rails 4未定義のメソッド 'name' for nil：NilClass - カテゴリ

Question

カテゴリ名に従って画像を表示したい。私の画像は、app/assets/images にあります。私の作品は、私がコンソールに作成したカテゴリを持っています。 今、このエラーがあります（もう一度...）​​。 貴重なご支援をいただき、ありがとうございます。ここ

は私のフォームです：

= simple_form_for @tuto do |f| 
    - if @tuto.errors.any? 
    #error_explanation 
     h2 = "#{pluralize(@tuto.errors.count, "error")} prohibited this tuto from being saved:" 
     ul 
     - @tuto.errors.full_messages.each do |message| 
      li = message 
    = f.hidden_field :user_id, value: current_user.id 
    = f.input :title 
    = f.collection_select :category_id, Category.all, :id, :name, {prompt: "Choose a category"} 
    = f.input :content, as: :text, input_html: { rows: "15" } 
    = f.button :submit, "Save" 

tutos_controller.rb

class TutosController < ApplicationController 
    before_action :authenticate_user! 
    before_action :set_tuto, only: [:show, :edit, :update, :destroy, :upvote] 


    def index 
    @tutos = Tuto.all.includes(:user, :category) 
    end 

    def show 
    @tuto = Tuto.find(params[:id]) 
    @user = User.all 
    end 


    def new 
    @tuto = Tuto.new 
    end 

    def edit 
    end 

    def create 

    @tuto = Tuto.new(tuto_params) 
    @tuto.user_id = current_user.id 

    respond_to do |format| 
     if @tuto.save 
     flash[:success] = "Test" 
     format.html { redirect_to @tuto, notice: 'Tuto was successfully created.' } 
     format.json { render :show, status: :created, location: @tuto } 
     else 
     format.html { render :new } 
     format.json { render json: @tuto.errors, status: :unprocessable_entity } 
     end 
    end 
    end 


    def update 
    respond_to do |format| 
     if @tuto.update(tuto_params) 
     format.html { redirect_to @tuto, notice: 'Tuto was successfully updated.' } 
     format.json { render :show, status: :ok, location: @tuto } 
     else 
     format.html { render :edit } 
     format.json { render json: @tuto.errors, status: :unprocessable_entity } 
     end 
    end 
    end 


    def destroy 
    @tuto.destroy 
    respond_to do |format| 
     format.html { redirect_to tutos_url, notice: 'Tuto was successfully destroyed.' } 
     format.json { head :no_content } 
    end 
    end 


    def upvote 
    @tuto.upvote_by current_user 
    redirect_to :back 
    end 

    private 
    # def get_user 
    # @user = User.find(@tuto.user_id) 
    # end 

    def set_tuto 
     @tuto = Tuto.find(params[:id]) 
    end 

    def tuto_params 
     params.require(:tuto).permit(:title, :content, :id, :user_id, :category_id) 
    end 
end 

categories_controller.rb

class CategoriesController < ApplicationController 

    private 

    def categories_params 
     params.require(:categories).permit(:name, :description, :id) 
    end 

end 

私の見解/ TUTOS/index.html.slim

.container 
    .row 
    .col-xs-12.col-sm-12 
     h1.text-gray Tutorials 
     br 
     -if user_signed_in? 
     = link_to "Create a tuto", new_tuto_path, class:"btn btn-success" 

    #tutos.transitions-enabled 
    - @tutos.each do |tuto| 
     .box.panel-default 
     -if tuto.category.name == "Ruby" 
      =image_tag("select/ruby.png") 
     -elsif tuto.category.name == "Rails 4" 
      =image_tag("selec/rails4.png") 
     -elsif tuto.category.name == "Rails 5" 
      =image_tag("selec/rails5.png") 
     -elsif tuto.category.name == "Heroku" 
      =image_tag("select/heroku.png") 
     -elsif tuto.category.name == "AWS" 
      =image_tag("select/aws.png") 



     = link_to tuto.title, tuto_path(tuto)  
     h6 Created by: 
     = tuto.user.full_name 
    hr 

ここで私のschema.rb

ActiveRecord::Schema.define(version: 20160920133801) do 

    create_table "categories", force: :cascade do |t| 
    t.string "name" 
    t.text  "description" 
    t.string "image" 
    t.datetime "created_at", null: false 
    t.datetime "updated_at", null: false 
    end 

    create_table "tutos", force: :cascade do |t| 
    t.datetime "created_at", null: false 
    t.datetime "updated_at", null: false 
    t.string "title" 
    t.text  "content" 
    t.integer "user_id" 
    t.integer "category_id" 
    end 

    add_index "tutos", ["user_id"], name: "index_tutos_on_user_id" 

    create_table "users", force: :cascade do |t| 
    t.string "email",     default: "", null: false 
    t.string "encrypted_password",  default: "", null: false 
    t.string "reset_password_token" 
    t.datetime "reset_password_sent_at" 
    t.datetime "remember_created_at" 
    t.integer "sign_in_count",   default: 0, null: false 
    t.datetime "current_sign_in_at" 
    t.datetime "last_sign_in_at" 
    t.string "current_sign_in_ip" 
    t.string "last_sign_in_ip" 
    t.datetime "created_at",       null: false 
    t.datetime "updated_at",       null: false 
    t.string "first_name" 
    t.string "last_name" 
    t.boolean "admin" 
    end 

    add_index "users", ["email"], name: "index_users_on_email", unique: true 
    add_index "users", ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true 

    create_table "votes", force: :cascade do |t| 
    t.integer "votable_id" 
    t.string "votable_type" 
    t.integer "voter_id" 
    t.string "voter_type" 
    t.boolean "vote_flag" 
    t.string "vote_scope" 
    t.integer "vote_weight" 
    t.datetime "created_at" 
    t.datetime "updated_at" 
    end 

    add_index "votes", ["votable_id", "votable_type", "vote_scope"], name: "index_votes_on_votable_id_and_votable_type_and_vote_scope" 
    add_index "votes", ["voter_id", "voter_type", "vote_scope"], name: "index_votes_on_voter_id_and_voter_type_and_vote_scope" 

end 

EDITはエラーメッセージです：あなたはいくつかの点でCATEGORY_IDことなく、少なくとも1つのTutoオブジェクトを作成している可能性があり、それはあなたの（まだだよう

Answer 1

が見えます開発？）データベース。私はあなたがそれを望んでいないと思っています。その場合、私は通常開発データベースをrake db:resetで拭き取ります。もちろん、それを行う場合は、開発中のコマンドを実行していることを確認してください。将来的には、Tutoモデルのcategory_idの存在を検証することもできます。