Fat-Free Framework: Mapper with ONLOAD event and custom derived non-virtual fields

example.php

<?php

/**
 * This snippet is part of an answer to a StackOverflow question
 * and is executable as soon as line 11 gets corrected
 * to include Fat-Free Framework's `base.php` file.
 *
 * @see http://stackoverflow.com/questions/41840876/using-computed-properties-on-fatfree-mapper-object-not-retrieved-from-database
 */

require_once '../../base.php';

/**
 * @property string title
 */
class TestMapper extends \DB\SQL\Mapper {
    /**
     * Custom mapper field which isn't backed and persisted by the database.
     *
     * @var null|string
     */
    public $upper_title;

    /**
     * @param \DB\SQL $sql
     */
    public function __construct(\DB\SQL $sql) {
        parent::__construct($sql, 'test');

        $this->onload(function (TestMapper $mapper) {
            $mapper->upper_title = strtoupper($mapper->title);
        });
    }
}

// Create SQL environment.
{
    $dbFile = 'test.sqlite';

    // Reset environment.
    if (is_file($dbFile)) {
        unlink($dbFile);
    }

    $sql = new DB\SQL('sqlite:' . $dbFile);

    $sql->exec('CREATE TABLE test(title TEXT)');
    $sql->exec('INSERT INTO test (title) VALUES ("Hello World")');

    /**
     * Not compatible with tag `3.5.0`.
     *
     * > $mapper = new TestMapper($sql);
     * > $mapper->title = 'Hello World';
     * > $mapper->save();
     */

    unset($dbFile);
}

$mapper = new TestMapper($sql);

for ($mapper->load(); !$mapper->dry(); $mapper->next()) {
    printf("title:       %s\n", $mapper->title);
    printf("upper_title: %s\n", $mapper->upper_title);
}

result.txt

title:       Hello World
upper_title: HELLO WORLD