example.go

// example of using a txn

import "github.com/pkg/errors"
import "database/sql"

// ...

// UpdateUserEmailAddress updates a user's email address and adds a user event, or returns an error
func (ds *Datastore) UpdateUserEmailAddress(id uint64, emailAddress string) (err error) {
  tx, err := ds.db.BeginTx(ctx, &sql.TxOptions{Isolation: sql.LevelSerializable})
  if err != nil {
    return errors.Wrap(err, "error starting txn")
   }
  defer func() {
    if err != nil {
      _ = tx.Rollback()
    }
  }()
  _, execErr := tx.Exec(`UPDATE users SET email = ? WHERE id = ?;`, emailAddress, id)
  if execErr != nil {
    return errors.Wrap(err, "error updating users record")
  }
  _, execErr = tx.Exec(`INSERT INTO user_events (id, event_msg) VALUES (?,?);`, id, "email updated to "+emailAddress)
  if execErr != nil {
    return errors.Wrap(err, "error adding user event")
  }
  if err := tx.Commit(); err != nil {
    return errors.Wrap(err, "error committing txn")
  }
  return nil
}