class ActionView::PartialRenderer

Action View Partials

There's also a convenience method for rendering sub templates within the current controller that depends on a single object (we call this kind of sub templates for partials). It relies on the fact that partials should follow the naming convention of being prefixed with an underscore – as to separate them from regular templates that could be rendered on their own.

In a template for Advertiser#account:

<%= render partial: "account" %>

This would render “advertiser/_account.html.erb”.

In another template for Advertiser#buy, we could have:

<%= render partial: "account", locals: { account: @buyer } %>

<% @advertisements.each do |ad| %>
  <%= render partial: "ad", locals: { ad: ad } %>
<% end %>

This would first render “advertiser/_account.html.erb” with @buyer passed in as the local variable account, then render “advertiser/_ad.html.erb” and pass the local variable ad to the template for display.

The :as and :object options

By default ActionView::PartialRenderer doesn't have any local variables. The :object option can be used to pass an object to the partial. For instance:

<%= render partial: "account", object: @buyer %>

would provide the @buyer object to the partial, available under the local variable account and is equivalent to:

<%= render partial: "account", locals: { account: @buyer } %>

With the :as option we can specify a different name for said local variable. For example, if we wanted it to be user instead of account we'd do:

<%= render partial: "account", object: @buyer, as: 'user' %>

This is equivalent to

<%= render partial: "account", locals: { user: @buyer } %>

Rendering a collection of partials

The example of partial use describes a familiar pattern where a template needs to iterate over an array 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 by the same name as the elements contained within. So the three-lined example in “Using partials” can be rewritten with a single line:

<%= render partial: "ad", collection: @advertisements %>

This will render “advertiser/_ad.html.erb” and pass the local variable ad to the template for display. An iteration object will automatically be made available to the template with a name of the form partial_name_iteration. The iteration object has knowledge about which index the current object has in the collection and the total size of the collection. The iteration object also has two convenience methods, first? and last?. In the case of the example above, the template would be fed ad_iteration. For backwards compatibility the partial_name_counter is still present and is mapped to the iteration's index method.

The :as option may be used when rendering partials.

You can specify a partial to be rendered between elements via the :spacer_template option. The following example will render advertiser/_ad_divider.html.erb between each ad partial:

<%= render partial: "ad", collection: @advertisements, spacer_template: "ad_divider" %>

If the given :collection is nil or empty, render will return nil. This will allow you to specify a text which will displayed instead by using this form:

<%= render(partial: "ad", collection: @advertisements) || "There's no ad to be displayed" %>

NOTE: Due to backwards compatibility concerns, the collection can't be one of hashes. Normally you'd also just keep domain objects, like Active Records, in there.

Rendering shared partials

Two controllers can share a set of partials and render them like this:

<%= render partial: "advertisement/ad", locals: { ad: @advertisement } %>

This will render the partial “advertisement/_ad.html.erb” regardless of which controller this is being called from.

Rendering objects that respond to `to_partial_path`

Instead of explicitly naming the location of a partial, you can also let PartialRenderer do the work and pick the proper path by checking `to_partial_path` method.

# @account.to_partial_path returns 'accounts/account', so it can be used to replace:
# <%= render partial: "accounts/account", locals: { account: @account} %>
<%= render partial: @account %>

# @posts is an array of Post instances, so every post record returns 'posts/post' on `to_partial_path`,
# that's why we can replace:
# <%= render partial: "posts/post", collection: @posts %>
<%= render partial: @posts %>

Rendering the default case

If you're not going to be using any of the options like collections or layouts, you can also use the short-hand defaults of render to render partials. Examples:

# Instead of <%= render partial: "account" %>
<%= render "account" %>

# Instead of <%= render partial: "account", locals: { account: @buyer } %>
<%= render "account", account: @buyer %>

# @account.to_partial_path returns 'accounts/account', so it can be used to replace:
# <%= render partial: "accounts/account", locals: { account: @account} %>
<%= render @account %>

# @posts is an array of Post instances, so every post record returns 'posts/post' on `to_partial_path`,
# that's why we can replace:
# <%= render partial: "posts/post", collection: @posts %>
<%= render @posts %>

Rendering partials with layouts

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. Imagine a list with two types of users:

<%# app/views/users/index.html.erb &>
Here's the administrator:
<%= render partial: "user", layout: "administrator", locals: { user: administrator } %>

Here's the editor:
<%= render partial: "user", layout: "editor", locals: { user: editor } %>

<%# app/views/users/_user.html.erb &>
Name: <%= user.name %>

<%# app/views/users/_administrator.html.erb &>
<div id="administrator">
  Budget: $<%= user.budget %>
  <%= yield %>
</div>

<%# app/views/users/_editor.html.erb &>
<div id="editor">
  Deadline: <%= user.deadline %>
  <%= yield %>
</div>

…this will return:

Here's the administrator:
<div id="administrator">
  Budget: $<%= user.budget %>
  Name: <%= user.name %>
</div>

Here's the editor:
<div id="editor">
  Deadline: <%= user.deadline %>
  Name: <%= user.name %>
</div>

If a collection is given, the layout will be rendered once for each item in the collection. For example, these two snippets have the same output:

<%# app/views/users/_user.html.erb %>
Name: <%= user.name %>

<%# app/views/users/index.html.erb %>
<%# This does not use layouts %>
<ul>
  <% users.each do |user| -%>
    <li>
      <%= render partial: "user", locals: { user: user } %>
    </li>
  <% end -%>
</ul>

<%# app/views/users/_li_layout.html.erb %>
<li>
  <%= yield %>
</li>

<%# app/views/users/index.html.erb %>
<ul>
  <%= render partial: "user", layout: "li_layout", collection: users %>
</ul>

Given two users whose names are Alice and Bob, these snippets return:

<ul>
  <li>
    Name: Alice
  </li>
  <li>
    Name: Bob
  </li>
</ul>

The current object being rendered, as well as the object_counter, will be available as local variables inside the layout template under the same names as available in the partial.

You can also apply a layout to a block within any template:

<%# app/views/users/_chief.html.erb &>
<%= render(layout: "administrator", locals: { user: chief }) do %>
  Title: <%= chief.title %>
<% end %>

…this will return:

<div id="administrator">
  Budget: $<%= user.budget %>
  Title: <%= chief.name %>
</div>

As you can see, the :locals hash is shared between both the partial and its layout.

If you pass arguments to “yield” then this will be passed to the block. One way to use this is to pass an array to layout and treat it as an enumerable.

<%# app/views/users/_user.html.erb &>
<div class="user">
  Budget: $<%= user.budget %>
  <%= yield user %>
</div>

<%# app/views/users/index.html.erb &>
<%= render layout: @users do |user| %>
  Title: <%= user.title %>
<% end %>

This will render the layout for each user and yield to the block, passing the user, each time.

You can also yield multiple times in one layout and use block arguments to differentiate the sections.

<%# app/views/users/_user.html.erb &>
<div class="user">
  <%= yield user, :header %>
  Budget: $<%= user.budget %>
  <%= yield user, :footer %>
</div>

<%# app/views/users/index.html.erb &>
<%= render layout: @users do |user, section| %>
  <%- case section when :header -%>
    Title: <%= user.title %>
  <%- when :footer -%>
    Deadline: <%= user.deadline %>
  <%- end -%>
<% end %>

Constants

IDENTIFIER_ERROR_MESSAGE
OPTION_AS_ERROR_MESSAGE
PREFIXED_PARTIAL_NAMES

Public Class Methods

new(*) click to toggle source
Calls superclass method
# File lib/action_view/renderer/partial_renderer.rb, line 287
def initialize(*)
  super
  @context_prefix = @lookup_context.prefixes.first
end

Public Instance Methods

render(context, options, block) click to toggle source
# File lib/action_view/renderer/partial_renderer.rb, line 292
def render(context, options, block)
  setup(context, options, block)
  identifier = (@template = find_partial) ? @template.identifier : @path

  @lookup_context.rendered_format ||= begin
    if @template && @template.formats.present?
      @template.formats.first
    else
      formats.first
    end
  end

  if @collection
    instrument(:collection, :identifier => identifier || "collection", :count => @collection.size) do
      render_collection
    end
  else
    instrument(:partial, :identifier => identifier) do
      render_partial
    end
  end
end

Private Instance Methods

collection_from_object() click to toggle source
# File lib/action_view/renderer/partial_renderer.rb, line 408
def collection_from_object
  @object.to_ary if @object.respond_to?(:to_ary)
end
collection_from_options() click to toggle source
# File lib/action_view/renderer/partial_renderer.rb, line 401
def collection_from_options
  if @options.key?(:collection)
    collection = @options[:collection]
    collection.respond_to?(:to_ary) ? collection.to_ary : []
  end
end
collection_with_template() click to toggle source
# File lib/action_view/renderer/partial_renderer.rb, line 421
def collection_with_template
  view, locals, template = @view, @locals, @template
  as, counter, iteration = @variable, @variable_counter, @variable_iteration

  if layout = @options[:layout]
    layout = find_template(layout, @template_keys)
  end

  partial_iteration = PartialIteration.new(@collection.size)
  locals[iteration] = partial_iteration

  @collection.map do |object|
    locals[as]        = object
    locals[counter]   = partial_iteration.index

    content = template.render(view, locals)
    content = layout.render(view, locals) { content } if layout
    partial_iteration.iterate!
    content
  end
end
collection_without_template() click to toggle source
# File lib/action_view/renderer/partial_renderer.rb, line 443
def collection_without_template
  view, locals, collection_data = @view, @locals, @collection_data
  cache = {}
  keys  = @locals.keys

  partial_iteration = PartialIteration.new(@collection.size)

  @collection.map do |object|
    index = partial_iteration.index
    path, as, counter, iteration = collection_data[index]

    locals[as]        = object
    locals[counter]   = index
    locals[iteration] = partial_iteration

    template = (cache[path] ||= find_template(path, keys + [as, counter]))
    content = template.render(view, locals)
    partial_iteration.iterate!
    content
  end
end
find_partial() click to toggle source
# File lib/action_view/renderer/partial_renderer.rb, line 412
def find_partial
  find_template(@path, @template_keys) if @path
end
find_template(path, locals) click to toggle source
# File lib/action_view/renderer/partial_renderer.rb, line 416
def find_template(path, locals)
  prefixes = path.include?(?/) ? [] : @lookup_context.prefixes
  @lookup_context.find_template(path, prefixes, true, locals, @details)
end
merge_prefix_into_object_path(prefix, object_path) click to toggle source
# File lib/action_view/renderer/partial_renderer.rb, line 492
def merge_prefix_into_object_path(prefix, object_path)
  if prefix.include?(?/) && object_path.include?(?/)
    prefixes = []
    prefix_array = File.dirname(prefix).split('/')
    object_path_array = object_path.split('/')[0..-3] # skip model dir & partial

    prefix_array.each_with_index do |dir, index|
      break if dir == object_path_array[index]
      prefixes << dir
    end

    (prefixes << object_path).join("/")
  else
    object_path
  end
end
partial_path(object = @object) click to toggle source

Obtains the path to where the object's partial is located. If the object responds to to_partial_path, then to_partial_path will be called and will provide the path. If the object does not respond to to_partial_path, then an ArgumentError is raised.

If prefix_partial_path_with_controller_namespace is true, then this method will prefix the partial paths with a namespace.

# File lib/action_view/renderer/partial_renderer.rb, line 472
def partial_path(object = @object)
  object = object.to_model if object.respond_to?(:to_model)

  path = if object.respond_to?(:to_partial_path)
    object.to_partial_path
  else
    raise ArgumentError.new("'#{object.inspect}' is not an ActiveModel-compatible object. It must implement :to_partial_path.")
  end

  if @view.prefix_partial_path_with_controller_namespace
    prefixed_partial_names[path] ||= merge_prefix_into_object_path(@context_prefix, path.dup)
  else
    path
  end
end
prefixed_partial_names() click to toggle source
# File lib/action_view/renderer/partial_renderer.rb, line 488
def prefixed_partial_names
  @prefixed_partial_names ||= PREFIXED_PARTIAL_NAMES[@context_prefix]
end
raise_invalid_identifier(path) click to toggle source
# File lib/action_view/renderer/partial_renderer.rb, line 540
def raise_invalid_identifier(path)
  raise ArgumentError.new(IDENTIFIER_ERROR_MESSAGE % (path))
end
raise_invalid_option_as(as) click to toggle source
# File lib/action_view/renderer/partial_renderer.rb, line 544
def raise_invalid_option_as(as)
  raise ArgumentError.new(OPTION_AS_ERROR_MESSAGE % (as))
end
render_collection() click to toggle source
# File lib/action_view/renderer/partial_renderer.rb, line 317
def render_collection
  return nil if @collection.blank?

  if @options.key?(:spacer_template)
    spacer = find_template(@options[:spacer_template], @locals.keys).render(@view, @locals)
  end

  result = @template ? collection_with_template : collection_without_template
  result.join(spacer).html_safe
end
render_partial() click to toggle source
# File lib/action_view/renderer/partial_renderer.rb, line 328
def render_partial
  view, locals, block = @view, @locals, @block
  object, as = @object, @variable

  if !block && (layout = @options[:layout])
    layout = find_template(layout.to_s, @template_keys)
  end

  object = locals[as] if object.nil? # Respect object when object is false
  locals[as] = object

  content = @template.render(view, locals) do |*name|
    view._layout_for(*name, &block)
  end

  content = layout.render(view, locals){ content } if layout
  content
end
retrieve_template_keys() click to toggle source
# File lib/action_view/renderer/partial_renderer.rb, line 509
def retrieve_template_keys
  keys = @locals.keys
  keys << @variable if @has_object || @collection
  if @collection
    keys << @variable_counter
    keys << @variable_iteration
  end
  keys
end
retrieve_variable(path, as) click to toggle source
# File lib/action_view/renderer/partial_renderer.rb, line 519
def retrieve_variable(path, as)
  variable = as || begin
    base = path[-1] == "/" ? "" : File.basename(path)
    raise_invalid_identifier(path) unless base =~ /\A_?([a-z]\w*)(\.\w+)*\z/
    $1.to_sym
  end
  if @collection
    variable_counter = :"#{variable}_counter"
    variable_iteration = :"#{variable}_iteration"
  end
  [variable, variable_counter, variable_iteration]
end
setup(context, options, block) click to toggle source

Sets up instance variables needed for rendering a partial. This method finds the options and details and extracts them. The method also contains logic that handles the type of object passed in as the partial.

If +options+ is a string, then the +@path+ instance variable is set to that string. Otherwise, the +options+ object must respond to to_partial_path in order to setup the path.

# File lib/action_view/renderer/partial_renderer.rb, line 356
def setup(context, options, block)
  @view   = context
  @options = options
  @block   = block

  @locals  = options[:locals] || {}
  @details = extract_details(options)

  prepend_formats(options[:formats])

  partial = options[:partial]

  if String === partial
    @has_object = options.key?(:object)
    @object     = options[:object]
    @collection = collection_from_options
    @path       = partial
  else
    @has_object = true
    @object = partial
    @collection = collection_from_object || collection_from_options

    if @collection
      paths = @collection_data = @collection.map { |o| partial_path(o) }
      @path = paths.uniq.one? ? paths.first : nil
    else
      @path = partial_path
    end
  end

  if as = options[:as]
    raise_invalid_option_as(as) unless as.to_s =~ /\A[a-z_]\w*\z/
    as = as.to_sym
  end

  if @path
    @variable, @variable_counter, @variable_iteration = retrieve_variable(@path, as)
    @template_keys = retrieve_template_keys
  else
    paths.map! { |path| retrieve_variable(path, as).unshift(path) }
  end

  self
end