Question

尝试在基本的has_many和belongs_to关联中学习accepts_nested_attributes_for。

问题是它在展示页面中无效...

我得到的错误是：

NoMethodError in Authors#show   

undefined method `each' for nil:NilClass

与此行有关：<%= @book.each do |b| %>

基本设置是：

作者

class Author < ApplicationRecord
    has_many :books

    accepts_nested_attributes_for :books
end

预订

class Book < ApplicationRecord
    belongs_to :author
end

作者_form.html.erb

<%= form_with(model: author, local: true) do |form| %>
  <% if author.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(author.errors.count, "error") %> prohibited this author from being saved:</h2>

      <ul>
      <% author.errors.full_messages.each do |message| %>
        <li><%= message %></li>
      <% end %>
      </ul>
    </div>
  <% end %>

  <div class="field">
    <%= form.label :name %>
    <%= form.text_field :name, id: :author_name %>
  </div>

  <h3>Book </h3>
  <%= form.fields_for :books do |b| %>
    <div class="field">
      <%= b.label :title %><br />
      <%= b.text_field :title %>
    </div>
  <% end %>

  <div class="actions">
    <%= form.submit %>
  </div>
<% end %>

作者控制器

class AuthorsController < ApplicationController
  before_action :set_author, only: [:show, :edit, :update, :destroy]

  # GET /authors
  # GET /authors.json
  def index
    @authors = Author.all
  end

  # GET /authors/1
  # GET /authors/1.json
  def show
  end

  # GET /authors/new
  def new
    @author = Author.new
    @book = @author.books.build
  end

  # GET /authors/1/edit
  def edit
  end

  # POST /authors
  # POST /authors.json
  def create
    @author = Author.new(author_params)

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

  # PATCH/PUT /authors/1
  # PATCH/PUT /authors/1.json
  def update
    respond_to do |format|
      if @author.update(author_params)
        format.html { redirect_to @author, notice: 'Author was successfully updated.' }
        format.json { render :show, status: :ok, location: @author }
      else
        format.html { render :edit }
        format.json { render json: @author.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /authors/1
  # DELETE /authors/1.json
  def destroy
    @author.destroy
    respond_to do |format|
      format.html { redirect_to authors_url, notice: 'Author was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_author
      @author = Author.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def author_params
      params.require(:author).permit(:name, books_attributes: [:id, :title])
    end
end

作者的show.html.erb

<p id="notice"><%= notice %></p>

<p>
  <strong>Name:</strong>
  <%= @author.name %>
</p>

<p>
    <strong>Book(s)</strong>
    <%= @book.each do |b| %>
        <%= "#{b.name}" %><br />
    <% end %>
</p>

<%= link_to 'Edit', edit_author_path(@author) %> |
<%= link_to 'Back', authors_path %>

Answer 1

在显示操作中放置此

def show
 @books = @author.books
end

<强> show.html.erb

<strong>Book(s)</strong>
<%= @books.each do |b| %>
    <%= b.title %><br />
<% end %>

在新操作中删除该行

@book = @author.books.build

显示页面不适用于Accepts_Nested_Attributes_For

1 个答案: