无法使用getSelect()->where()Magento 2从数据库中筛选数据

我目前正在使用magento 2.2.1,我遇到了一个奇怪的问题。我试图从数据库中获取一组数据,并将其显示在管理网格上。我想记录特定代理ID的记录,以便有一个具有代理ID值的变量。当我将此变量作为参数传递给 $this->collection->getSelect()->where('agent_id = ?', $this->givenAgentId); 它不会显示任何内容,但如果我替换$this->givenAgentId的值,例如4,它工作得很好!

这是我的班级:

<?php
namespace vendor\plugin\Ui\Component\Listing\DataProviders\Atisstats\Coupons;

use \vendor\plugin\Model\ResourceModel\Coupons\CollectionFactory;
use \Magento\Framework\Registry;

class Listing extends \Magento\Ui\DataProvider\AbstractDataProvider {

protected $_registry;

protected $givenAgentId = 0;

public function __construct(
    Registry $registry,
    $name,
    $primaryFieldName,
    $requestFieldName,
    CollectionFactory $collectionFactory,
    array $meta = [],
    array $data = []
) {
    parent::__construct($name, $primaryFieldName, $requestFieldName, $meta, $data);

    $this->_registry = $registry;

    $objectManager = \Magento\Framework\App\ObjectManager::getInstance();
    $resource = $objectManager->get('\Magento\Framework\App\ResourceConnection');
    $connection = $resource->getConnection();
    $select = $connection->select()
        ->from(
            ['amasty_perm_dealer'],
            ['user_id']
        );
    $data = $connection->fetchAll($select);

    foreach ($data as $dealerId) {
        if ($dealerId['user_id'] == $this->_registry->registry('admin_session_id')) {
            $this->givenAgentId = intval($this->_registry->registry('admin_session_id'));
        }
    }

    if ($this->givenAgentId != 0) {
        $this->collection->getSelect()->where('agent_id = ?', $this->givenAgentId);
    } else {
        $this->collection = $collectionFactory->create();
    }

}

}

我已经在这里呆了几个小时了!