投稿一覧ページにユーザ情報を表示させたい

Question

##前提・実現したいこと
railsでSNSのようなサイトを作成しておりますが、
投稿一覧画面でユーザー名等を表示したいのですがエラーが発生してしまいます。

rails g migration AddUserIdToPostsでpostsとuserを紐付ける用にマイグレーションファイルをを作成しました。

class AddUserIdToPosts < ActiveRecord::Migration[6.1]
  def change
    add_reference :posts, :user, foreign_key: true
  end
end

##エラー内容

NoMethodError in Posts#index
Showing /app/app/views/posts/index.html.erb where line #10 raised:

undefined method `name' for nil:NilClass
Extracted source (around line #10):
              
<div class="name-history">
 <div class="name">テキスト 太郎
  <%= post.user.name %>
 </div>
 <div class="learning-history">学習歴: 2月</div>
</div>

##posts_controller.rb

class PostsController < ApplicationController
  before_action :authenticate_user!
  before_action :find_post, only: [:show, :edit, :update, :destory]
  before_action :force_redirect_unless_my_post, only: [:edit, :update, :destory]

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

  def show
  end

  def new
    @post = Post.new
  end

  def edit
  end

  def create
    @post = Post.new(post_params)
    @post.user = current_user
    if @post.save!
      redirect_to root_path, notice: '投稿成功!!'
    else
      render :new
    end
  end

  def update
    if @post.update(post_params)
      redirect_to root_path, notice: '投稿を更新しました。'
    else
      render :edit
    end
  end

  def destory
    if @post.destory
      redirect_to root_path, notice: '投稿を削除しました。'
    else
      redirect_to root_path, alert: '投稿が削除できませんでした。'
    end
  end

  private

  def post_params
    params.require(:post).permit(
      :thumbnail,
      :title,
      :version,
      :code,
      :description,
      :video,
      images: [],
    )
  end

  def find_post
    @post = Post.find_by(params[:id])
  end

  def force_redirect_unless_my_post
    return redirect_to root_path, alert: '自分の投稿ではありません' if @post.user != current_user
  end
end

##models/post.rb

class Post < ApplicationRecord
  has_many_attached :images
  has_one_attached :video
  belongs_to :user
end

##models/user.rb

class User < ApplicationRecord
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :validatable

  has_one_attached :image
  has_many :posts, dependent: :destroy

  validates :name, presence: true
end

##schema.rb

# This file is auto-generated from the current state of the database. Instead
# of editing this file, please use the migrations feature of Active Record to
# incrementally modify your database, and then regenerate this schema definition.
#
# This file is the source Rails uses to define your schema when running `bin/rails
# db:schema:load`. When creating a new database, `bin/rails db:schema:load` tends to
# be faster and is potentially less error prone than running all of your
# migrations from scratch. Old migrations may fail to apply correctly if those
# migrations use external dependencies or application code.
#
# It's strongly recommended that you check this file into your version control system.

ActiveRecord::Schema.define(version: 2021_02_21_020851) do

  create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
    t.string "name", null: false
    t.string "record_type", null: false
    t.bigint "record_id", null: false
    t.bigint "blob_id", null: false
    t.datetime "created_at", null: false
    t.index ["blob_id"], name: "index_active_storage_attachments_on_blob_id"
    t.index ["record_type", "record_id", "name", "blob_id"], name: "index_active_storage_attachments_uniqueness", unique: true
  end

  create_table "active_storage_blobs", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
    t.string "key", null: false
    t.string "filename", null: false
    t.string "content_type"
    t.text "metadata"
    t.string "service_name", null: false
    t.bigint "byte_size", null: false
    t.string "checksum", null: false
    t.datetime "created_at", null: false
    t.index ["key"], name: "index_active_storage_blobs_on_key", unique: true
  end

  create_table "active_storage_variant_records", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
    t.bigint "blob_id", null: false
    t.string "variation_digest", null: false
    t.index ["blob_id", "variation_digest"], name: "index_active_storage_variant_records_uniqueness", unique: true
  end

  create_table "posts", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
    t.string "thumbnail"
    t.string "title"
    t.integer "version"
    t.integer "code"
    t.text "description"
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
    t.bigint "user_id"
    t.index ["user_id"], name: "index_posts_on_user_id"
  end

  create_table "users", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", 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", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
    t.string "name", default: "", null: false
    t.text "description"
    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

  add_foreign_key "active_storage_attachments", "active_storage_blobs", column: "blob_id"
  add_foreign_key "active_storage_variant_records", "active_storage_blobs", column: "blob_id"
  add_foreign_key "posts", "users"
end

##views/posts/index.html.erb

<div class="wrapper">
  <div class="content-block">
    <% @posts.each do |post| %>
      <div class="content">
        <div class="user-about">
          <div class="image"><%= image_tag 'img1.png' %></div>
          <div class="profile">
            <div class="name-history">
              <div class="name">テキスト 太郎
                <%= post.user.name %>
              </div>
              <div class="learning-history">学習歴: 2月</div>
            </div>
            <div class="purpose">Railsを勉強している目的: webエンジニアを目指してRailsを学んで転職活動中!!!</div>
          </div>
        </div>

        <% if post.images.attached? %>  
          <div class="images">
            <% post.images.each do |image| %>
              <%= image_tag image %>
            <% end %>
          </div>
        <% end %>

        <% if post.video.attached? %>  
          <div class="video">
              <%= video_tag(url_for(post.video), style: 'width:100%;height:auto', controls: true, loop: true, autoplay: true, muted: true) %>
          </div>
        <% end %>


        <div class="text">
          <%= post.description %>
          <%= post.thumbnail %>
          <%= post.title %>
          <%= post.version %>
          <%= post.code %>
        </div>
        <div class="action-menu">
          <div class="like">

          </div>
          <div class="comment">

          </div>
        </div>
      </div>
    <% end %>
  </div>
  <div class="sidebar">
    <div class="box"></div>
    <div class="box"></div>
  </div>
</div>

Answer 1

postsとuserを紐付けた際は、一度postsのデータをすべて削除することで解決しました。