Action View Base
Action View templates can be written in several ways. If the template file has a .erb
extension, then it uses the erubi template system which can embed Ruby into an HTML document. If the template file has a .builder
extension, then Jim Weirich's Builder::XmlMarkup library is used.
ERB
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>
<% @people.each do |person| %>
Name: <%= person.name %><br/>
<% end %>
The loop is set up 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:
<%# WRONG %>
Hi, Mr. <% puts "Frodo" %>
If you absolutely must write from within a function use concat
.
When on a line that only contains whitespaces except for the tag, <% %>
suppresses leading and trailing whitespace, including the trailing newline. <% %>
and <%- -%>
are the same. Note however that <%= %>
and <%= -%>
are different: only the latter removes trailing whitespaces.
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 %>
The local variables passed to sub templates can be accessed as a hash using the local_assigns
hash. This lets you access the variables as:
Headline: <%= local_assigns[:headline] %>
This is useful in cases where you aren't sure if the local variable has been assigned. Alternatively, you could also use defined? headline
to first check if the variable has been assigned before using it.
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 in development mode.
Builder
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 & bold</b></em>
xml.a("A Link", "href" => "http://onestepback.org") # => <a href="http://onestepback.org">A Link</a>
xml.target("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 do
xml.h1(@person.name)
xml.p(@person.bio)
end
would produce something like:
<div>
<h1>David Heinemeier Hansson</h1>
<p>A product of Danish Design during the Winter of '79...</p>
</div>
Here is a full-length RSS example actually used on Basecamp:
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"
@recent_items.each do |item|
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
For more information on Builder please consult the source code.
- #
- C
- I
Attributes
[R] | lookup_context | |
[R] | view_renderer |
Class Public methods
cache_template_loading() Link
cache_template_loading=(value) Link
inspect() Link
Instance Public methods
_run(method, template, locals, buffer, add_to_stack: true, &block) Link
# File actionview/lib/action_view/base.rb, line 243 def _run(method, template, locals, buffer, add_to_stack: true, &block) _old_output_buffer, _old_virtual_path, _old_template = @output_buffer, @virtual_path, @current_template @current_template = template if add_to_stack @output_buffer = buffer public_send(method, locals, buffer, &block) ensure @output_buffer, @virtual_path, @current_template = _old_output_buffer, _old_virtual_path, _old_template end
compiled_method_container() Link
# File actionview/lib/action_view/base.rb, line 252 def compiled_method_container raise NotImplementedError, <<~msg.squish Subclasses of ActionView::Base must implement `compiled_method_container` or use the class method `with_empty_template_cache` for constructing an ActionView::Base subclass that has an empty cache. msg end
in_rendering_context(options) Link
# File actionview/lib/action_view/base.rb, line 260 def in_rendering_context(options) old_view_renderer = @view_renderer old_lookup_context = @lookup_context if !lookup_context.html_fallback_for_js && options[:formats] formats = Array(options[:formats]) if formats == [:js] formats << :html end @lookup_context = lookup_context.with_prepended_formats(formats) @view_renderer = ActionView::Renderer.new @lookup_context end yield @view_renderer ensure @view_renderer = old_view_renderer @lookup_context = old_lookup_context end