Reordering embedded documents in Mongoid

One of the great things about embedded documents in MongoDB is that you can design your "schema" according to how you're going to use the data. Ordered lists of objects is a great use for embedded documents, as you can just shove objects in an array and read them out in order. This allows one to dispense with the unpleasantness of "acts_as_list"-style approaches where you have to juggle a "position" field and do an explicit sort.

But what if you want to reorder the embedded documents? Should be simple to sort an array. Our ODM - Mongoid in this case - would never represent the embedded collection as an array and not let us work with it as an array, right?

class Container
    include Mongoid::Document
    embeds_many :items
end

class Item
    include Mongoid::Document
    embedded_in :container

    field :title, :as => String
end

c = Container.create
c.items.create :title => "first"
c.items.create :title => "second"

>> c.items
=> [#<Item _id: 4dd2d971322bcdab7c000003, title: "first", _id: BSON::ObjectId('4dd2d971322bcdab7c000003'), _type: nil>, #<Item _id: 4dd2d981322bcdab7c000004, title: "second", _id: BSON::ObjectId('4dd2d981322bcdab7c000004'), _type: nil>]
>> c.items.reverse!
=> [#<Item _id: 4dd2d981322bcdab7c000004, title: "second", _id: BSON::ObjectId('4dd2d981322bcdab7c000004'), _type: nil>, #<Item _id: 4dd2d971322bcdab7c000003, title: "first", _id: BSON::ObjectId('4dd2d971322bcdab7c000003'), _type: nil>]
>> c.save
=> true
>> c.reload.items
=> [#<Item _id: 4dd2d971322bcdab7c000003, title: "first", _id: BSON::ObjectId('4dd2d971322bcdab7c000003'), _type: nil>, #<Item _id: 4dd2d981322bcdab7c000004, title: "second", _id: BSON::ObjectId('4dd2d981322bcdab7c000004'), _type: nil>]

OK, so not that easy, but maybe this means we just need to set the new array explicitly.

>> c.items = c.items.reverse
=> []

Yikes. So we can treat it as an array as much as we want - as long as we don't need to persist it. Keep in mind this is a MongoDB trait, not a failing of the ODM per se (though one would expect the ODM to help us out here!).

So what do we do? Well, I worked around it by explicitly rebuilding the array of embedded documents:

>> reordered_items = c.items.reverse
=> [#<Item _id: 4dd2e0b7322bcdae0d000002, title: "second", _id: BSON::ObjectId('4dd2e0b7322bcdae0d000002'), _type: nil>, #<Item _id: 4dd2e0b6322bcdae0d000001, title: "first", _id: BSON::ObjectId('4dd2e0b6322bcdae0d000001'), _type: nil>]
>> c.items.clear
=> []
>> reordered_items.each { |i| c.items.create i.attributes }
=> [#<Item _id: 4dd2e0b7322bcdae0d000002, title: "second", _id: BSON::ObjectId('4dd2e0b7322bcdae0d000002'), _type: nil>, #<Item _id: 4dd2e0b6322bcdae0d000001, title: "first", _id: BSON::ObjectId('4dd2e0b6322bcdae0d000001'), _type: nil>]
>> c.reload.items
=> [#<Item _id: 4dd2e0b7322bcdae0d000002, title: "second", _id: BSON::ObjectId('4dd2e0b7322bcdae0d000002'), _type: nil>, #<Item _id: 4dd2e0b6322bcdae0d000001, title: "first", _id: BSON::ObjectId('4dd2e0b6322bcdae0d000001'), _type: nil>]

This works for me, but it's not very elegant. Any problems with this approach? Feel free to let me know.