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).

Solution 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")

Solution 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.

Solution 3

You may also find the following approach cleaner than including every method:

class Thing
  delegate :url_helpers, to: 'Rails.application.routes' 

  def url
    url_helpers.thing_path(self)
  end
end

Solution 4

Any logic having to do with what is displayed in the view should be delegated to a helper method, as methods in the model are strictly for handling data.

Here is what you could do:

# In the helper...

def link_to_thing(text, thing)
  (thing.url?) ? link_to(text, thing_path(thing)) : link_to(text, thing.url)
end

# In the view...

<%= link_to_thing("text", @thing) %>

Solution 5

I really like following clean solution.

class Router
  include Rails.application.routes.url_helpers

  def self.default_url_options
    ActionMailer::Base.default_url_options
  end
end

router = Router.new
router.posts_url  # http://localhost:3000/posts
router.posts_path # /posts

It's from http://hawkins.io/2012/03/generating_urls_whenever_and_wherever_you_want/

View more solutions

Comments

[Josh Delsman]

Say you have an Image model. If the Image has an associated outside URL with it, then point to that URL. Otherwise, point to the Image's show page to upload an image? Just an idea.

[Aaron Longwell]

Re: "Unless the model is returning a URL as a piece of data". That's exactly what is happening here... the Model "owns" this piece of data, which is either a link to an on-site or off-site URL. In some cases the URL is generated from Rails Routing. In other cases, the URL is user-supplied data.

[Aaron Longwell]

How about this less generic example: link_to "Full Size Image", image.link The link method in the model would either link to the on-site URL (image_path), or to, say, a Flickr URL if the user provided one and .url was set on the image.

[Aaron Longwell]

What I don't like about helper methods in this case: When I look at link_to_thing(), I have to decide whether that's a thing-specific or application-wide helper (it easily could be either). I need to consider checking 2 files for the source. thing.link leaves no question about the source file.

[Aaron Longwell]

Also, what if I need to use this functionality in a Rake task (to export a CSV file of thing URLs perhaps)... going directly to the model would be much better in that case as well.

[Josh Delsman]

But the difference is that the link_to wouldn't be available in the model, since it is an ActionView helper. So, this would not work. You could hack some attribute defaults in the model, so if it isn't set, it defaults to something, but that's up to you.

[JasonSmith]

With web services APIs growing, often times models need to contact external resources with their own data and provide callback URLs. For example, a photo object needs to post itself to Socialmod, which will call back to that photo's URL when moderation is performed. An after_create() hook would make sense to post to Socialmod, but how do you know the callback URL? I think the author's own answer makes good sense.

[Viacheslav Molokov]

Ypu can include this into any module and after it you can access url-helpers there. Thx

[Windix]

Just an update, since the above is deprecated. This is the current include:include Rails.application.routes.url_helpers

[tlbrack]

Documentation on this seemed hard to find, so here is a decent link regarding the use of delegate in ActiveSupport. simonecarletti.com/blog/2009/12/inside-ruby-on-rails-delegat‌​e

[nitecoder]

Whilst you are right in strictly technical sense, there are times when people just need things to work without having to shave every yak there is to avoid violating some sacred design pattern or what have you, maybe they need to get the url, and actually store it in the database, would be handy then for a model to just know how to do that instead of passing things back and forth, sometimes rules can be broken.

[Augustin Riedinger]

I get a undefined local variable or method 'url_helpers' for Event:Class error... :(

[Mike]

Save yourself from copying your :host option everywhere and set it once in your environment config files: Rails.application.routes.default_url_options[:host] = 'localhost:3000'

[cevaris]

Rails.application.routes.url_helpers worked for me on Rails 4

[spyle]

In Rails v3.2.18 I was able to add self.routes.default_url_options[:host] = 'www.example.com' to my config/application.rb to have it available everywhere. Probably could move it into the the config/environments/*.rb files to customize it for each environment mode.

[Jan]

include Rails.application.routes.url_helpers works for me in Rails 4.1

[trueinViso]

If you just need the path you can use :only_path => true as an option without passing the host parameter.

[Draiken]

If you need to break the rules for a simple model know his url... well, something is really broken in your code.

[moger777]

I get NoMethodError (undefined method `optimize_routes_generation?' for #<ActionView::Base:0x007fe8c0eecbd0>) when I try this

[Renars Sirotins]

this seems to be good option: hawkins.io/2012/03/…

[asiniy]

I get undefined method url_helpers. What I gonna do?

[Ryan]

It looks like in Rails 4.2, you have define default_url_options locally in the model. @RenarsSirotins link worked well for me and makes it DRY.

[Krzysztof Witczak]

@asiniy, are You sure You've used delegate option to url_helpers that is written after class declaration?

[Peter DeWeese]

Works in Rails 5.1.5 for me.

[skplunkerin]

Doesn't work, but it might be that this only works if you create your own class, as shown in the answer. If your Model class already extends < ApplicationRecord this won't work?