在Rails中构建自定义ajax表单时，要发送给控制器以使其响应Json的正确数据是什么？

Question

I want to build a custom ajax form (not interested in using the Rails out of the box solution):

    $('form.ajaxForm').submit(function(e){
        e.preventDefault();
        var $form = $(this),
          formValues = getFormValues($form),
          formUrl = $form.attr('action');


        $.post(formUrl, {
          data : formValues,
          contentType: "application/json",
          success : function(data, textStatus, jqXHR){
             // do success here
          }
        });
      });

var getFormValues = function($form){
    var values = {};
    var valuesArray = $form.serializeArray();
    for(var i = 0, max = valuesArray.length; i < max; i++){
      var value = valuesArray[i];
      values[value.name] = value.value
    };
    return values;
  };

I do want to use Rails 3's ability to respond differently when it receives a json request such as:

def create
    @registration = Registration.new(params[:registration])

    respond_to do |format|
      format.html { render action: "new" }
      format.json { render json: @registration.errors, status: :unprocessable_entity }
    end
  end

For some reason, Rails cant process my request during the post, and doesn't respond to json. What in the http headers tells it to respond to json, and what is the proper way to post this data?

Answer 1

Looking at the Rails API docs I came across this tidbit:

Rails determines the desired response format from the HTTP Accept header submitted by the client.

jQuery's $.ajax call has an accepts setting that can be used to set the value for this header but I believe that using dataType will automatically configure this for you.