Rails 4 render partial for nested attributes without loop - ruby-on-rails

Question

Suppose I have a form like below
<%= form_for #uni, :html => {:multipart => true, :honeypot => true} do |uni_form| %>
<% 3.times { #uni.app.build } %>
<%= uni_form.fields_for :apps do |builder| %>
<%= render 'app', uni_form: builder %>
<% end %>
<% end %>
and my app partial is
<div>
<%= uni_form.label :uni_id, "University" %>
<%= uni_form.collection_select :uni_id, #unis, :id, :name, {:include_blank => true} %>
</div>
Now I want the first form code without the loop. Something like this
<%= form_for #uni, :html => {:multipart => true, :honeypot => true} do |uni_form| %>
<% 3.times { #uni.app.build } %>
<%= render 'app', uni_form: builder %>
<%= render 'app', uni_form: builder %>
<%= render 'app', uni_form: builder %>
<% end %>
How can I do this?

Answer 1

Firstly, don't build your associated objects in your view - do it in your controller:
#app/controllers/unis_controller.rb
class UnisConstroller < ApplicationController
def new
#uni = Uni.new
3.times do
#uni.apps.build
end
end
end
Secondly, the fields_for method is your friend here.
You'll gain what you need by using the following:
#app/views/unis/new.html.erb
<%= form_for #uni, :html => {:multipart => true, :honeypot => true} do |uni_form| %>
<%= uni_form.fields_for :apps do |builder| %>
<%= builder.label :uni_id, "University" %>
<%= builder.collection_select :uni_id, #unis, :id, :name, {:include_blank => true} %>
<% end %>
<% end %>
fields_for takes your model's associated objects and automatically creates the fields you need. There is literally no need to "loop" - fields_for does it for you... if you set it up correctly.
The problem you have is you're building your associated objects at runtime, which is not only inefficient & against convention, but I think it will prevent the form_for from recognizing them (which is what allows fields_for to loop through them).
The above code should fix this for you.