HABTM, select box and array issue

Product model is as follows [code] class Product < ActiveRecord::Base   belongs_to :product_category   has_and_belongs_to_many :variant_parameters [/code]

I am displaying a collection of variant parameters for the product. Can be more than one selection box. I want to update the same.

I currently have the following selection code [code] <%= collection_select(:product, :variant_parameter_ids, @product_categories_variants_parameters, :id, :parameter, {:prompt => true}) %> [/code]

I have more than one drop down of variant params associated to the product.

How do I specify that I need :variant_parameter_ids and not :variant_parameter_ids ?

When I try it I get [code]undefined method `' for :variant_parameter_ids:Symbol[/code]

Can someone respond please ?