Question

I have the following in my routes.rb

map.diff 'posts/:id/diff/:from/:to', :controller => "posts",
                   :action => "diff", :conditions => { :method => :get }

And I have the following in my view file.

- form_tag(diff_path(), :method => :get) do
  = text_field_tag(:from, "")
  = text_field_tag(:to, "")
  = hidden_field_tag(:id, @post.id)
  = submit_tag("Submit")

I would like to generate a form that submits something like “http://example.com/posts/3/diff/13/18“, but it fails. How can I make such a form?

I need to pass parameters for diff_path(), but I don’t know how to do that. I don’t even know if this is possible with form_tag.

The error message:

diff_url failed to generate from {:action=>"diff", :controller=>"posts"} - you may have ambiguous routes, or you may need to supply additional parameters for this route.  content_url has the following required parameters: ["posts", :id, "diff", :from, :to] - are they all satisfied?

Answer 1

To my knowledge, what you’re trying to accomplish can’t be done with just an HTML form. The reason being that the form will only know how to submit traditionally via GET and POST. It has no knowledge of the structure of the URL.

You get that error message because the :id, :from and :to parameters are required to form the both you want, so when you call diff_path() it freaks out.

Personally, I would advise you not to use the URL structure you’re planning on – however I’m not totally clear on what this page is going to display. Regardless, if the :from and :to parameters are algorithmic input and not resource identifiers, I would avoid this structure.

That said, if you do want to implement this, you would either have to implement a redirect from rails or javascript.

---

Rails method

#some_controller.rb
redirect_to diff_path(:from => params[:from], :to => params[:to])

---

Javascript (jQuery) method

$(function() {
  $("form#your_form_id_here").submit(function() {
    window.location = "posts/" + this.id + "/diff/" + this.from + "/" + this.to;
    return false;
  });
});