Uninitialized content when trying to include ActionController::UrlWriter in model

问题

I'm using Rails 3 beta 4 and trying to include ActionController::UrlWriter in my model, which is the correct way to go about it as far as i can tell, but i get "Uninitialized Constant ActionController::UrlWriter".

Any idea why that would be? Did it move in rails 3?

回答1:

First I agree with zed. This shouldn't be done in a model. Your models should be unaware of any http url.

I do the same in a resque job. Here's what I do :

include ActionDispatch::Routing::UrlFor
include ActionController::PolymorphicRoutes
include Rails.application.routes.url_helpers
default_url_options[:host] = 'example.com'

Then you can call any usual url generator.

url_for(object)
page_url(object)

It'll create the link on the host defined as default_url_options[:host]

回答2:

Answers to Can Rails Routing Helpers (i.e. mymodel_path(model)) be Used in Models? are pretty good

or see

http://api.rubyonrails.org/classes/ActionDispatch/Routing/UrlFor.html

http://siddharth-ravichandran.com/2010/11/26/including-url-helpers-in-models/

Basically, you can do something like this in a model:

def url
  Rails.application.routes.url_helpers.download_attachment_path(self)
end

It is worth considering whether this is the right layer, though. In my case it's for file attachments and I want to do attachment.url instead of writing out a helper a lot.

来源：https://stackoverflow.com/questions/3011834/uninitialized-content-when-trying-to-include-actioncontrollerurlwriter-in-mode