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>
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