Select in rails 2

Hi all,

Im facing problem with select in rails.

I have providers and categories…

they have a joining table providers_categories where i store both
provider_id and category_id.

In new page I have the multiple select for categories while creating a
provider like this… Im using haml

= select(:provider, :provider_category_id,
ProviderCategory.all.collect{|p| [p.name, p.id,]}, {},
{:multiple=>true})

But while editing, The select tag should display all the selected
categories to be selected default…

I dont know how to do this…

Please help me in this…

Regards,

P.Angel