I am new to rails and am trying to build a blog app where only signed in users can see the username of the person who created a post, however I keep getting this error NoMethodError in Posts#index undefined method `username' for nil:NilClass

screenshot of error in localhost:3000

Here is my routes.rb

```
Rails.application.routes.draw do


  devise_for :users
  # Define your application routes per the DSL in         https://guides.rubyonrails.org/routing.html

  # Defines the root path route ("/")
  # root "articles#index"

  root "posts#index"


resources :posts, only: [:new, :create, :index]

get "/posts/new.html.erb", to: "posts#create", as: "create"
get "/posts/new.html.erb", to: "posts#new", as: "new"
end

```

here is my posts_controller.rb

    class PostsController < ApplicationController

    before_action :authenticate_user!, except: [:index]

    def new
        @post = Post.new
    end

    def create 
        
        @post = current_user.posts.build(post_params)
        @post.user = current_user

        respond_to do |format|
        if @post.save
            
            format.html { redirect_to user_post_path(current_user, @post), notice: 'Post was successfully created.' }
            format.json { render :show, status: :created, location: @post }
            
          else
            
            format.html { render :new }
            format.json { render json: @post.errors, status: :unprocessable_entity }
            end
          end
    end

    def index 
        @posts = Post.all.order(created_at: :desc)
        
    end

    private

    def post_params
        params.require(:post).permit(:title, :description)
    end
    

    end
    ```


here is my post.rb model


    ```
    class Post < ApplicationRecord
    belongs_to :user
    end
    ```

here is my user.rb model


    ```
    class User < ApplicationRecord
      # Include default devise modules. Others available are:
      # :confirmable, :lockable, :timeoutable, :trackable and :omniauthable
      devise :database_authenticatable, :registerable,
             :recoverable, :rememberable, :validatable

   
         
      has_many :posts


      validates :username, presence: true
      validates :email, presence: true
      validates :password, presence: true

    end




  
    ``



here is my schema




    ```
    ActiveRecord::Schema[7.0].define(version: 2022_11_14_173843) do
      create_table "posts", force: :cascade do |t|
    t.string "title"
    t.text "description"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.integer "user_id"
   end

    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.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.string "username"
    t.index ["email"], name: "index_users_on_email", unique: true
    t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
  end

    end
 
    ```
here is my AddNameToUsers migration


    ```
    class AddNameToUsers < ActiveRecord::Migration[7.0]
      def change
    add_column :users, :username, :string
    end
    end

    ```

Here is my AddUserIdToPosts migration

    
    ```
    class AddUserIdToPosts < ActiveRecord::Migration[7.0]
   def change
    add_column :posts, :user_id, :integer
    
    end
     end
    ```


Here is my CreatePosts Migration



     ```
    class CreatePosts < ActiveRecord::Migration[7.0]
    def change
    create_table :posts do |t|
      t.string :title
      t.text :description
      
      t.timestamps
    end
    end
    end

    ```

CodePudding user response：

Try debugging the post object which is raising the Exception.

It looks like there is a Post object which doesnt have a user associated with it. So post.user returns nil and when username method is called on the nil object an Exception is raised as it is not defined on nil.

You may check in the rails console which post doesnt have a user associated with it and based on your requirements either correct such objects or remove the objects from being displayed in index or just do not show a username for posts if it is not present.

CodePudding user response：

I finally got it working, for the link_to error, I simply needed to remove the only: function in my routes.rb to only say resources :posts and for the username error I referenced a user in my createPosts migration and then cleared the Posts and Users in the rails console and started over from signing up to making a post to viewing all posts to seeing a single post