render_to_string from a rake task - ruby-on-rails

Question

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', :locals => {: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?

Answer 1

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

Answer 2

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}
)
)

Answer 3

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