A way to get non-random ids with mongoid based on object characteristics. May be useful for testing purposes (e.g.: mocking Solr indexing with FakeWeb).

derandomizable_id.rb

module DerandomizableId
  extend ActiveSupport::Concern

  included do
    before_create :set_id
  end
  
  def set_id
    attrs = self.attributes
    attrs.delete('_id')
    string = Digest::SHA1.hexdigest(attrs.to_s)[1..24]
    self._id = Moped::BSON::ObjectId.from_string(string)
  end

end