#196 Nested Model Form Part 1

Jan 11, 2010 | 11 minutes | Active Record, Views, Forms

Handling multiple models in a single form is much easier with the accepts_nested_attributes_for method. See how to use this method to handle nested model fields.

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Note: If you are protecting attributes with attr_accessible be certain to add the nested attributes to that (such as questions_attributes and answers_attributes).

          bash
        
rails surveysays
script/generate nifty_layout
script/generate nifty_scaffold survey name:string
script/generate model question survey_id:integer content:text
script/generate model answer question_id:integer content:string
rake db:migrate

          models/survey.rb
        
class Survey < ActiveRecord::Base
  has_many :questions, :dependent => :destroy
  accepts_nested_attributes_for :questions, :reject_if => lambda { |a| a[:content].blank? }, :allow_destroy => true
end

          models/question.rb
        
class Question < ActiveRecord::Base
  belongs_to :survey
  has_many :answers, :dependent => :destroy
  accepts_nested_attributes_for :answers, :reject_if => lambda { |a| a[:content].blank? }, :allow_destroy => true
end

          models/answer.rb
        
class Answer < ActiveRecord::Base
  belongs_to :question
end

          surveys_controller.rb
        
def new
  @survey = Survey.new
  3.times do
    question = @survey.questions.build
    4.times { question.answers.build }
  end
end

          views/surveys/_form.html.erb
        
<%= form_for @survey do |f| %>
  <%= f.error_messages %>
  <p>
    <%= f.label :name %><br />
    <%= f.text_field :name %>
  </p>
  <%= f.fields_for :questions do |builder| %>
    <%= render "question_fields", :f => builder %>
  <% end %>
  <p><%= f.submit "Submit" %></p>
<% end %>

          views/surveys/_question_fields.html.erb
        
<p>
  <%= f.label :content, "Question" %><br />
  <%= f.text_area :content, :rows => 3 %><br />
  <%= f.check_box :_destroy %>
  <%= f.label :_destroy, "Remove Question" %>
</p>
<%= f.fields_for :answers do |builder| %>
  <%= render 'answer_fields', :f => builder %>
<% end %>

          views/surveys/_answer_fields.html.erb
        
<p>
  <%= f.label :content, "Answer" %>
  <%= f.text_field :content %>
  <%= f.check_box :_destroy %>
  <%= f.label :_destroy, "Remove" %>
</p>