Question

我收到一条错误消息，指出我的show.html.erb页面中未定义的方法'name'。如果它说@ book.category.name，它会一直说未定义的方法名称。

show.html.erb

mix phoenix.server

Books_Controller.rb

while(move <= 0 || move >= 10 )
{
   System.out.println("that move is invalid must be 1-9");
   System.out.print("Where do you want to move? ");
   move = in.nextInt();
}

Book.rb

    <h1><%= @book.title %></h1>
<h3><%= @book.author %></h3>
<h4>Category: <%= @book.category.name %></h4>
<p><%= @book.description %></p>

<%= link_to "Back", root_path %>


<% if user_signed_in? %>
<% if @book.user_id == current_user.id %>

<%= link_to "edit", edit_book_path(@book) %>
<%= link_to "Delete", book_path(@book), method: :delete, data: {confirm: "Are you sure you want to delete book?"} %>

<% end %>
<% end %>

Category.rb

    class BooksController < ApplicationController
before_action :find_book, only: [:show, :edit, :destroy, :update]

def index
if params[:category].blank?
@books = Book.all.order("created_at DESC")
else 
    @category_id = Category.find_by(name: params[:category]).id
    @books = Book.where(:category_id => @category_id).order("created_at DESC")
end
end

def show 
end

def new
@book = current_user.books.build
@categories = Category.all.map{ |c| [c.name, c.id]}
end

 def create 
@book = current_user.books.build(book_params)
@book.category_id = params[:category_id]


if @book.save
    redirect_to root_path
else
    render 'new'
    end
end

def edit
@categories = Category.all.map{ |c| [c.name, c.id]}
end

def update
 @book.category_id = params[:category_id]
if @book.update(book_params)
    redirect_to book_path(@book)
else
    render ' new'
end
end

def destroy
    @book.destroy
    redirect_to root_path
end

 private

 def book_params
params.require(:book).permit(:title, :description, :author, :category_id, :book_img)
 end

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


end

Answer 1

如果您必须将类别留空，请使用#try：

<h4>Category: <%= @book.category.try(:name) %></h4>

Answer 2

您需要确保实例@book具有category对象。

<h4>Category: <%= @book.category ? @book.category.name : "This book has no category" %></h4>

Rails4 -undefined方法`name'代表nil：NilClass 4

2 个答案: