Integer sequence ids in Mongo

sequence.rb

Mongoid.database.add_stored_function "sequence", <<-__
  function(name) {
    var ret = db.counters.findAndModify({ query: { _id: name}, update: { $inc : { next: 1}}, "new" :true, upsert: true});
    return ret.next;
  }
__

class Sequence
  include Mongoid::Fields::Serializable

  def deserialize(object)
    object.to_i
  end

  def serialize(object)
    Mongoid.master.eval("sequence('#{object}')").to_i
  end
end

class A
  include Mongoid::Document
  field :_id, :type => Sequence
end

A.create(:_id => "as")

yes i can understand that. somewhat humorously i have actually had AR projects configured so that it assignes ids up front to make circular associations simpler ;-)

you know, top level ids and intra-document ids are not really the same thing.... i've considered before both having nice ids on top level docs and object_ids for intra-document relations...

in the end it is indeed very difficult to beat the overall tradoffs object_ids provide. lately i've just been slugging the top level namespace in my urls, for instance

/dojo4/posts/comments/$object_id

and that addresses the 80% rule pretty well.