无法将数据从php数组添加到json数据库

I have got problem with array. When i add string to json_encode it save in db but $object give me [{},{},{}]Can you tell me guys what i am doing wrong?

$objects = array();
$objects[] = new Person(1, 'John', 'Smith','java');
$objects[] = new Person(2, 'Stacy', 'Smith','php');

$Db ='./DB.json';
$saveInBase = json_encode($objects);
file_put_contents($Db, $saveInBase);
$loadFromBase = file_get_contents($Db);
$loadFromBase = json_decode($loadFromBase, true);

Please implement JsonSerializable on Person class, you only will have to implement jsonSerialize method, here you have an example:

<?php
class Person implements JsonSerializable
{
    private $id;
    private $name;
    private $last_name;
    private $lang;

    public function __construct($id, $name, $last_name, $lang)
    {
        $this->id = $id;
        $this->name = $name;
        $this->last_name = $last_name;
        $this->lang = $lang;
    }

    public function jsonSerialize()
    {
        return get_object_vars($this);
    }
}

$objects = array();
$objects[] = new Person(1, 'John', 'Smith','java');
$objects[] = new Person(2, 'Stacy', 'Smith','php');

$Db ='./DB.json';
$saveInBase = json_encode($objects);
file_put_contents($Db, $saveInBase);
$loadFromBase = file_get_contents($Db);
$loadFromBase = json_decode($loadFromBase, true);