code: func (m *Msg) Update(db *sqlx.DB) error {
  	q := `UPDATE messages SET needstraining=$1 WHERE id=$2`
  	if _, err := db.Exec(q, m.NeedsTraining, m.ID); err != nil {
  		return err
  	}
  	return nil
  }
docs: // Update a message as needing training.