How to create a Wufoo-like (form builder) web application with JQuery and Rails?
var todoList = {};

$.getJSON("/users/123/todolists/456.json", function(data) {
  loadTodoList(data);
  ...
});

function loadTodoList(data) {
  todoList = data.todoList;
}

function saveTodoList() {
  $.ajax({
    type: 'POST',
    url: "/users/123/todolists/456",
    data: JSON.stringify({ todoList: todoList }),
    contentType: 'application/json',
    dataType: 'script', // could be "json", "html" too
    beforeSend: function(xhr){
      xhr.setRequestHeader("X-Http-Method-Override", "put");
    }
  });
}

# TodoListsController
  def show
    @todolist = TodoList.find_by_id(params[:id], :include => [:tasks, ...])
    respond_to do |format|
      format.json do
        render :json => @todolist.to_json
      end
    end
  end

  # TodoList model
  def to_json
    super(:only => :name,
          :include => { :tasks => { :only => [:name, :description, ...],
                                    :include => ... }})
  end