partials.rb

module ActionView
  # 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.erb" and pass the instance variable @account in as a local variable +account+ to
  # the template for display.
  #
  # In another template for Advertiser#buy, we could have:
  #
  #   <%= render :partial => "account", :locals => { :account => @buyer } %>
  #
  #   <% for ad in @advertisements %>
  #     <%= render :partial => "ad", :locals => { :ad => ad } %>
  #   <% end %>
  #
  # This would first render "advertiser/_account.erb" with @buyer passed in as the local variable +account+, then render
  # "advertiser/_ad.erb" and pass the local variable +ad+ to the template for display.
  #
  # == 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.erb" and pass the local variable +ad+ to the template for display. An iteration counter
  # will automatically be made available to the template with a name of the form +partial_name_counter+. In the case of the
  # example above, the template would be fed +ad_counter+.
  #
  # 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.erb" regardless of which controller this is being called from.
  #
  # == 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>
  #
  # 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.
  module Partials
    private
      def render_partial(partial_path, object_assigns = nil, local_assigns = nil) #:nodoc:
        case partial_path
        when String, Symbol, NilClass
          path, partial_name = partial_pieces(partial_path)
          object = extracting_object(partial_name, object_assigns)
          local_assigns = local_assigns ? local_assigns.clone : {}
          add_counter_to_local_assigns!(partial_name, local_assigns)
          add_object_to_local_assigns!(partial_name, local_assigns, object)

          if logger
            ActionController::Base.benchmark("Rendered #{path}/_#{partial_name}", Logger::DEBUG, false) do
              render("#{path}/_#{partial_name}", local_assigns)
            end
          else
            render("#{path}/_#{partial_name}", local_assigns)
          end
        when Array, ActiveRecord::Associations::AssociationCollection
          if partial_path.any?
            path       = ActionController::RecordIdentifier.partial_path(partial_path.first)
            collection = partial_path
            render_partial_collection(path, collection, nil, object_assigns.value)
          else
            ""
          end
        else
          render_partial(
            ActionController::RecordIdentifier.partial_path(partial_path),
            object_assigns, local_assigns)
        end
      end

      def render_partial_collection(partial_name, collection, partial_spacer_template = nil, local_assigns = nil) #:nodoc:
        collection_of_partials = Array.new
        counter_name = partial_counter_name(partial_name)
        local_assigns = local_assigns ? local_assigns.clone : {}
        collection.each_with_index do |element, counter|
          local_assigns[counter_name] = counter
          collection_of_partials.push(render_partial(partial_name, element, local_assigns))
        end

        return " " if collection_of_partials.empty?

        if partial_spacer_template
          spacer_path, spacer_name = partial_pieces(partial_spacer_template)
          collection_of_partials.join(render("#{spacer_path}/_#{spacer_name}"))
        else
          collection_of_partials.join
        end
      end

      alias_method :render_collection_of_partials, :render_partial_collection

      def partial_pieces(partial_path)
        if partial_path.include?('/')
          return File.dirname(partial_path), File.basename(partial_path)
        else
          return controller.class.controller_path, partial_path
        end
      end

      def partial_counter_name(partial_name)
        "#{partial_variable_name(partial_name)}_counter".intern
      end

      def partial_variable_name(partial_name)
        partial_name.split('/').last.split('.').first.intern
      end

      def extracting_object(partial_name, object_assigns)
        variable_name = partial_variable_name(partial_name)
        if object_assigns.nil?
          controller.instance_variable_get("@#{variable_name}")
        else
          object_assigns
        end
      end

      def add_counter_to_local_assigns!(partial_name, local_assigns)
        counter_name = partial_counter_name(partial_name)
        local_assigns[counter_name] = 1 unless local_assigns.has_key?(counter_name)
      end

      def add_object_to_local_assigns!(partial_name, local_assigns, object)
        variable_name = partial_variable_name(partial_name)
        local_assigns[variable_name] ||=
          if object.is_a?(ActionView::Base::ObjectWrapper)
            object.value
          else
            object
          end || controller.instance_variable_get("@#{variable_name}")
      end
  end
end