Be warned of the rather unorthodox behavior of PDOStatement::fetchObject() which injects property-values BEFORE invoking the constructor - in other words, if your class  initializes property-values to defaults in the constructor, you will be overwriting the values injected by fetchObject() !

A var_dump($this) in your __construct() method will reveal that property-values have been initialized prior to calling your constructor, so be careful.

For this reason, I strongly recommend hydrating your objects manually, after retrieving the data as an array, rather than trying to have PDO apply properties directly to your objects.

Clearly somebody thought they were being clever here - allowing you to access hydrated property-values from the constructor. Unfortunately, this is just not how OOP works - the constructor, by definition, is the first method called upon construction. 

If you need to initialize your objects after they have been constructed and hydrated, I suggest your model types implement an interface with an init() method, and you data access layer invoke this method (if implemented) after hydrating.

If you want the constructor to be invoked before `fetchObject` sets the properties then `PDOStatement::fetch` method with `PDO::FETCH_PROPS_LATE` argument should be used.

It should be mentioned that this method can set even non-public properties. It may sound strange but it can actually be very useful when creating an object based on mysql result.
Consider a User class:

<?php
class User {
   // Private properties
   private $id, $name;

   private function __construct () {}

   public static function load_by_id ($id) {
      $stmt = $pdo->prepare('SELECT id, name FROM users WHERE id=?');
      $stmt->execute([$id]);
      return $stmt->fetchObject(__CLASS__);
   }
   /* same method can be written with the "name" column/property */
}

$user = User::load_by_id(1);
var_dump($user);
?>

fetchObject() doesn't care about properties being public or not. It just passes the result to the object. Output is like:

object(User)#3 (2) {
  ["id":"User":private]=>
  string(1) "1"
  ["name":"User":private]=>
  string(10) "John Smith"
}

PDOStatement::fetchObject() injects values as string, I needed a conversion type.

I did it including settype() function in class constructor

Below method that find an user by id and return user object instance:

<?php
class UserMapper extends MapperAbstract
{
    //other code
    public function findById(int $userId)
    {
        $pdos = $this->dBase->prepare('SELECT user_id AS objectId, name, description, password, active, created, 
        last_update AS lastUpdate FROM user WHERE user_id = :id');

        $pdos->bindParam(':id', $userId, \PDO::PARAM_INT);
        $pdos->execute();

        return $pdos->fetchObject('\DomainObjects\User', array($this->password));
    }
    //other code
}
?>

User class with type handling:

<?php
class User extends DomainObjectAbstract
{
   //other code
    public function __construct(Password $password)
    {
        $this->passwordUtility = $password;
        
        settype($this->objectId, 'integer');
        settype($this->active, 'integer');
    }
    //other code
}
?>

var_dump() of returned User instance:

<?php
object(DomainObjects\User)[18]
  public 'name' => string 'root' (length=4)
  public 'description' => string 'System User' (length=11)
  public 'password' => string '$2y$11$4IAn6SRaB0osPz8afZC5D.CmTrBGxnb5FQEygPjDirK9SWE/u8YuO' (length=60)
  public 'active' => int 1
  public 'created' => string '2015-02-14 10:39:00' (length=19)
  public 'lastUpdate' => string '2016-08-30 18:46:56' (length=19)
  private 'passwordUtility' => 
    object(Auth\Password)[13]
      protected 'options' => 
        array (size=1)
          'cost' => int 11
  protected 'objectId' => int 1
?>

'objectId' and 'active' are now of the type required

You can access MySQL tables in an objective way. Suppose you have a table named Users that has fields: UserID, UserName, UserPassword, UserBirthday, you can create a PHP class extending DataObject that is associated with this table:
<?php 
class User extends DataObject {
    // name: Table Name, key: Primary Key (can be an array), auto: AUTO_INCREMENT field
    protected static $_table = array('name' => 'Users', 'key' => 'UserID', 'auto' => 'UserID');
    // relationships between PHP properties and MySQL field names
    protected static $_propertyList = array('id' => 'UserID', 'name' => 'UserName', 'password' => 'UserPassword', 'birthday' => 'UserBirthday');
    
    // A method that fetches all users as an array
    public static function GetAll() {
        global $dbh;
        $sql = 'SELECT * FROM Users';
        $stmt = $dbh->query($sql);
        $users = array();
        while ($user = $stmt->fetchObject(__CLASS__)) {
            $users[] = $user;
        }
        return $users;
    }
    // Methods that fetch a specific user
    public static function GetUserByName($name) {}
    public static function GetUserByID($name) {}
    
    // Methods for the current user object
    public function checkPassword($password) {return $this->password == $password;}
    public function showLink() {return "<a href=\"user.php?i={$this->id}\">{$this->name}</a>";}
}

// Then, you can create an instance of this class to insert a row in your table
$user = new User();
$user->name = 'oct1158';
$user->password = '789012';
$user->useFunction('birthday', 'NOW()');
echo 'Field birthday uses MySQL Function: ', $user->birthday, '<br>';
if ($user->insert()) {
    echo 'New User ID: ', $user->id, '<br>';
    
    // Update the row
    $user->password = '112233';
    $user->update();
} else {
    echo 'INSERT Failed<br>';
}
// Get a specific user by a query
$sql = 'SELECT * FROM Users WHERE UserName = ?';
$stmt = $dbh->prepare($sql);
$stmt->execute(array('admin'));
$admin_user = $stmt->fetchObject('User');
echo 'Admin ID is ', $admin_user->id, '.<br>';
echo 'Admin Birthday is ', $admin_user->birthday, '.<br>';

// Get all users by a static method of that class
$users = User::GetAll();
echo '<br>';
echo $users[0]->name, ', ', $users[0]->birthday, '<br>';
echo $users[1]->name, ', ', $users[1]->birthday, '<br>';
echo $users[2]->name, ', ', $users[2]->birthday, '<br>';
echo '<br>';

// Create an empty user and then delete it immediately
$user = new User();
$user->insert();
$user->delete();
?>
The DataObject class example:
<?php 
class DataObject {
    private $changedFields = array(); // list of updated fields
    private $data = array(); // original row from PDOStatement
    private $funcFields = array(); // fields that use MySQL functions
    // The properties above are private in this class, so even if in your subclass you define some properties named the same, or you associate a property of the same name with a field in your table, they will never influence these properties.
    function __get($property) {
        if (isset($this::$_propertyList[$property])) {
            return $this->data[$this::$_propertyList[$property]]; // access fields by PHP properties
        } else {
            return $this->$property; // throw the default PHP error
        }
    }
    function __set($property, $value) {
        if (isset($this::$_propertyList[$property])) {
            $field = $this::$_propertyList[$property];
            $this->data[$field] = $value; // update $data
            
            // take down changed fields
            if (!in_array($field, $this->changedFields)) {
                array_push($this->changedFields, $field);
            }
            $index = array_search($field, $this->funcFields);
            if ($index !== false) {
                unset($this->funcFields[$index]);
                $this->funcFields = array_values($this->funcFields);
            }
        } else {
            // For fetchObject
            $this->data[$property] = $value; // redirect to Array $data
        }
    }
    private function checkPrimaryKey() {}
    private function clear() {}
    public function delete() {}
    public function insert() {}
    public function update() {}
    public function useFunction($property, $function) {}
}
?>

If using a namespaced class, you must provide the fully qualified class name; fetchObject does not seem to know about any "use" statements.

This results in a PHP Fatal error: Class 'MyClass' not found...:
<?php
use MyNamespace\MyClass;
// ...
$o = $statement->fetchObject('MyClass'));
?>
This works:
<?php
use MyNamespace\MyClass; //still needed for my code
// ...
$o = $statement->fetchObject('MyNamespace\\MyClass'));
?>