Accessing Nested Model Attributes Inside a Fields_For Without Using Formbuilder

Accessing nested model attributes inside a fields_for without using FormBuilder

You can call

f.object

to get to the object that the form is associated with.

Accessing nested model attributes inside a fields_for without using FormBuilder

You can call

f.object

to get to the object that the form is associated with.

How to omit existing child records in a nested form in rails?

You can use new_record? method to distinguish between newly created record and old one:

<% form_for @user do |f| %>
   <% f.fields_for :project do |project_form| %>
      <%= render :partial => 'project', :locals => {:f => project_form} if project_form.object.new_record? %>
   <% end %>
   <%= add_child_link "New Project", f, :projects %>
   <%= f.submit "save" %> 
<% end %>

Creating a nested model form

One way to achieve the desired result is that you can craft a form that takes advantage of nested attributes support in Rails:

<%= form_for(@user) do |f| %>
  <%= f.label :my_user_attribute %>
  <%= f.text_field :my_user_attribute %>

  <%= f.fields_for :profile do |fp| %>
    <p>
      <%= fp.label :my_profile_attribute %>
      <%= fp.text_field :my_profile_attribute %>
    </p>
  <% end %>    

  <%= f.submit %>
<% end %>

You will also need to add the following to your User class:

accepts_nested_attributes_for :profile

You can read more about Active Record Nested Attributes here.
You can read more about the ActionView Form Helpers here (search down the page for "Nested Attributes Examples").

If you use this approach, along with good validations on both models, you won't have to worry about tracking the database IDs, because both will be created at the same time by ActiveRecord (but not until both model objects are valid).

Rails accepts_nested_attributes_for with f.fields_for and AJAX

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:

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

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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 Your f.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

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 many-to-many fields_for: How to access fields_for values?

The FormBuilder has attribute accessors like :object_name and :object.

For your particular issue try using:
<%= specform.object.name %>

Rendering nested form fields in Rails

I'm not sure if I've understood what you're asking but if you just want an access to the current item being automatically iterated via simple_fields_for, then you can access it through the form builder as p.object.

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