Pre-building view cache in Rails

Question

Is there a way to pre-build a page cache without calling the actual page via a http request?

I looked at solutions like this and this, but these don't generate the cache.

I have a relatively complicated view, and want to cache the entire thing. I want to pre-build this cached version in the application so when a user actually hits it, it will already be there.

Thanks

Answer 1

We had a need to do something similar from a rake task -- we had a partial that would need to display a very long list of entities (~700) which were somewhat context specific and which, due to a series of database structure issues and custom sorting criteria, would easily take > 25 seconds to render the first time before going into cache> This would often time out because our HTTP servers were set to terminate HTTP requests with no response after 30 seconds, and pre-caching this custom list was a solution.

What you need to do is create an instance of ActiveController::Base, or of one of your controllers if you need helper methods or other entities, then pass its lookup_context reference to a new instance of ActionView.Renderer.

In our rake task, we did the following

namespace :rake_for_time_consuming_nonsense do
  task :pre_cache_long_list do
    PreCacher.pre_fetch_partials
  end
end

class PreCacher
  def self.pre_fetch_partials
    the_controller = ActionController::Base.new
    # Set any instance variables required by your partial in the controller, 
    # they will be passed to the partial with the view_context reference
    the_controller.instance_variable_set "@cache_key", cache_key
    the_controller.instance_variable_set "@the_object", MyModel.first

    view_renderer = ActionView::Renderer.new the_controller.lookup_context
    view_renderer.render the_controller.view_context, {partial: 'my_model/the_partial', layout: false}
  end
end

This works in Rails 3.2.13.