NoMethodError in Book#show_subjects

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>

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

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

Patrick Doyle wrote: