Stuck on adding category

Question

please help Magento version 2.0.9 I am trying to add categories programmatically . And here my code

    $categoryFactory=self::getObjectManager()->get('\Magento\Catalog\Model\CategoryFactory');
    $categoryTmp = $categoryFactory->create();
    $categoryObj = $categoryTmp->load((int)$categoryDTO->getParentId());
    $categoryTmp = self::getObjectManager()->create('Magento\Catalog\Model\Category');
    $categoryTmp->setPath($categoryObj->getPath())
        ->setParentId((int)$categoryObj->getId())
        ->setName($categoryDTO->getDescription())
        ->setUrlKey($categoryDTO->getUrlKey())
        ->setIsActive(true);
    $createdCategoryId = $categoryTmp->save()      

Which is working and at some point I get

 Fatal error: Uncaught PDOException: SQLSTATE[08004] [1040] Too many connections

But I got categories (not all ) added to magento database with parent-child relationship. After refreshing page it inserts all categories (there is not much left after) ,I am trying to get rid of annoying error so I followed this link this link which is working but again at some poing I get connection error **Besides no category is added to database **. Any tip is welcomed

EDIT 1

  self::getObjectManager()

is this function

 protected static $cachedObjectManager;

public static function getObjectManager()
{
    if(!self::$cachedObjectManager){
        $bootstrap = Bootstrap::create(BP, $_SERVER);
        return $bootstrap->getObjectManager();
    }

    return self::$cachedObjectManager;
}

Answer 1

Looks like you do not store OM in static field

if(!self::$cachedObjectManager){
    $bootstrap = Bootstrap::create(BP, $_SERVER);
    return $bootstrap->getObjectManager();
}

replace it with

if(!self::$cachedObjectManager){
    $bootstrap = Bootstrap::create(BP, $_SERVER);
    return self::$cachedObjectManager = $bootstrap->getObjectManager();
}