undefined method `find' for BooksTag:Classエラー

編集画面に飛ぶ際にエラーがおきます

フォームオブジェクトにてtagsとbooksを結びつけてからこのようなエラーが起きました

bookコントローラー
部分でエラー

class BooksController < ApplicationController
  before_action :search_book, only: [:index, :search]

  def new
    @book = BooksTag.new
  end

  def index
   @books =Book.all.order(created_at: :desc)
   set_book_column 
  end

  def show
    @book = Book.find(params[:id])
  end

  def destroy
    book = BooksTag.find(params[:id])
    book.destroy
    redirect_to  books_path 
  end

  def create
    # @book = Book.new(book_params)
   
    @book = BooksTag.new(book_params)
    if @book.valid?
      @book.save
      redirect_to root_path
    else
      render 'new'
    end
  end
  def search
    @results = @p.result 
    @books =Book.all.order(created_at: :desc)
  end
  def edit
    @book = BooksTag.find(params[:id])
  end

  def update
    book = BooksTag.find(params[:id])
    book.update(book_params)
    redirect_to root_path
  end

  private

  def book_params
    params.require(:books_tag).permit(:name, :content,:genre_id,:image,:tag_name).merge(user_id: current_user.id)
  end


  def search_book
    @books =Book.all
    @p = Book.ransack(params[:q]) 
  end
  def set_book_column
    @book_name = Book.select("genre_id").distinct  # 重複なくnameカラムのデータを取り出す
   end
end

　　tagとbookをまとめているformオブジェクト

class BooksTag

  include ActiveModel::Model
  attr_accessor :content, :name,:genre_id,:image,:user_id,:tag_name
 
  with_options presence: true do
    validates :content
    validates :name
    validates :genre_id
    validates :tag_name
    validates :image
  end
 
  def save
    book = Book.create(content: content,name: name,genre_id: genre_id,image: image,user_id: user_id)

    tag = Tag.create(tag_name: tag_name)
    tag = Tag.where(tag_name: tag_name).first_or_initialize
    tag.save

    tag_relation =TagRelation.create(book_id: book.id, tag_id: tag.id)
    tag_relation.save

  end
 
 end

モデル関係

book.rb
  has_many :tag_relations
  has_many :tags, through: :tag_relations



tag.rb
class Tag < ApplicationRecord
 has_many :tag_relations
 has_many :books, through: :tag_relations
end


tag.relation.rb
class TagRelation < ApplicationRecord
  belongs_to :book
  belongs_to :tag
end

book edit.html.erb

<body><div class="container">
<div class="sec1title">
    <h2>＊画像を投稿！＊</h2>
  </div>
  
<%= form_for (@book)  do |f| %>

  <div class="field" type="text">
    <%= f.label :name, "本の名前" %><br />
    <%= f.text_field :name %>
  </div>
  <div class="tag-field", id='tag-field'>
     <%= f.label :tag_name, "タグ" %>
     <%= f.text_field :tag_name, placeholder: "検索されやすいキーワードを入れましょう" %>
   </div>
   <div class="genre" >
    <%= f.label :genre_id, "本のジャンル" %><br />
    <%= f.collection_select(:genre_id,Genre.all,:id,:type,{prompt: "---"},{class:"select-box"}) %>
  </div>
  <div class="form-input">
   <div class="text-image-content">
     <%= f.label :content, "説明文" %><br />
  <%= f.text_area :content, placeholder: "話したい内容について、ご自由にお書きください" , rows: "12" %> 
  </div>
  <br /><br /> 
    <label class="form-image">
      <span class="image-file">画像</span>
      <%= f.file_field :image %>
    </label>
    <div class="image-stage", id="image-list"></div>
  </div>

  <div class="actions">
    <%= f.submit "更新", class: "btn1" %>
  </div>
<% end %>
</div>
</body>

findをallにしてりcreateしてみたが違うエラーが出ます
https://gyazo.com/5ea5d098c2275b2377d9755baf901af7