Can Rails Routing Helpers (i.e. mymodel_path(model)) be Used in Models?

Question

Say I have a Rails Model called Thing. Thing has a url attribute that can optionally be set to a URL somewhere on the Internet. In view code, I need logic that does the following:

<% if thing.url.blank? %> <%= link_to('Text', thing_path(thing)) %> <% else %> <%= link_to('Text', thing.url) %> <% end %> 

This conditional logic in the view is ugly. Of course, I could build a helper function, which would change the view to this:

<%= thing_link('Text', thing) %> 

That solves the verbosity problem, but I would really prefer having the functionality in the model itself. In which case, the view code would be:

<%= link_to('Text', thing.link) %> 

This, obviously, would require a link method on the model. Here's what it would need to contain:

def link   (self.url.blank?) ? thing_path(self) : self.url end 

To the point of the question, thing_path() is an undefined method inside Model code. I'm assuming it's possible to "pull in" some helper methods into the model, but how? And is there a real reason that routing only operates at the controller and view layers of the app? I can think of lots of cases where model code may need to deal with URLs (integrating with external systems, etc).

Answer 1

In Rails 3 and higher:

Rails.application.routes.url_helpers 

e.g.

Rails.application.routes.url_helpers.posts_path Rails.application.routes.url_helpers.posts_url(:host => "example.com") 

Answer 2

I've found the answer regarding how to do this myself. Inside the model code, just put:

For Rails <= 2:

include ActionController::UrlWriter 

For Rails 3:

include Rails.application.routes.url_helpers 

This magically makes thing_path(self) return the URL for the current thing, or other_model_path(self.association_to_other_model) return some other URL.