Question

I have set up a HABTM relationship between two table creating a many to many relationship between items and categories. I want to add an item connected with one or more categories via the add item form. when I submit the form I am getting the error “Can’t mass-assign protected attributes: categories”.

Here are my models:

class Item < ActiveRecord::Base
  attr_accessible :description, :image, :name

  has_attached_file :image, :styles => { :medium => "300x300>", :thumb => "100x100>" }

  belongs_to :user
  has_and_belongs_to_many :categories

  validates :name, presence: true, length: {maximum: 50}
  accepts_nested_attributes_for :categories
end

class Category < ActiveRecord::Base
  attr_accessible :description, :name
  has_and_belongs_to_many :items

  validates :name, presence: true, length: {maximum: 50}
end

And my migrations:

class CreateItems < ActiveRecord::Migration
  def change
    create_table :items do |t|
      t.string :name
      t.text :description
      t.has_attached_file :image

      t.timestamps
    end
  end
end

class CreateCategories < ActiveRecord::Migration
  def change
    create_table :categories do |t|
      t.string :name
      t.string :description

      t.timestamps
    end
  end
end

class CreateCategoriesItems < ActiveRecord::Migration
  def up
    create_table :categories_items, :id => false do |t|
      t.integer :category_id
      t.integer :item_id
    end
  end

  def down
    drop_table :categories_items
  end
end

And my form looks like this:

<%= form_for(@item, :html => { :multipart => true }) do |f| %>
  <%= render 'shared/error_messages', object: f.object %>


  <%= f.label :name %>
  <%= f.text_field :name %>

  <%= f.label :description %>
  <%= f.text_field :description %>
  <%= f.file_field :image %>
  <%= f.collection_select(:categories, @categories,:id,:name)%>
  <%= f.submit "Add Item", :class => "btn btn-large btn-primary" %>
<% end %>

and here’s my Items Controller:

class ItemsController < ApplicationController

  def new
    @item = Item.new
    @categories = Category.all
  end

  def create
    @item = Item.new(params[:item])
    if @item.save
      #sign_in @user
      flash[:success] = "You've created an item!"
      redirect_to root_path
    else
      render 'new'
    end
  end

  def show
  end

  def index
    @items = Item.paginate(page: params[:page], per_page: 3)
  end


end

Thanks for all of your help 🙂

-Rebekah

Answer 1

IAmNaN posted the comment above that was the missing link in my code working properly. I have since written a blog post that details the process of getting the HABTM set-up. Thanks IAmNaN!