Action View templates can be written in three ways. If the template file has a .erb (or .rhtml) extension then it uses a mixture of ERb (included in Ruby) and HTML. If the template file has a .builder (or .rxml) extension then Jim Weirich‘s Builder::XmlMarkup library is used. If the template file has a .rjs extension then it will use ActionView::Helpers::PrototypeHelper::JavaScriptGenerator.


You trigger ERb by using embeddings such as <% %>, <% -%>, and <%= %>. The <%= %> tag set is used when you want output. Consider the following loop for names:

  <b>Names of all the people</b>
  <% for person in @people %>
    Name: <%= %><br/>
  <% end %>

The loop is setup in regular embedding tags <% %> and the name is written using the output embedding tag <%= %>. Note that this is not just a usage suggestion. Regular output functions like print or puts won‘t work with ERb templates. So this would be wrong:

  Hi, Mr. <% puts "Frodo" %>

If you absolutely must write from within a function, you can use the TextHelper#concat.

<%- and -%> suppress leading and trailing whitespace, including the trailing newline, and can be used interchangeably with <% and %>.

Using sub templates

Using sub templates allows you to sidestep tedious replication and extract common display structures in shared templates. The classic example is the use of a header and footer (even though the Action Pack-way would be to use Layouts):

  <%= render "shared/header" %>
  Something really specific and terrific
  <%= render "shared/footer" %>

As you see, we use the output embeddings for the render methods. The render call itself will just return a string holding the result of the rendering. The output embedding writes it to the current template.

But you don‘t have to restrict yourself to static includes. Templates can share variables amongst themselves by using instance variables defined using the regular embedding tags. Like this:

  <% @page_title = "A Wonderful Hello" %>
  <%= render "shared/header" %>

Now the header can pick up on the @page_title variable and use it for outputting a title tag:

  <title><%= @page_title %></title>

Passing local variables to sub templates

You can pass local variables to sub templates by using a hash with the variable names as keys and the objects as values:

  <%= render "shared/header", { :headline => "Welcome", :person => person } %>

These can now be accessed in shared/header with:

  Headline: <%= headline %>
  First name: <%= person.first_name %>

If you need to find out whether a certain local variable has been assigned a value in a particular render call, you need to use the following pattern:

  <% if local_assigns.has_key? :headline %>
    Headline: <%= headline %>
  <% end %>

Testing using defined? headline will not work. This is an implementation restriction.

Template caching

By default, Rails will compile each template to a method in order to render it. When you alter a template, Rails will check the file‘s modification time and recompile it.


Builder templates are a more programmatic alternative to ERb. They are especially useful for generating XML content. An XmlMarkup object named xml is automatically made available to templates with a .builder extension.

Here are some basic examples:

  xml.em("emphasized")                              # => <em>emphasized</em>
  xml.em { xml.b("emph & bold") }                   # => <em><b>emph &amp; bold</b></em>
  xml.a("A Link", "href"=>"") # => <a href="">A Link</a>"name"=>"compile", "option"=>"fast")   # => <target option="fast" name="compile"\>
                                                    # NOTE: order of attributes is not specified.

Any method with a block will be treated as an XML markup tag with nested markup in the block. For example, the following:

  xml.div {

would produce something like:

    <h1>David Heinemeier Hansson</h1>
    <p>A product of Danish Design during the Winter of '79...</p>

A full-length RSS example actually used on Basecamp:

  xml.rss("version" => "2.0", "xmlns:dc" => "") do do
      xml.description "Basecamp: Recent items"
      xml.language "en-us"
      xml.ttl "40"

      for item in @recent_items
        xml.item do
          xml.description(item_description(item)) if item_description(item)
          xml.guid(@person.firm.account.url + @recent_items.url(item))
 + @recent_items.url(item))

          xml.tag!("dc:creator", item.author_name) if item_has_creator?(item)

More builder documentation can be found at


JavaScriptGenerator templates end in .rjs. Unlike conventional templates which are used to render the results of an action, these templates generate instructions on how to modify an already rendered page. This makes it easy to modify multiple elements on your page in one declarative Ajax response. Actions with these templates are called in the background with Ajax and make updates to the page where the request originated from.

An instance of the JavaScriptGenerator object named page is automatically made available to your template, which is implicitly wrapped in an ActionView::Helpers::PrototypeHelper#update_page block.

When an .rjs action is called with link_to_remote, the generated JavaScript is automatically evaluated. Example:

  link_to_remote :url => {:action => 'delete'}

The subsequently rendered delete.rjs might look like:

  page.replace_html  'sidebar', :partial => 'sidebar'
  page.remove        "person-#{}"
  page.visual_effect :highlight, 'user-list'

This refreshes the sidebar, removes a person element and highlights the user list.

See the ActionView::Helpers::PrototypeHelper::GeneratorMethods documentation for more details.

Included Modules
Classes and Modules
Class ActionView::Base::ProxyModule
[RW] assigns
[RW] base_path
[RW] controller
[R] helpers
[RW] output_buffer
[RW] template_extension
[W] template_format
[R] view_paths
Public Class methods
     # File actionpack/lib/action_view/base.rb, line 195
195:     def self.cache_template_loading?
196:       ActionController::Base.allow_concurrency || (cache_template_loading.nil? ? !ActiveSupport::Dependencies.load? : cache_template_loading)
197:     end
   # File actionpack/lib/action_view/test_case.rb, line 6
6:     def initialize(*args)
7:       @_rendered = { :template => nil, :partials => }
8:       initialize_without_template_tracking(*args)
9:     end
     # File actionpack/lib/action_view/base.rb, line 209
209:     def self.process_view_paths(value)
211:     end


     # File actionpack/lib/action_view/base.rb, line 191
191:     def self.xss_safe?
192:       false
193:     end
Public Instance methods

Access the current template being rendered. Returns a ActionView::Template object.

     # File actionpack/lib/action_view/base.rb, line 295
295:     def template
296:       @_current_render
297:     end

The format to be used when choosing between multiple templates with the same name but differing formats. See +Request#template_format+ for more details.

     # File actionpack/lib/action_view/base.rb, line 283
283:     def template_format
284:       if defined? @template_format
285:         @template_format
286:       elsif controller && controller.respond_to?(:request)
287:         @template_format = controller.request.template_format.to_sym
288:       else
289:         @template_format = :html
290:       end
291:     end
     # File actionpack/lib/action_view/base.rb, line 239
239:     def view_paths=(paths)
240:       @view_paths = self.class.process_view_paths(paths)
241:       # we might be using ReloadableTemplates, so we need to let them know this a new request
242:       @view_paths.load!
243:     end
with_template(current_template) {|| ...}
     # File actionpack/lib/action_view/base.rb, line 304
304:     def with_template(current_template)
305:       last_template, self.template = template, current_template
306:       yield
307:     ensure
308:       self.template = last_template
309:     end