I try to learn the has_and_belongs_to_many relationship between my 2 fresh new and simple models Product and Author, where a Product can have many authors and where author can have a lots of products.

I wrote this :

class Author < ActiveRecord::Base
  has_and_belongs_to_many :products
end

class Product < ActiveRecord::Base
  has_and_belongs_to_many :authors
end

In the partial form of view for the products, I have :

<p>Products</p>
<%= collection_select(:product, :author_ids, @authors, :id, :name, :prompt => " ",  :multiple => true) %>

but when I hit the update button, I get this strange message I can't resolve myself :

NoMethodError in ProductsController#update undefined method `reject' for "1":String

Rails.root: /home/stephane/www/HABTM Application Trace | Framework Trace | Full Trace app/controllers/products_controller.rb:63:in block in update' app/controllers/products_controller.rb:62:inupdate' Request

Parameters: {"utf8"=>"✓", "_method"=>"put", "authenticity_token"=>"2GlTssOFjTVZ9BikrIFgx22cdTOIJuAB70liYhhLf+4=", "product"=>{"title"=>"Le trésor des Templiers", "original_title"=>"", "number"=>"1", "added_by"=>"", "author_ids"=>"1"}, "commit"=>"Update Product", "id"=>"1"}

What's wrong ? Is there a problem with :product_ids... I saw on internet I had to pu a "s" but I'm not sure of what it represents....

How can I link the table authors_products to the key which is given back by the drop-down menu ? (here "author_ids"=>"1") Thx !