Rails3, Datamapper and select

Hi all, I'm testing rails3 with Datamapper on a simple project.

I've 2 classes : class Societe   include DataMapper::Resource

  property :id, Serial   property :nom, String   property :adresse, Text

  has n, :clients end

class Client   include DataMapper::Resource

  property :id, Serial   property :prenom, String   property :nom, String   property :telephone, String   property :courriel, String   property :adresse, Text   property :view_only, Boolean

  belongs_to :societe end

I created them using rails generate scaffold (except belongs/ has of course).

I've then have in the folder "view" 5 erb templates per class, and especially one (_form) used by "new" and "edit" templates. In order to select the society, I have added in client's _form a select:

<%= form_for(@client) do |f| %>   <%= f.error_messages %> ... <div class="field">     <%= f.label :societe %><br />     <%= f.select(:societe_id, @societes.map{|s| [s.nom, s.id]}) %>   </div>   <div class="actions">     <%= f.submit %>   </div> <% end %>

In creation mode, everything is allright and the customer is created with the link to its society But when I edit, I have the following error:

Showing /home/.../app/views/clients/_form.html.erb where line #30 raised:

undefined method `societe_id' for #<Client:0xa51833c>

Extracted source (around line #30):

27: </div> 28: <div class="field"> 29: <%= f.label :societe %><br /> 30: <%= f.select(:societe_id, @societes.map{|s| [s.nom, s.id]}) %> 31: </div> 32: <div class="actions"> 33: <%= f.submit %>

Any idea why it's working with empty "client" and not with existing one?

Thanks in advance,