Rails accepts_nested_attributes_for with f.fields_for and AJAX

Question

I'm curious how to properly use accepts_nested_attributes_for and f.fields_for.

views/orders/new.html.erb

<%= form_for @order, html:{role: "form"} do |f| %>

  <%= f.submit "Don't push...", remote: true %>
  <%= f.text_field :invoice %>
  <%= f.text_field :ordered_on %>
  <%= f.text_field :delivered_on %>

  <table  id='order_form'>
    <h3>Details</h3>
    <tbody>
      <%= render 'order_details/details', f: f %>
    </tbody>
    <%= link_to 'add line', new_order_detail_path(company_id: params[:company_id]), remote: true %>
    <%= link_to 'new box', new_box_path, remote: true %>
  </table>

<% end %>

views/order_details/_details.html.erb

<tr class='row0'>
  <%= f.fields_for :order_details, child_index: child_index do |d| %>
    <td><%= d.collection_select :box_id, @boxes, :id, :uid, {},
                                { name: "box_id", class: 'form-control'} %></td>
    <td><%= d.text_field :quantity, class: 'form-control' %></td>
    <td><%= d.text_field :box_price, class: 'form-control' %></td>
    <td><%= d.text_field :cb_price, class: 'form-control' %></td>
    <td><%= d.text_field :mould_fees, class: 'form-control' %></td>
    <td>$$$</td>
  <% end %>
</tr>
<tr class='box0'>
  <td colspan="6">&#8594; <b><%= @b.uid %></b> | length: <%= @b.length %> | width: <%= @b.width %> | height: <%= @b.height %> | weight: <%= @b.weight %></td>
</tr>

controllers/orders_controller.rb (I'm pretty sure this is wrong... any help here would be greatly appreciated)

def create
  @order = Order.create(params[:order])
  if @order.save
    flash[:success] = "Order #{@order.invoice} added!"
    redirect_to current_user      
  else
    render 'orders/new'
  end
end

models/order.rb

class Order < ActiveRecord::Base
  attr_accessible ..., :order_details_attributes
  has_many :order_details
  accepts_nested_attributes_for :order_details
end

The only way I've been able to get the partial to play nice is if I actually call the fields_for as fields_for Order.new.order_details.build. But that doesn't build the nested object at all. I need to use the f.fields_for nomenclature to build the Order, and the OrderDetail. I can only build one, though. Which is my next issue.

See how there are buttons in there? It AJAXs rows into the form. If you click add line, I get

NameError in Order_details#new
Showing D:/Dropbox/Apps/rails_projects/erbv2/app/views/order_details/new.js.erb where line #3 raised:
undefined local variable or method `f' for #<#<Class:0x5cf0a18>:0x5cbd718>

views/orders/add_detail.js.erb

$('#order_form tr.total').before("<%= j render partial: 'orders/details', locals: {f: @f, child_index: @ci} %>")

I don't know how to define f... I checked out [Rails AJAX: My partial needs a FormBuilder instance](https://stackoverflow.com/questions/371147/rails-ajax- my-partial-needs-a-formbuilder-instance) and a few others.

Any suggestions on how I should handle this? Using the code I have here... I was able to create a new order, with an associated order_details, but the box_id didn't save, and the company_id didn't save. I know this is kind of nasty, but I don't know where else to go.

UPDATE

routes:

resources :orders do
  collection { get :add_detail }
end

this is way better than having a separate resource for the details.  I didn't think of this before!

HTML form:

<%= form_for @order, company_id: params[:company_id], html:{role: "form"} do |f| %>
  f. ...
  <%= render partial: 'details', locals: { f: f } %> #first child
  <%= link_to 'add line', add_detail_orders_path(company_id: params[:company_id]), remote: true %> #add subsequent children
<% end %>

Orders Controller:

def add_detail
  @order = Order.build
  @boxes = Company.find(params[:company_id]).boxes
  @b = @boxes.first
  @ci = Time.now.to_i
  respond_with(@order, @boxes, @b, @ci)
end

_details partial

<%= form_for @order do |f| %>
  <%= f.fields_for :order_details, child_index: @ci do |d| %>
    <td><%= d.collection_select :box_id, @boxes, :id, :uid, {},
                                {class: 'form-control'} %></td>
    <td><%= d.text_field :quantity, class: 'form-control' %></td>
    <td><%= d.text_field :box_price, class: 'form-control' %></td>
    <td><%= d.text_field :cb_price, class: 'form-control' %></td>
    <td><%= d.text_field :mould_fees, class: 'form-control' %></td>
    <td>$$$</td>
  <% end %>
<% end %>

Answer

It Is Possible

There's a very, very good tutorial on this here: <http://pikender.in/2013/04/20/child-forms-using-fields_for-through-ajax- rails-way/>

We also recently implemented this type of form on one of our development apps. If you goto & http://emailsystem.herokuapp.com, sign up (free) and click "New Message". The "Subscribers" part uses this technology

BTW we did this manually. Cocoon actually looks really good, and seems to use the same principles as us. There's also a RailsCast, but this only works for single additions (I think)

f.fields_for

The way you do it is to use a series of partials which dynamically build the fields you need. From your code, it looks like you have the fundamentals in place (the form is working), so now it's a case of building several components to handle the AJAX request:

You need to handle the AJAX on the controller (route + controller action)
You need to put your f.fields_for into partials (so they can be called with Ajax)
You need to handle the build functionality in the model

Handling AJAX With The Controller

Firstly, you need to handle the Ajax requests in the controller

To do this, you need to add a new "endpoint" to the routes. This is ours:

 resources :messages, :except => [:index, :destroy] do
    collection do
       get :add_subscriber
    end
 end

The controller action then translates into:

#app/controllers/messages_controller.rb
#Ajax Add Subscriber
def add_subscriber
    @message = Message.build
    render "add_subscriber", :layout => false
end

Add Yourf.fields_for Into Partials

To handle this, you need to put your f.fields_for into partials. Here is the code form our form:

#app/views/resources/_message_subscriber_fields.html.erb
<%= f.fields_for :message_subscribers, :child_index => child_index do |subscriber| %>
    <%= subscriber.collection_select(:subscriber_id, Subscriber.where(:user_id => current_user.id), :id, :name_with_email, include_blank: 'Subscribers') %>
<% end %>

#app/views/messages/add_subscriber.html.erb
<%= form_for @message, :url => messages_path, :authenticity_token => false do |f| %>
        <%= render :partial => "resources/message_subscriber_fields", locals: {f: f, child_index: Time.now.to_i} %>
<% end %>

#app/views/messages/new.html.erb
<% child_index = Time.now.to_i %>
<div id="subscribers">
    <div class="title">Subscribers</div>
    <%= render :partial => "message_subscriber_fields", locals: {f: f, child_index: child_index } %>
</div>

Extend Your Build Functionality To Your Model

To keep things dry, we just created a build function in the model, which we can call each time:

   #Build
    def self.build
       message = self.new
       message.message_subscribers.build
       message
    end

[Child_Index](http://apidock.com/rails/ActionView/Helpers/FormHelper/fields_for#512-Setting- child-index-while-using-nested-attributes-mass-assignment)

Your best friend here is child_index

If you're adding multiple fields, the big problem you'll have is incrementing the [id] of the field (this was the flaw we found with Ryan Bates' tutorial)

The way the first tutorial I posted solved this was to just set the child_index of the new fields with Time.now.to_i. This sets a unique id, and because the actual ID of the new field is irrelevant, you'll be able to add as many fields as you like with it

JQuery

    #Add Subscriber
    $ ->
      $(document).on "click", "#add_subscriber", (e) ->
         e.preventDefault();

         #Ajax
         $.ajax
           url: '/messages/add_subscriber'
           success: (data) ->
               el_to_add = $(data).html()
               $('#subscribers').append(el_to_add)
           error: (data) ->
               alert "Sorry, There Was An Error!"

Rails accepts_nested_attributes_for with f.fields_for and AJAX

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