     # Get the ID string and period start timestamp
     _id = @getId identifier, timestamp
     timestamp = @getPeriod(timestamp).toDate()
+    expiry = @getExpiry(timestamp).toDate()
 
     # Build our update increment clause
     update = {}

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

    # Create or update the document
    @findAndModify

      all: 'all'
      events: 'events'
      timestamp: 'timestamp'
      expires: 'expires'

    # Initialize the document superclass
    super collection, mapping
