Rails - Jan 2006 - recipes/categories to books/authors but listing doesn''t work

People,

I have gone through the cookbook example:

http://www.onlamp.com/pub/a/onlamp/2005/01/20/rails.html?page=1

and everything worked fine an a FC4/Postgres setup.

I then tried to reproduce this success with something that would be
useful to me - a library db using books & authors tables.  The author
list works but NOT the book list (unless I take line #17 out).

I get this message:


Showing app/views/book/list.rhtml where line #17 raised: 

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

Extracted source (around line #17):

14:  <% @books.each do |book| %>
15:   <tr>
16:    <td><%= link_to book.title, :action => "show", :id
=> book.id %></td>
17:    <td><%= book.author.last_name %></td>
18:   </tr>
19:  <% end %>
20: </table>


but as far as I can tell I have done the right things in the
controllers, models and views:

author_controller.rb:

    @authors = Author.find  :all,
                            :order => ''last_name,
first_name''

book_controller.rb:

    @books = Book.find  :all,
                        :order => ''title, back''

author.rb:

    has_many :books

book.rb:

    belongs_to :author

book/list.rhtml:

<table border="0">
 <tr>
  <td width="60%"><p
align="left"><i><b>Book</b></i></td>
  <td width="20%"><p
align="left"><i><b>Author</b></i></td>
 </tr>

 <% @books.each do |book| %>
  <tr>
   <td><%= link_to book.title, :action => "show", :id
=> book.id %></td>
   <td><%= book.author.last_name %></td>
  </tr>
 <% end %>
</table>

authors table:

 id         | integer               | not null default
nextval(''public.authors_id_seq''::text)
 last_name  | character varying(20) |
 first_name | character varying(20) |
 other_name | character varying(20) |

books table:

 id        | integer               | not null default
nextval(''public.books_id_seq''::text)
 media     | character(2)          | not null
 title     | character varying(50) | not null
 year      | integer               | not null
 cat       | character(1)          | not null
 back      | character(1)          |
 own       | character(1)          |
 author_id | integer           


I have been battling with this for ages but can''t see any bugs left -
any suggestions?

Thanks,

Phil.

-- 
Philip Rhoades

Pricom Pty Limited  (ACN 003 252 275  ABN 91 003 252 275)
GPO Box 3411
Sydney NSW      2001
Australia
Mobile:  +61:(0)411-185-652
Fax:     +61:(0)2-8221-9599
E-mail:  phil@pricom.com.au

Philip Rhoades <phil@...> writes:
          
> I have been battling with this for ages but can''t see any bugs
left -
> any suggestions?
It would appear that you have a book with no author.

replace the stuff in your view with

<%=book.inspect%>

and see if any book has a nil author.

-damon
http://damonclinkscales.com/