Formtastic Collection Sorting

I need to sort a collection for formtastic by their state, wether they are selected or not.

My setup looks similar to the following

# user.rb
class User
  has_and_belongs_to_many :colours
end

´

# colour.rb
class Colour
  has_and_belongs_to_many :users

  scope :ordered_for, lambda { |user|
    all.sort_by { |s| include? user ? 1 : 0 }
  }
end

´

# _form.html.haml
= semantic_form_for(@user) do |f|
  = f.input :colours, :as => :check_boxes, :collection => Colour.ordered_for(current_user)

ordered_for returns a well sorted Arr开发者_StackOverflow社区ay. In fact formtastic destroys this order afterwards and sorts the colours by id.

What's a good approach to supres that behaviour? Is there any smarter way to achieve an order by selection?

Thanks in advance!

---

Please try:

Colour.ordered_for(current_user).all