class ActiveFedora::Base

def add_datastream(datastream, opts={})

@returns DSID of the added datastream
:prefix option will set the prefix on auto-generated DSID
If datastream does not have a DSID, a unique DSID is generated
Adds datastream to the object. Saves the datastream to fedora upon adding. 
def add_datastream(datastream, opts={})
  datastream.pid = self.pid
  if datastream.dsid == nil || datastream.dsid.empty?
    prefix = opts.has_key?(:prefix) ? opts[:prefix] : "DS"
    datastream.dsid = generate_dsid(prefix)
  end
  datastreams[datastream.dsid] = datastream
  return datastream.dsid
end