Getting error while studying rails

Hello, I was going through the tutorial in this link:

Wehn I came to section 6.2, I added the link using following code
<%= link_to "My Blog", posts_path %>
and I get this error:
undefined local variable or method `posts_path' for #<ActionView::Base:

Couldn't figure where I have gone wrong. Any help?

Thanks in advance.

Got answr by googling. I must add

map.resource :posts

in congfig/routes.rb