RoR nested attributes produces duplicates when edit

Question

I'm trying to follow Ryan Bates RailsCast #196: Nested model form part 1. There're two apparent differences to Ryans version: 1) I'm using built-in scaffolding and not nifty as he's using, and 2) I'm running rails 4 (I don't really know what version Ryans using in his cast, but it's not 4).

So here's what I did

rails new survey2 cd survey2 bundle install rails generate scaffold survey name:string rake db:migrate rails generate model question survey_id:integer content:text rake db:migrate 

Then I added the associations to the models like so

class Question < ActiveRecord::Base   belongs_to :survey end 

and so

class Survey < ActiveRecord::Base   has_many :questions   accepts_nested_attributes_for :questions end 

Then I added the nested view part

<%= form_for(@survey) do |f| %>   <!-- Standard rails 4 view stuff -->    <div class="field">     <%= f.label :name %><br>     <%= f.text_field :name %>   </div>   <div class="field">     <%= f.fields_for :questions do |builder| %>       <div>         <%= builder.label :content, "Question" %><br/>         <%= builder.text_area :content, :rows => 3 %>       </div>     <% end %>   </div>   <div class="actions">     <%= f.submit %>   </div> <% end %> 

and finally the controller so that 3 questions are created whenever a new survey is instantiated

class SurveysController < ApplicationController   before_action :set_survey, only: [:show, :edit, :update, :destroy]    # Standard rails 4 index and show     # GET /surveys/new   def new     @survey = Survey.new     3.times { @survey.questions.build }     Rails.logger.debug("New method executed")   end    # GET /surveys/1/edit   def edit   end    # Standard rails 4 create    # PATCH/PUT /surveys/1   # PATCH/PUT /surveys/1.json   def update     respond_to do |format|       if @survey.update(survey_params)         format.html { redirect_to @survey, notice: 'Survey was successfully updated.' }         format.json { head :no_content }       else         format.html { render action: 'edit' }         format.json { render json: @survey.errors, status: :unprocessable_entity }       end     end   end    # Standard rails 4 destroy    private     # Use callbacks to share common setup or constraints between actions.     def set_survey       @survey = Survey.find(params[:id])     end      # Never trust parameters from the scary internet, only allow the white list through.     def survey_params       params.require(:survey).permit(:name, questions_attributes: [:content])     end end 

So, creating a new survey with three questions is fine. However, if I try to edit one of the surveys, the original three questions are maintained, while an additional three more are created. So instead of having 3 questions for the edited survey, I now have 6. I added

Rails.logger.debug("New method executed") 

to the new method in the controller, and as far as I can tell, it is not executed when I'm doing an edit operation. Can anyone tell me what I'm doing wrong?

Any help is greatly appreciated!

Answer 1

So I figured it out. I had to add :id to the permitted params in the survey_params method. It now looks like this:

# Never trust parameters from the scary internet, only allow the white list through. def survey_params   params.require(:survey).permit(:name, questions_attributes: [:id, :content]) end 

which works perfectly. I'm a RoR newbie, so please take my analysis of this with a grain of salt, but I guess that new id's where generated instead of being passed to the update action. Hope this helps someone else out there.