How can I use phalcon model to implement optimistic locking?

AFAIK there is no ready-to-use mechanic in Phalcon for this. Your only options are for_update and shared_lock...

Locking may delay a response, but it's still the most robust solution for concurrency. Otherwise, you'll have to implement your own logic for this.

I was missing the ON DUPLICATE KEY UPDATE mechanism, so I've overridden it in the base mysql adapter:

namespace MyProject;

use Phalcon\Db\Adapter\Pdo\Mysql as PhalconMysql;
use Phalcon\Db\Exception;

class Mysql extends PhalconMysql
{
    public function checkConnection() {
        try {
            $this->fetchOne('SELECT 1');
        } catch (\PDOException $e) {
            if (strpos($e->getMessage(), 'MySQL server has gone away') !== false) {
                $this->connect();
            }
        }
    }

    public function ping() {
        $this->checkConnection();
        return $this;
    }

    public function insert($table, array $values, $fields = null, $dataTypes = null) {
        if(count($values)<1) {
            throw new Exception("Unable to insert into " . $table . " without data");
        }
        $placeHolders = [];
        $insertValues = [];
        $bindDataTypes = [];

        foreach($values as $position => $value) {
            if(is_object($value)) {
                $placeHolders[] = (string)$value;
            }
            else {
                if(is_null($value)) {
                    $placeHolders[] = "NULL";
                }
                else {
                    $placeHolders[] = "?";
                    $insertValues[] = $value;
                    if(is_array($dataTypes)) {
                        if(!array_key_exists($position, $dataTypes)) {
                            throw new Exception("Incomplete number of bind types");
                        }
                        $bindDataTypes[] = $dataTypes[$position];
                    }
                }
            }
        }

        $escapedTable = $this->escapeIdentifier($table);

        $joinedValues = join(', ', $placeHolders);
        if(is_array($fields)) {
            $onDuplicate = "ON DUPLICATE KEY UPDATE";
            foreach($this->describeColumns($table) as $col) {
                if($col->isPrimary()) {
                    $f = $this->escapeIdentifier($col->getName());
                    $onDuplicate .= " " . $f . " = LAST_INSERT_ID(" . $f . "),";
                    break;
                }
            }
            $escapedFields = [];
            foreach($fields as $field) {
                $f = $this->escapeIdentifier($field);
                $escapedFields[] = $f;
                $onDuplicate.= " ".$f." = VALUES(".$f."),";
            }
            $onDuplicate = substr($onDuplicate,0,-1);
            $insertSql = "INSERT INTO ".$escapedTable." (".join(", ",$escapedFields).") VALUES (".$joinedValues.") ".$onDuplicate;
        }
        else {
            $onDuplicate = "ON DUPLICATE KEY UPDATE";
            foreach($this->describeColumns($table) as $col) {
                $f = $this->escapeIdentifier($col->getName());
                if($col->isPrimary()) {
                    $onDuplicate .= " " . $f . " = LAST_INSERT_ID(" . $f . "),";
                }
                else {
                    $onDuplicate .= " " . $f . " = VALUES(" . $f . "),";
                }
            }
            $onDuplicate = substr($onDuplicate,0,-1);
            $insertSql = "INSERT INTO ".$escapedTable." VALUES(".$joinedValues.") ".$onDuplicate;
        }
        if(count($bindDataTypes)<1) {
            return $this->execute($insertSql, $insertValues);
        }
        return $this->execute($insertSql, $insertValues, $bindDataTypes);
    }
}