Can't mass-assign protected attributes:: issue while building a nested attribute form

Question

I've spent nearly all day on this particular issue and although there are other posts about it, I've not resolved my particular issue.

I've tried following RailsCast #196 but still can't identify my mistake.

MODELS:

Exercises

# == Schema Information
#
# Table name: exercises
#
#  id          :integer          not null, primary key
#  name        :string(255)
#  description :text
#  created_at  :datetime         not null
#  updated_at  :datetime         not null
#  image       :string(255)
#

class Exercise < ActiveRecord::Base
  attr_accessible :description, :name, :tags_attributes
  has_many :tags
  has_one :difficulty
  accepts_nested_attributes_for :tags, :allow_destroy => true
end

Tags

# == Schema Information
#
# Table name: tags
#
#  id         :integer          not null, primary key
#  name       :string(255)
#  created_at :datetime         not null
#  updated_at :datetime         not null
#

class Tag < ActiveRecord::Base
  attr_accessible :name, :exercise_id
  belongs_to :exercise
  accepts_nested_attributes_for :exercises
end

FORM

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

      <ul>
      <% @exercise.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>
  <div class="field">
    <%= f.label :description %><br />
    <%= f.text_area :description %>
  </div>
  <%= f.fields_for :tag do |builder| %>
    <div class="field">
        <%= builder.label :name, "Tags" %><br />
        <%= builder.text_field :name %>     
    </div>
<% end %>
  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>

The error, specifically, when I submit the form is:

ActiveModel::MassAssignmentSecurity::Error in ExercisesController#create

Can't mass-assign protected attributes: tag

Application Trace | Framework Trace | Full Trace
app/controllers/exercises_controller.rb:42:in `new'
app/controllers/exercises_controller.rb:42:in `create'

Luís Ramalho Luís Ramalho · Accepted Answer · 2013-04-06T02:37:04

In your form, replace the line

<%= f.fields_for :tag do |builder| %>

with

<%= f.fields_for :tags do |builder| %>

In your model you're using attr_accessible and then you add the plural followed by _attributes so you can set the attributes, but in your form you called the singular tag hence why you're getting a mass-assign protected attributes error.

Can't mass-assign protected attributes:: issue while building a nested attribute form

1 Answers