NoMethod错误-为什么会出现此错误？

Question

This is my Genre controller code:

class GenresController < ApplicationController
  before_action :set_genre, only: [:show, :edit, :update, :destroy]
  before_action :authenticate_user!, except: [:index, :show]




    def index
        @genres = Genre.all.order("created_at desc")
      end


      def show
      end

      def new
        @genre = current_user.genres.build
      end

      def edit
      end


      def create
        @genre = current_user.genres.build(genre_params)

        respond_to do |format|
          if @genre.save
            format.html { redirect_to @genre, notice: 'Genre was successfully created.' }
            format.json { render :show, status: :created, location: @genre }
          else
            format.html { render :new }
            format.json { render json: @genre.errors, status: :unprocessable_entity }
          end
        end
      end

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


  def destroy
    @genre.destroy
    respond_to do |format|
      format.html { redirect_to genres_url, notice: 'Genre was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private

      @genre = Genre.find(params[:id])
    end


    def genre_params
      params.require(:genre).permit(:artist, :album, :songs, :price)
    end
end

And this is my form code :

<%= simple_form_for @genre, html: { multipart: true } do |f| %>
  <%= f.error_notification %>

    <div class="columns">

      <div class="field column is-9">
        <div class="control">
          <%= f.input :genres, required: true, input_html: { class: "input"}, wrapper: false, label_html: { class:"label" } %>
        </div>
      </div>

      <div class="field column">
        <div class="control">
          <%= f.input :artist, required: true, input_html: { class:"input", maxlength: 7  }, wrapper: false, label_html: { class:"label" } %>
        </div>
      </div>

    </div>

    <div class="field">
      <div class="control">
        <%= f.input :songs, required: true, input_html: { class:"input" }, wrapper: false, label_html: { class:"label" } %>
      </div>
    </div>

    <div class="field">
      <div class="control">
        <%= f.input :description, required: true, input_html: { class:"textarea" }, wrapper: false, label_html: { class:"label" } %>
      </div>
    </div>

    <div class="field">
      <div class="control">
        <label class="label">Add images</label>
          <div class="file">
          <label class="file-label">
            <%= f.input :image, as: :file, input_html: { class:"file-input instrument-image" }, label: false, wrapper: false %>
              <span class="file-cta">
                <span class="file-icon"><i class="fa fa-upload"></i></span>
                <span class="file-label">Choose a file…</span>
              </span>
          </label>
          </div>
        </div>
      </div>
      <output id="list"></output>
    <hr />

     <div class="field column">
        <div class="control">
          <%= f.input :price, required: true, input_html: { class:"input", maxlength: 7  }, wrapper: false, label_html: { class:"label" } %>
        </div>
      </div>

    <div class="field is-grouped">
      <div class="control">
        <%= f.button :submit, class: 'button is-warning' %>
        <%= link_to 'Cancel', genres_path, class:'button is-light' %>
      </div>
    </div>

  <% end %>

Answer 1

You are using form_for which directly maps html form to object @genre , so rails expects either below one condition to be met

1. genres column in genres table
2. genres attr_accessor in Genre.rb model.
3. instance method by name genres in Genre.rb model.

In your case all three missing.

This line causing the issue

<%= f.input :genres, required: true, input_html: { class: "input"}, wrapper: false, label_html: { class:"label" } %>

I hope it clarifies your issue to some level. Better you provide more details on what you are trying to achieve, it helps everyone to answer in better way.

One thing for sure there is no logic in having genres input field in genre form.