render_to_string from a rake task

I want to use a Rake task to cache my sitemap so that requests for sitemap.xml won't take forever. Here's what I have so far:

  @posts = Post.all

  sitemap = render_to_string :template => 'sitemap/sitemap', :l开发者_Go百科ocals => {:posts => @posts}, :layout => false
  Rails.cache.write('sitemap', sitemap)

But when I try to run this, I get an error:

undefined local variable or method `headers' for #<Object:0x100177298>

How can I render a template to a string from within Rake?

---

Here's how I did it:

  av = ActionView::Base.new(Rails::Configuration.new.view_path)
  av.class_eval do
    include ApplicationHelper
  end

  include ActionController::UrlWriter
  default_url_options[:host] = 'mysite.com'

  posts = Post.all

  sitemap = av.render 'sitemap/sitemap', :posts => posts
  Rails.cache.write('sitemap', sitemap)

Note that I converted my template to a partial to make this work

---

There is a post about how to be able to access ActionView::Base methods and context from rake task.

However, this is a monkeypatch. Why not use the rails' cache mechanism to accomplish caching? :)

Later edit: The render_to_string function is defined in ActionController::Base context.

Below is a solution on how to make it work from rake tasks, taken from omninerd.

# In a rake task:
av = ActionView::Base.new(Rails::Configuration.new.view_path)
Rails.cache.write(
  "cache_var", 
  av.render(
    :partial => "view_folder/some_partial", 
    :locals => {:a_var => @some_var}
  )
)

---

Recently I wanted to take a rake task defined like Horace Loeb mentioned and translate it into a self contained background job, but it didn't easily translate.

Here is my implementation for Rails 2.3.x because the Rails 3 implementation I found wouldn't work.

# Public: Template to render views outside the context of a controller.
#
# Useful for rendering views in rake tasks or background jobs when a
# controller is unavailable.
#
# Examples
#
#   template = OfflineTemplate.new(:users)
#   template.render("users/index", :layout => false, :locals => { :users => users })
#
#   template = OfflineTemplate.new(ProjectsHelper, PermissionsHelper)
#   template.render("projects/recent", :projects => recent_projects)
#
class OfflineTemplate
  include ActionController::UrlWriter
  include ActionController::Helpers::ClassMethods

  # Public: Returns the ActionView::Base internal view.
  attr_reader :view

  # Public: Convenience method  to
  delegate :render, :to => :view

  # Public: Initialize an offline template for the current Rails environment.
  #
  # helpers - The Rails helpers to include (listed as symbols or modules).
  def initialize(*helpers)
    helper(helpers + [ApplicationHelper])
    @view = ActionView::Base.new(Rails.configuration.view_path, {}, self)
    @view.class.send(:include, master_helper_module)
  end

  private

  # Internal: Required to use ActionConroller::Helpers.
  #
  # Returns a Module to collect helper methods.
  def master_helper_module
    @master_helper_module ||= Module.new
  end
end

This is available as a gist: https://gist.github.com/1386052.

Then you can use the class above to create an OfflineTemplate to render your views in a rake task:

task :recent_projects => :environment do 
  template = OfflineTemplate.new(ProjectsHelper, PermissionsHelper)
  puts template.render("projects/recent", :projects => recent_projects)
end