While you are creating the Product, you are not creating and
associating the Categories, or populating the instance variable for
the view.
Try something like:
Controller
def create
@product = Product.new(params[:product])
if @product.save
@category = @product.category # Add this line.
flash[:notice] = 'Product was successfully created.'
redirect_to :action => 'timeframe'
else
render :action => 'new'
end
end
