Set params hash value using link_to without affecting url in Rails 4

Question

When I submit a form, a number of parameters are set without showing up in the url.

I would like to do the same thing with link_to:

<%= link_to((purchase.paid ? 'yes' : 'no'), {action: :index, hidden_id: purchase.id}) %>

produces the url 'http://localhost:3000/purchases?hidden_id=1'. I would like to link to the url 'http://localhost:3000/purchases' while still setting params[:hidden_id] so I can access it in the controller, as if I had submitted a form.

My routes.rb file is as follows:

root to: 'products#index'
resources :products 
resources :purchases
match ':controller/(:action/(:id))', controller: :shop, via: [:get,:post]

In answering this, is there anything I should know here about the difference in the way these two things are handled? Is it something about get vs post requests or is there some other principle involved which I'm not grasping?

Answer 1

Yes, it's to do with Get vs Post requests.

A Get request can only send parameters in the URL itself. A post request can also be sent to a URL that includes parameters in the URL itself, but it can also send parameters 'under the hood' so to speak.

So if your routes were set up to allow it, you could send either a get or a post request to http://localhost:3000/purchases?hidden_id=1, but only the post request could include additional parameters under the hood.

Anything else you should know about the difference in the way these two are handled? Yes. In most web frameworks, when you see the parameters server-side, they will be split up into GET params and POST params. Rails doesn't make this distinction, and puts them both in the same params hash. (I think this is silly, but whatever).

Also, a get request can be sent simply by entering the URL in your browser and hitting enter. A post request will generally only be executed by a user submitting a form on a web page. For this reason, get requests are not meant to change any content in your database. They should be for viewing information only. So, eg, if you have a button to delete a resource (eg. a blog post or something) it should be submitted via post. (more info on that at Why shouldn't data be modified on an HTTP GET request?)

Lastly, Rails provides an option in it's link_to helper to allow you to easily make the 'link' use a post request. See the method option at http://api.rubyonrails.org/classes/ActionView/Helpers/UrlHelper.html#method-i-link_to. This basically uses javascript to prevent the normal action of clicking the link (which would be a get request), and submit a post request instead.