NoMethodError in Book#show_subjects

rubyonrails-talk
1

Hi,

I am quite new to ROR.I am trying to create a rails simple application that has informations about Books and Subjects.Srangely, I finished creating a basic application, and it worked fine. But then , I just tried to add some more values in the database, and faced problem with migration, that just made me crazy. SO I deleted the database and did the database and migration thing all over again without touching rest of the codes.Now the application runs, but when I click on the subject name, it show error, although it was working well before.Can someone help me please in this regards ???

The ERROR is :

NoMethodError in Book#show_subjects

Showing book/show_subjects.rhtml where line #1 raised:

You have a nil object when you didn't expect it! The error occurred while evaluating nil.name

Extracted source (around line #1):

1: <h1><%= @subject.name -%></h1> 2: <ul> 3: <% @subject.books.each do |c| %> 4: <li><%= link_to c.title, :action => "show", :id => c.id -%></li>

I have two tables in my database : books and subjects

The Controller is

class BookController < ApplicationController   layout 'standard'   def list

    @books = Book.find(:all)   end

  def show

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

  def new     @book = Book.new     @subjects = Subject.find(:all)   end

  def create     @book = Book.new(params[:book])     if @book.save       redirect_to :action => 'list'     else       @subjects = Subject.find(:all, :order => "name")       render :action => 'new'     end   end

  def edit

    @book = Book.find(params[:id])     @subjects = Subject.find(:all)   end

  def update     @book = Book.find(params[:id])     if @book.update_attributes(params[:book])       redirect_to :action => 'show', :id => @book     else       @subjects = Subject.find(:all)       render :action => 'edit'     end   end

  def delete     Book.find(params[:id]).destroy     redirect_to :action => 'list'   end

  def show_subjects     @subjects = Subject.find(params[:id])

  end

end

The show_subjects.rhtml file is :

<h1><%= @subject.name -%></h1> <ul> <% @subject.books.each do |c| %> <li><%= link_to c.title, :action => "show", :id => c.id -%></li> <% end %> </ul>

2

The Controller is

class BookController < ApplicationController

layout ‘standard’

def show_subjects

@subjects = Subject.find(params[:id])

end

end

The show_subjects.rhtml file is :

<%= @[subject.name](http://subject.name) -%>

    <% @subject.books.each do |c| %>

  • <%= link_to c.title, :action => "show", :id => [c.id](http://c.id) -%>

    • <% end %>

I don’t know if this is a typo in your post or not, but your #show_subjects method sets the “@subjects” (note the plural) instance variable whereas your view references the “@subject” (note – singular) instance variable.

–wpd

3

Thanks a lot Patrick, it works now!!! thanks a lot.

Patrick Doyle wrote: