Magento2 addFieldToFilter调用使用硬编码值但不具有相同值的变量

I'm building the admin for a Magento2 store (currently on 2.1.7, they want to use the newest version until we go live and then want to stabilize a particular version). The module in question is supposed to display all existing orders, with an actionsColumn that contains links to cancel, edit, and open a detailed overview of the purchased items associated with that order. The order detail page contains a grid view that should display all order items associated with an order number passed in the URL.

In order to filter out Order Items that don't relate to the specific Order Number, I've extended the \Magento\Framework\View\Element\UiComponent\DataProvider\SearchResult class. This works except for one weird caveat. If, in the addFieldToFilter call, I replace $ordNum with, say, '10000', it grabs the correct data. When using $ordNum to call this dynamically, however, it returns no rows at all. This despite trying all sorts of casting and === checks to ensure that there's no difference between the hardcoded and dynamic values. Is this a Magento bug? I can't at all figure out why this would be the case.

<?php


class OrderItems extends \Magento\Framework\View\Element\UiComponent\DataProvider\SearchResult
{

    protected function _initSelect()
    {        
        $this->filterByOrderNum();

        parent::_initSelect();

        return $this;
    }

    private function filterByOrderNum()
    {
        $request = \Magento\Framework\App\ObjectManager::getInstance()
                       ->get('Magento\Framework\App\Request\Http');

        $ordNum = $request->getParam('order_num');

        $this->addFieldToFilter('order_num', ['eq' => $ordNum]); //if I switch this to hardcoded 10000, this works. With the variable, no dice.

        return $this;
    }
}

Try this in place of the getParam statement:

$url = parse_url($request);
$path =  explode('/',$url['path']);
$ordNum = $path[3];

Just to make sure we are on the same page, this is the full code:

<?php


class OrderItems extends \Magento\Framework\View\Element\UiComponent\DataProvider\SearchResult
{

    protected function _initSelect()
    {        
        $this->filterByOrderNum();

        parent::_initSelect();

        return $this;
    }

    private function filterByOrderNum()
    {
        $request = \Magento\Framework\App\ObjectManager::getInstance()
                       ->get('Magento\Framework\App\Request\Http');

        $url = parse_url($request);
        $path =  explode('/',$url['path']);
        $ordNum = $path[3];

        $this->addFieldToFilter('order_num', $ordNum); //if I switch this to hardcoded 10000, this works. With the variable, no dice.

        return $this;
    }
}

We have solved this issue by doing the following :

/**
 * CcCustompriceProductListingDataProvider constructor.
 * @param string $name
 * @param string $primaryFieldName
 * @param string $requestFieldName
 * @param \Magento\Framework\Api\Search\ReportingInterface $reporting
 * @param \Magento\Framework\Api\Search\SearchCriteriaBuilder $searchCriteriaBuilder
 * @param \Magento\Framework\App\RequestInterface $request
 * @param \Magento\Framework\Api\FilterBuilder $filterBuilder
 * @param array $meta
 * @param array $data
 * @throws \Exception
 */
public function __construct(
    $name,
    $primaryFieldName,
    $requestFieldName,
    ReportingInterface $reporting,
    SearchCriteriaBuilder $searchCriteriaBuilder,
    RequestInterface $request,
    FilterBuilder $filterBuilder,
    array $meta = [],
    array $data = []
) {
    $data['config']['filter_url_params']['product_id'] = $request->getParam('cppc_product_id', 0);
    parent::__construct($name, $primaryFieldName, $requestFieldName, $reporting, $searchCriteriaBuilder, $request, $filterBuilder, $meta, $data);
}

You do not need to use any other function. The reason why this is is because it is also updated with an update URL and that does not have that parameter. By using adding that to the data it also parses that into the update url.

You can see that here (Parent function)

/**
 * @return void
 */
protected function prepareUpdateUrl()
{
    if (!isset($this->data['config']['filter_url_params'])) {
        return;
    }
    foreach ($this->data['config']['filter_url_params'] as $paramName => $paramValue) {
        if ('*' == $paramValue) {
            $paramValue = $this->request->getParam($paramName);
        }
        if ($paramValue) {
            $this->data['config']['update_url'] = sprintf(
                '%s%s/%s/',
                $this->data['config']['update_url'],
                $paramName,
                $paramValue
            );
            $this->addFilter(
                $this->filterBuilder->setField($paramName)->setValue($paramValue)->setConditionType('eq')->create()
            );
        }
    }
}