       all: 'all'
       events: 'events'
       timestamp: 'timestamp'
+      expires: 'expires'
 
     # Initialize the document superclass
     super collection, mapping

  getId: (identifier, timestamp) ->
    timestamp = @getTimestamp timestamp
    "#{identifier}#{@options.id_mark}#{_pad timestamp, 15}"

  ###
  # Record events

    # Set our period timestamp on the document
    updateTimestamp = {}
    updateTimestamp[@timestamp] = timestamp
    updateTimestamp[@expires] = expiry

    # Create or update the document
    @findAndModify
