Rails 3 remote form: How do I specify the content type?

Question

I am using Rails 3.2, I have a form and I want it to be posted via ajax and have the controller return json.

I am using a form_for helper like so:

= form_for(@object, :remote => true, :format => :json) do |f|
....

My objects controller create method looks like this:

  def create
    respond_to do |format|
      if @object.save
         format.html { redirect_to @object }
         format.json { render json: @object, status: :created, location: @object }
      else
        format.html { render action: "new" }
        format.json { render json: @object.errors, status: :unprocessable_entity }
      end
    end
  end

The form is submitting ajaxly as expected. But the controller is returning html, not json!

Inspecting the request with firebug and sure enough the Content-Type http header on the ajax request is being set to application/html.

The documentation around this is pretty sparse, :format => :json seems to just append ".json" to the forms action, not actually modify any http headers.

I've also tried :content_type => :json to no effect.

I can't simply hard code the controller to return json as there are other places where I do want it to return html...

So does anyone know how to tell the controller to render json when using form_for?

Thanks for any help

Pane

What url and method gets rendered in your form tag on the page? – Elva

Post, the complete tag is: <form method="post" id="new_object" data-remote="true" class="new_object" action="/objects" accept-charset="UTF-8"> – Pane

No json here. Did you consider using request.xhr? to distinguish between ajax and normal requests instead of the requested format? – Elva

OK, did a quick test and that seems to be a workaround, for now. Not sure that it is correct - surely the format and the request mechanism should be seperated. What if I want to add another ajax request later on that needs xml? – Pane

Answer 1

You can set the content-type with:

= form_for(@object, :remote => true, :html => {:'data-type' => 'json'})

As described in rails.js line 106.

Purulence

Thank you! Knew I was missing something obvious! :) – Pane

In Rails 4 you can use format: :json (or :format => :json) instead of :html => {:'data-type' => 'json'} – Jacintojack

@JamesMcMahon In Rails 3.2 either. – Diction

not working in my case :( rails 4 form_for remote true not working and I'm getting this error in browser console Resource interpreted as Script but transferred with MIME type text/html actually response is sent in html form instead of js – Kristeenkristel

That sets the dataType attribute on the ajax request, not the contentType. This results in the changing the Accepts header to json for the request. However, the Content-Type will remain unchanged. – Abdel

Answer 2

For Rails 5, the proper way is to set a data attribute data: { type: :json }.

JQuery UJS docs

Hanlon

That's a bit heavy @DavyM. He was just trying to help and actually helped me with his link to the UJS docs. – Bequest