Rails Friendly Id - Couldn't find Category with id=electronics

I'm trying to develop a app in Ruby on Rails 4.0 (already used older versions of this incredible framework) and I having some troubles. I installed the FriendlyID gem and I think everything is okay, but I'm receiving errors when I try to test my app. If I go to `http://0.0.0.0:3000/categories/1`, this works. But when I click in "edit" in this page, or just go to `http://0.0.0.0:3000/categories/electronics` (that's the slugged name of category with ID 1), I receive the following error: ``` Couldn't find Category with id=electronics # Use callbacks to share common setup or constraints between actions. def set_category @category = Category.find(params[:id]) #Here's pointed the error end ``` Category Model: ``` class Category < ActiveRecord::Base extend FriendlyId friendly_id :name, use: :slugged # Validations validates_uniqueness_of :name, :case_sensitive => false end ``` Category Controller: (generated by scaffold for test purposes) ``` class CategoriesController < ApplicationController before_action :set_category, only: [:show, :edit, :update, :destroy] # GET /categories # GET /categories.json def index @categories = Category.all end # GET /categories/1 # GET /categories/1.json def show end # GET /categories/new def new @category = Category.new end # GET /categories/1/edit def edit end # POST /categories # POST /categories.json def create @category = Category.new(category_params) respond_to do |format| if @category.save format.html { redirect_to @category, notice: 'Category was successfully created.' } format.json { render action: 'show', status: :created, location: @category } else format.html { render action: 'new' } format.json { render json: @category.errors, status: :unprocessable_entity } end end end # PATCH/PUT /categories/1 # PATCH/PUT /categories/1.json def update respond_to do |format| if @category.update(category_params) format.html { redirect_to @category, notice: 'Category was successfully updated.' } format.json { head :no_content } else format.html { render action: 'edit' } format.json { render json: @category.errors, status: :unprocessable_entity } end end end # DELETE /categories/1 # DELETE /categories/1.json def destroy @category.destroy respond_to do |format| format.html { redirect_to categories_url } format.json { head :no_content } end end private # Use callbacks to share common setup or constraints between actions. def set_category @category = Category.find(params[:id]) end # Never trust parameters from the scary internet, only allow the white list through. def category_params params.require(:category).permit(:name) end end ``` Migration:## (I added friendlyId after create the Category table, but I think is okay) ``` class AddColumnToCategory < ActiveRecord::Migration def change add_column :categories, :slug, :string add_index :categories, :slug, unique: true end end ``` Routes: ``` resources :categories ``` Hope you can help me. What I'm doing wrong in Rails 4.0?