylesheet" />
</pre>
</div>
<p>You can also include all styles in the stylesheet directory using :all as the source:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
stylesheet_link_tag :all
</pre>
</div>
<p>You can also cache multiple stylesheets into one file, which requires less HTTP connections and can better be compressed by gzip (leading to faster transfers). Caching will only happen if ActionController::Base.perform_caching is set to true (which is the case by default for the Rails production environment, but not for the development environment).</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
stylesheet_link_tag :all, cache: true
# => <link href="/assets/all.css" media="screen" rel="stylesheet" />
</pre>
</div>
<h5 id="stylesheet-path">6.2.11 stylesheet_path</h5><p>Computes the path to a stylesheet asset in the <code>app/assets/stylesheets</code> directory. If the source filename has no extension, .css will be appended. Full paths from the document root will be passed through. Used internally by stylesheet_link_tag to build the stylesheet path.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
stylesheet_path "application" # => /assets/application.css
</pre>
</div>
<h5 id="stylesheet-url">6.2.12 stylesheet_url</h5><p>Computes the url to a stylesheet asset in the <code>app/assets/stylesheets</code> directory. This will call <code>stylesheet_path</code> internally and merge with your current host or your asset host.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
stylesheet_url "application" # => http://www.example.com/assets/application.css
</pre>
</div>
<h4 id="atomfeedhelper">6.3 AtomFeedHelper</h4><h5 id="atom-feed">6.3.1 atom_feed</h5><p>This helper makes building an Atom feed easy. Here's a full usage example:</p><p><strong>config/routes.rb</strong></p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
resources :articles
</pre>
</div>
<p><strong>app/controllers/articles_controller.rb</strong></p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
def index
@articles = Article.all
respond_to do |format|
format.html
format.atom
end
end
</pre>
</div>
<p><strong>app/views/articles/index.atom.builder</strong></p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
atom_feed do |feed|
feed.title("Articles Index")
feed.updated((@articles.first.created_at))
@articles.each do |article|
feed.entry(article) do |entry|
entry.title(article.title)
entry.content(article.body, type: 'html')
entry.author do |author|
author.name(article.author_name)
end
end
end
end
</pre>
</div>
<h4 id="benchmarkhelper">6.4 BenchmarkHelper</h4><h5 id="benchmark">6.4.1 benchmark</h5><p>Allows you to measure the execution time of a block in a template and records the result to the log. Wrap this block around expensive operations or possible bottlenecks to get a time reading for the operation.</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
<% benchmark "Process data files" do %>
<%= expensive_files_operation %>
<% end %>
</pre>
</div>
<p>This would add something like "Process data files (0.34523)" to the log, which you can then use to compare timings when optimizing your code.</p><h4 id="cachehelper">6.5 CacheHelper</h4><h5 id="cache">6.5.1 cache</h5><p>A method for caching fragments of a view rather than an entire action or page. This technique is useful caching pieces like menus, lists of news topics, static HTML fragments, and so on. This method takes a block that contains the content you wish to cache. See <code>ActionController::Caching::Fragments</code> for more information.</p><div class="code_container">
<pre class="brush: ruby; html-script: true; gutter: false; toolbar: false">
<% cache do %>
<%= render "shared/footer" %>
<% end %>
</pre>
</div>
<h4 id="capturehelper">6.6 CaptureHelper</h4><h5 id="capture">6.6.1 capture</h5><p>The <code>capture</code> method allows you to extract part of a template into a variable. You can then use this variable anywhere in your templates or layout.</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
<% @greeting = capture do %>
<p>Welcome! The date and time is <%= Time.now %></p>
<% end %>
</pre>
</div>
<p>The captured variable can then be used anywhere else.</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
<html>
<head>
<title>Welcome!</title>
</head>
<body>
<%= @greeting %>
</body>
</html>
</pre>
</div>
<h5 id="content-for">6.6.2 content_for</h5><p>Calling <code>content_for</code> stores a block of markup in an identifier for later use. You can make subsequent calls to the stored content in other templates or the layout by passing the identifier as an argument to <code>yield</code>.</p><p>For example, let's say we have a standard application layout, but also a special page that requires certain JavaScript that the rest of the site doesn't need. We can use <code>content_for</code> to include this JavaScript on our special page without fattening up the rest of the site.</p><p><strong>app/views/layouts/application.html.erb</strong></p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
<html>
<head>
<title>Welcome!</title>
<%= yield :special_script %>
</head>
<body>
<p>Welcome! The date and time is <%= Time.now %></p>
</body>
</html>
</pre>
</div>
<p><strong>app/views/articles/special.html.erb</strong></p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
<p>This is a special page.</p>
<% content_for :special_script do %>
<script>alert('Hello!')</script>
<% end %>
</pre>
</div>
<h4 id="datehelper">6.7 DateHelper</h4><h5 id="date-select">6.7.1 date_select</h5><p>Returns a set of select tags (one for year, month, and day) pre-selected for accessing a specified date-based attribute.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
date_select("article", "published_on")
</pre>
</div>
<h5 id="datetime-select">6.7.2 datetime_select</h5><p>Returns a set of select tags (one for year, month, day, hour, and minute) pre-selected for accessing a specified datetime-based attribute.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
datetime_select("article", "published_on")
</pre>
</div>
<h5 id="distance-of-time-in-words">6.7.3 distance_of_time_in_words</h5><p>Reports the approximate distance in time between two Time or Date objects or integers as seconds. Set <code>include_seconds</code> to true if you want more detailed approximations.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
distance_of_time_in_words(Time.now, Time.now + 15.seconds) # => less than a minute
distance_of_time_in_words(Time.now, Time.now + 15.seconds, include_seconds: true) # => less than 20 seconds
</pre>
</div>
<h5 id="select-date">6.7.4 select_date</h5><p>Returns a set of html select-tags (one for year, month, and day) pre-selected with the <code>date</code> provided.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# Generates a date select that defaults to the date provided (six days after today)
select_date(Time.today + 6.days)
# Generates a date select that defaults to today (no specified date)
select_date()
</pre>
</div>
<h5 id="select-datetime">6.7.5 select_datetime</h5><p>Returns a set of html select-tags (one for year, month, day, hour, and minute) pre-selected with the <code>datetime</code> provided.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# Generates a datetime select that defaults to the datetime provided (four days after today)
select_datetime(Time.now + 4.days)
# Generates a datetime select that defaults to today (no specified datetime)
select_datetime()
</pre>
</div>
<h5 id="select-day">6.7.6 select_day</h5><p>Returns a select tag with options for each of the days 1 through 31 with the current day selected.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# Generates a select field for days that defaults to the day for the date provided
select_day(Time.today + 2.days)
# Generates a select field for days that defaults to the number given
select_day(5)
</pre>
</div>
<h5 id="select-hour">6.7.7 select_hour</h5><p>Returns a select tag with options for each of the hours 0 through 23 with the current hour selected.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# Generates a select field for hours that defaults to the hours for the time provided
select_hour(Time.now + 6.hours)
</pre>
</div>
<h5 id="select-minute">6.7.8 select_minute</h5><p>Returns a select tag with options for each of the minutes 0 through 59 with the current minute selected.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# Generates a select field for minutes that defaults to the minutes for the time provided.
select_minute(Time.now + 6.hours)
</pre>
</div>
<h5 id="select-month">6.7.9 select_month</h5><p>Returns a select tag with options for each of the months January through December with the current month selected.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# Generates a select field for months that defaults to the current month
select_month(Date.today)
</pre>
</div>
<h5 id="select-second">6.7.10 select_second</h5><p>Returns a select tag with options for each of the seconds 0 through 59 with the current second selected.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# Generates a select field for seconds that defaults to the seconds for the time provided
select_second(Time.now + 16.minutes)
</pre>
</div>
<h5 id="select-time">6.7.11 select_time</h5><p>Returns a set of html select-tags (one for hour and minute).</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# Generates a time select that defaults to the time provided
select_time(Time.now)
</pre>
</div>
<h5 id="select-year">6.7.12 select_year</h5><p>Returns a select tag with options for each of the five years on each side of the current, which is selected. The five year radius can be changed using the <code>:start_year</code> and <code>:end_year</code> keys in the <code>options</code>.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# Generates a select field for five years on either side of Date.today that defaults to the current year
select_year(Date.today)
# Generates a select field from 1900 to 2009 that defaults to the current year
select_year(Date.today, start_year: 1900, end_year: 2009)
</pre>
</div>
<h5 id="time-ago-in-words">6.7.13 time_ago_in_words</h5><p>Like <code>distance_of_time_in_words</code>, but where <code>to_time</code> is fixed to <code>Time.now</code>.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
time_ago_in_words(3.minutes.from_now) # => 3 minutes
</pre>
</div>
<h5 id="time-select">6.7.14 time_select</h5><p>Returns a set of select tags (one for hour, minute and optionally second) pre-selected for accessing a specified time-based attribute. The selects are prepared for multi-parameter assignment to an Active Record object.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# Creates a time select tag that, when POSTed, will be stored in the order variable in the submitted attribute
time_select("order", "submitted")
</pre>
</div>
<h4 id="debughelper">6.8 DebugHelper</h4><p>Returns a <code>pre</code> tag that has object dumped by YAML. This creates a very readable way to inspect an object.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
my_hash = {'first' => 1, 'second' => 'two', 'third' => [1,2,3]}
debug(my_hash)
</pre>
</div>
<div class="code_container">
<pre class="brush: xml; gutter: false; toolbar: false">
<pre class='debug_dump'>---
first: 1
second: two
third:
- 1
- 2
- 3
</pre>
</pre>
</div>
<h4 id="formhelper">6.9 FormHelper</h4><p>Form helpers are designed to make working with models much easier compared to using just standard HTML elements by providing a set of methods for creating forms based on your models. This helper generates the HTML for forms, providing a method for each sort of input (e.g., text, password, select, and so on). When the form is submitted (i.e., when the user hits the submit button or form.submit is called via JavaScript), the form inputs will be bundled into the params object and passed back to the controller.</p><p>There are two types of form helpers: those that specifically work with model attributes and those that don't. This helper deals with those that work with model attributes; to see an example of form helpers that don't work with model attributes, check the ActionView::Helpers::FormTagHelper documentation.</p><p>The core method of this helper, form_for, gives you the ability to create a form for a model instance; for example, let's say that you have a model Person and want to create a new instance of it:</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
# Note: a @person variable will have been created in the controller (e.g. @person = Person.new)
<%= form_for @person, url: {action: "create"} do |f| %>
<%= f.text_field :first_name %>
<%= f.text_field :last_name %>
<%= submit_tag 'Create' %>
<% end %>
</pre>
</div>
<p>The HTML generated for this would be:</p><div class="code_container">
<pre class="brush: xml; gutter: false; toolbar: false">
<form action="/people/create" method="post">
<input id="person_first_name" name="person[first_name]" type="text" />
<input id="person_last_name" name="person[last_name]" type="text" />
<input name="commit" type="submit" value="Create" />
</form>
</pre>
</div>
<p>The params object created when this form is submitted would look like:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
{"action" => "create", "controller" => "people", "person" => {"first_name" => "William", "last_name" => "Smith"}}
</pre>
</div>
<p>The params hash has a nested person value, which can therefore be accessed with params[:person] in the controller.</p><h5 id="check-box">6.9.1 check_box</h5><p>Returns a checkbox tag tailored for accessing a specified attribute.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# Let's say that @article.validated? is 1:
check_box("article", "validated")
# => <input type="checkbox" id="article_validated" name="article[validated]" value="1" />
# <input name="article[validated]" type="hidden" value="0" />
</pre>
</div>
<h5 id="fields-for">6.9.2 fields_for</h5><p>Creates a scope around a specific model object like form_for, but doesn't create the form tags themselves. This makes fields_for suitable for specifying additional model objects in the same form:</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
<%= form_for @person, url: {action: "update"} do |person_form| %>
First name: <%= person_form.text_field :first_name %>
Last name : <%= person_form.text_field :last_name %>
<%= fields_for @person.permission do |permission_fields| %>
Admin? : <%= permission_fields.check_box :admin %>
<% end %>
<% end %>
</pre>
</div>
<h5 id="file-field">6.9.3 file_field</h5><p>Returns a file upload input tag tailored for accessing a specified attribute.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
file_field(:user, :avatar)
# => <input type="file" id="user_avatar" name="user[avatar]" />
</pre>
</div>
<h5 id="form-for">6.9.4 form_for</h5><p>Creates a form and a scope around a specific model object that is used as a base for questioning about values for the fields.</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
<%= form_for @article do |f| %>
<%= f.label :title, 'Title' %>:
<%= f.text_field :title %><br>
<%= f.label :body, 'Body' %>:
<%= f.text_area :body %><br>
<% end %>
</pre>
</div>
<h5 id="hidden-field">6.9.5 hidden_field</h5><p>Returns a hidden input tag tailored for accessing a specified attribute.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
hidden_field(:user, :token)
# => <input type="hidden" id="user_token" name="user[token]" value="#{@user.token}" />
</pre>
</div>
<h5 id="label">6.9.6 label</h5><p>Returns a label tag tailored for labelling an input field for a specified attribute.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
label(:article, :title)
# => <label for="article_title">Title</label>
</pre>
</div>
<h5 id="password-field">6.9.7 password_field</h5><p>Returns an input tag of the "password" type tailored for accessing a specified attribute.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
password_field(:login, :pass)
# => <input type="text" id="login_pass" name="login[pass]" value="#{@login.pass}" />
</pre>
</div>
<h5 id="radio-button">6.9.8 radio_button</h5><p>Returns a radio button tag for accessing a specified attribute.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# Let's say that @article.category returns "rails":
radio_button("article", "category", "rails")
radio_button("article", "category", "java")