Insert mongo with AutoIncrement

insertNew.php

$itemid = $this->Counter->seq('itemid');
$itemArray = [ "_id" => $itemid['value']['seq'],
  "title" => 'hogehoge',
  "user_id" => 1,
  "created" => date('Y-m-d H:i:j'),
];

function add($itemArray) {
$client = new MongoClient();
$db = $client->selectDB('databaseName');
$col = $db->selectCollection('item');
$col->insert( $itemArray );
}