PHP İl - ilçe listeleme nasıl yapılır?

<link rel="stylesheet" href="assets/sweetalert2.css">
<link rel="stylesheet" href="assets/css/adres-sayfasi.css">
<script src="assets/main.js"></script>

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css">

<script src="https://code.jquery.com/jquery-3.5.1.slim.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/@popperjs/core@2.5.3/dist/umd/popper.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.5.2/js/bootstrap.min.js"></script>

<div class="card shadow mb-4">
    <div class="card-header py-3">
        <h6 class="m-0 font-weight-bold text-primary"><a href="/">Ana Sayfa</a> > <a href="/adres">Adres İşlemleri</a></h6>
    </div>

    <div class="card-body">
        <form onsubmit="adres_ekle(event)">
            <input type="hidden" name="id" value="<?php echo $user->id ?>">
            <div class="form-group">
                <label for="baslik">Adres Başlığı:</label>
                <input type="text" class="form-control" id="baslik" name="baslik" required>
            </div>
            <br>

            <div class="form-row">
                <div class="form-group col-md-6">
                    <label for="il">İl:</label>
                    <select onchange="getIlce(event)" class="form-control" id="il" name="il" required>
                        <option value="">İl Seçin</option>
                        <?php
                        $iller = DB::get("SELECT * FROM iller");
                        if (!empty($iller)) {
                            foreach ($iller as $il) {
                                echo "<option value='" . $il->id . "'>" . $il->sehiradi . "</option>";
                            }
                        }
                        ?>
                    </select>
                </div>
                <div class="form-group col-md-6">
                    <label for="ilce">İlçe:</label>
                    <select class="form-control" id="ilce" name="ilce" required>
                        <option value="">İlçe Seçin</option>
                    </select>
                </div>
            </div>
            <br>

            <div class="form-row">
                <div class="form-group col-md-6">
                    <label for "mahalle">Mahalle:</label>
                    <select class="form-control" id="mahalle" name="mahalle" required>
                        <option value="">Mahalle Seçin</option>
                    </select>
                </div>
                <div class="form-group col-md-6">
                    <label for="sokak">Sokak:</label>
                    <input type="text" class="form-control" id="sokak" name="sokak" required>
                </div>
            </div>
            <br>

            <div class="form-row">
                <div class="form-group col-md-6">
                    <label for="kat">Kat:</label>
                    <input type="text" class="form-control" id="kat" name="kat">
                </div>
                <div class="form-group col-md-6">
                    <label for="kapi_no">Kapı No:</label>
                    <input type="text" class="form-control" id="kapi_no" name="kapi_no" required>
                </div>
            </div>
            <br>

            <div class="form-row">
                <div class="form-group col-md-6">
                    <label for="daire">Daire:</label>
                    <input type="text" class="form-control" id="daire" name="daire">
                </div>
                <div class="form-group col-md-6">
                    <label for="aciklama">Ek Açıklama:</label>
                    <textarea class="form-control" id="aciklama" name="aciklama"></textarea>
                </div>
            </div>
            <br>

            <div class="text-right">
                <input type="submit" class="btn btn-primary" value="Adresi Kaydet">
            </div>
        </form>
    </div>
</div>

<script>
    const getIlce = (event) => {
        console.log(event.currentTarget.value);
    }
</script>

<html>
<head>
    <title>İl ilçe PDO</title>
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css">
</head>

<body>


<div class="container">
    <div class="row">
        <div class="col-md-12"><h1>PHP PDO ve MySQL ile il ilçe seçme</h1><hr></div>


        <div class="col-md-3">
            <label for="il">İl</label>
            <select name="il" id="il" class="form-control" >
                <option value="">Seçin...</option>
            </select>
        </div>

        <div class="col-md-3">
            <label for="ilce">İlçe</label>
            <select name="ilce" id="ilce" class="form-control" disabled="disabled">
                <option value="">Seçin...</option>
            </select>
        </div>
    </div>
</div>

<script src="https://code.jquery.com/jquery-1.12.4.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js"></script>

<script>
    $(document).ready(function(){
        ajaxFunc("il", "0", "#il");


        $("#il").on("change", function(){

            $("#ilce").attr("disabled", false).html("<option value=''>Seçin..</option>");
            console.log($(this).val());
            ajaxFunc("ilce", $(this).val(), "#ilce");

        });

        function ajaxFunc(action, name, id ){
            $.ajax({
                url: "ajax.php",
                type: "POST",
                data: {action:action, name:name},
                success: function(sonuc){
                    $.each($.parseJSON(sonuc), function(index, value){
                        var row="";
                        row +='<option value="'+value+'">'+value+'</option>';
                        $(id).append(row);
                    });
                }});
        }
    });
</script>
</body>
</html>

<?php
include ("dbConn.php");

$action=$_POST["action"];

switch ($action)
{

    case "il":
        $db=new dbConn();
        $bolge=$_POST["name"];
        return $db->getIlList($bolge);
        break;

    case "ilce":
        $db=new dbConn();
        $il=$_POST["name"];
        return $db->getIlceList($il);
        break;
}

<?php
class dbConn
{
    protected static $db;


    //veritabanına bağlanan fonksiyon
    public function __construct()
    {
        try{
            self::$db = new PDO("mysql:host=localhost;dbname=ililce;charset=utf8", "root", "");
        }
        catch (PDOException $exception)
        {
            print $exception->getMessage();
        }
    }


    //İlleri getiren fonksiyon
    public function getIlList($bolge){
        $data=array();
        $query = self::$db->prepare("SELECT DISTINCT il FROM ilveilceler WHERE bolge=:bolge");
        $query->execute(array(":bolge"=>$bolge));
        if($query->rowCount())
        {
            foreach ($query as $row)
            {
                $data[]=$row["il"];
            }
        }
        echo json_encode($data);
    }


    //İlçeleri getiren fonksiyon
    public function getIlceList($il){
        $data=array();
        $query = self::$db->prepare("SELECT DISTINCT ilce FROM ilveilceler WHERE il=:il");
        $query->execute(array(":il"=>$il));
        if($query->rowCount())
        {
            foreach ($query as $row)
            {
                $data[]=$row["ilce"];
            }
        }
        echo json_encode($data);
    }
}