Invalid association. Make sure that accepts_nested_attributes_for is used for :questions association

Question

i am building nested form in rails 4.I keep getting this error

my _form.html.erb as

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

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

    <div class="field">
    <%= f.label :name %><br>
    <%= f.text_field :name %>
    </div>

    <%= f.fields_for :questions do |builder| %>
    <%= render "question_fields", :f => builder %>
    <% end %>

    <div class="actions">
    <%= f.submit %>
    </div>
    <% end %>

_question.html.erb

      <p>
            <%= f.label :content, "Question" %><br />
            <%= f.text_area :content, :rows => 3 %><br />
            <%= f.label :subject, "Question" %><br />
            <%= f.text_field :subject %><br />
            <%= f.link_to_remove "Remove this task" %>
            <p><%= f.link_to_add "Add a questions",:questions %></p>
     </p>

project.rb

       has_many :questions, :dependent => :destroy

       accepts_nested_attributes_for :questions, :reject_if => lambda { |a| a[:content].blank? }, :allow_destroy => true

Edit

question.rb

      class Question < ActiveRecord::Base

       belongs_to :project

       end

projects controller

      def new
      @project = Project.new
       3.times do
       question = @project.questions.build
        end
      def project_params
      params.require(:project).permit(:name)
      end

        def create
        @project = Project.new(project_params)

        respond_to do |format|
        if @project.save
        format.html { redirect_to @project, notice: 'Project was successfully created.' }
         format.json { render :show, status: :created, location: @project }
        else
         format.html { render :new }
        format.json { render json: @project.errors, status: :unprocessable_entity }
       end
      end

end

I used "nested_form" gem Gives Error Invalid association. Make sure that accepts_nested_attributes_for is used for :questions association.

pls help me to get rid of this error

questions controller def:-

      def question_params
      params.require(:question).permit(:project_id, :subject, :content)
      end

Answer 1

Might be your problem is with your strong parameters

Try changing your project_params in your projects_controller as

def project_params
  params.require(:project).permit(:name,questions_attributes: [:project_id,:subject,:content])
end

And also,your controller code should look like this

def new
  @project = Project.new
  3.times do
    @question = @project.questions.build
  end
end

def create
  @project = Project.new(project_params)

  respond_to do |format|
    if @project.save
      format.html { redirect_to @project, notice: 'Project was successfully created.' }
      format.json { render :show, status: :created, location: @project }
    else
      format.html { render :new }
      format.json { render json: @project.errors, status: :unprocessable_entity }
    end
  end
end

private

def project_params
  params.require(:project).permit(:name,questions_attributes: [:project_id,:subject,:content])       
end

Also,you have to look for Strong Parameters with accepts_nested_attributes_for.

Update

Try changing your _form.html.erb as

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

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

  <div class="field">
    <%= f.label :name %><br>
    <%= f.text_field :name %>
  </div>

  <%= f.fields_for :questions do |builder| %>
    <%= render "question_fields", :ff => builder %> #changed to ff to avoid confusion
    <% end %>
    <p><%= f.link_to_add "Add a questions",:questions %></p> #this line it should be here.
    <div class="actions">
    <%= f.submit %>
    </div>
  <% end %>

And your _question_fields.html.erb as

<p>
  <%= ff.label :content, "Question" %><br />
  <%= ff.text_area :content, :rows => 3 %><br />
  <%= ff.label :subject, "Question" %><br />
  <%= ff.text_field :subject %><br />
  <%= ff.link_to_remove "Remove this task" %>       
</p>