code: func (ds *DjangoSession) Update(db XODB) error {
  	var err error
  
  	// if doesn't exist, bail
  	if !ds._exists {
  		return errors.New("update failed: does not exist")
  	}
  
  	// if deleted, bail
  	if ds._deleted {
  		return errors.New("update failed: marked for deletion")
  	}
  
  	// sql query
  	const sqlstr = `UPDATE public.django_session SET (` +
  		`session_data, expire_date` +
  		`) = ( ` +
  		`$1, $2` +
  		`) WHERE session_key = $3`
  
  	// run query
  	XOLog(sqlstr, ds.SessionData, ds.ExpireDate, ds.SessionKey)
  	_, err = db.Exec(sqlstr, ds.SessionData, ds.ExpireDate, ds.SessionKey)
  	return err
  }
docs: // Update updates the DjangoSession in the database.