code: func (ds *DjangoSession) Insert(db XODB) error {
  	var err error
  
  	// if already exist, bail
  	if ds._exists {
  		return errors.New("insert failed: already exists")
  	}
  
  	// sql query
  	const sqlstr = `INSERT INTO django.django_session (` +
  		`session_data, expire_date` +
  		`) VALUES (` +
  		`:1, :2` +
  		`) RETURNING session_key /*lastInsertId*/ INTO :pk`
  
  	// run query
  	XOLog(sqlstr, ds.SessionData, ds.ExpireDate, nil)
  	res, err := db.Exec(sqlstr, ds.SessionData, ds.ExpireDate, nil)
  	if err != nil {
  		return err
  	}
  
  	// retrieve id
  	id, err := res.LastInsertId()
  	if err != nil {
  		return err
  	}
  
  	// set primary key and existence
  	ds.SessionKey = string(id)
  	ds._exists = true
  
  	return nil
  }
docs: // Insert inserts the DjangoSession to the database.