Rails 3 nested models

Question

I'm trying to understand how to nest models with rails (active records to then apply it to my project with mongodb)

I'm following this railscast tutorial:

http://railscasts.com/episodes/196-nested-model-form-part-1

but i'm stuck at the beginning when I can't display the form to add new questions to the survey.

I have set up the relationships in the models

models/survey.erb:

class Survey < ActiveRecord::Base
  has_many :questions, :dependent => :destroy
  accepts_nested_attributes_for :questions
  validates_presence_of :name
end

models/question.erb:

class Question < ActiveRecord::Base
  belongs_to :survey
  validates_presence_of :content
end

controllers/surveys_controller.rb:

def new
  @survey = Survey.new
  @survey.questions.build

  respond_to do |format|
    format.html # new.html.erb
    format.json { render json: @survey }
  end
end

views/survey/_form.html.erb"

<%= form_for(@survey) do |f| %>
  <% if @survey.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@survey.errors.count, "error") %> prohibited this survey from being saved:</h2>

      <ul>
      <% @survey.errors.full_messages.each do |msg| %>
        <li><%= msg %></li>
      <% end %>
      </ul>
    </div>
  <% end %>

  <div class="field">
    <%= f.label :name %><br />
    <%= f.text_field :name %>
  </div>
  <h3>Add new question</h3>
  <% f.fields_for :questions do |p| %>
    <%= p.label :content, "Questions" %><br />
    <%= p.text_area :content, :rows => 3 %>
  <% end %>
  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>

but when I try to build the nested form, it doesn't work. I don't get any errors but the form doesn't show.

Am i missing something?

Dylan Markow · Accepted Answer · 2011-11-06 19:17:52Z

1

You should be using a <%=, not a <% on your field_for line, similar to your form_for line. Otherwise, the actual nested form won't get displayed.

<%= f.fields_for :questions do |p| %>

answered Nov 6, 2011 at 19:17

Dylan Markow

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1 Comment

Yannick Schall Over a year ago

Thanks for that. I got confused with something that I read recently. Control logic don't need <%= in rails if it doesn't output code. So I thought that the field_for was a control thingy to output the inner code :(

Tilo · Accepted Answer · 2011-11-06 20:34:22Z

1

You are not taking full advantage of the nested forms in your example.

To DRY things up you should replace the form_for(@survey) by nested_form_for(@survey)

and then you can pull out the questions sub-form into it's own partial, and just do a:

f.fields_for :questions   # without a block

and handle the questions form under ./app/views/questions/_form.html.erb as a regular form_for(@question)

This way you don't have to duplicate code for the questions form inside your survey form.

P.S.: You will need to add "nested_form" Gem to your Gemfile.

edited Nov 6, 2011 at 20:34

answered Nov 6, 2011 at 20:06

Tilo

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2 Comments

Yannick Schall Over a year ago

but that's a gem or is part of rails?

Tilo Over a year ago

It's a Gem, called "nested_from" -- you'll need to add it to your Gemfile

tttthet · Accepted Answer · 2012-07-30 20:08:12Z

0

Just in case anyone else get's stuck on this and winds up here, like me, this issue is the missing '=' in the fields_for call's brackets: '<%= f.fields_for...'

answered Jul 30, 2012 at 20:08

tttthet

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