Unrecognized method 'isLoaded()' in Magento 2

Question

I'm trying to join product and my custom table but it's returning error

Unrecognized method 'isLoaded()'

my code is:

 /**
 * @param \Magento\Backend\Block\Template\Context $context
 * @param \Magento\Backend\Helper\Data $backendHelper
 * @param \Learning\Helloworld\Model\ResourceModel\Subscriber\CollectionFactory $collectionFactory
 * @param \Learning\Helloworld\Model\Status $status
 * @param \Magento\Framework\App\ResourceConnection $resource
 * @param \Psr\Log\LoggerInterface $loggerInterface
 * @param ProductFactory $productFactory
 * @param array $data
 */
public function __construct(
    \Magento\Backend\Block\Template\Context $context,
    \Magento\Backend\Helper\Data $backendHelper,
    \Learning\Helloworld\Model\ResourceModel\Subscriber\CollectionFactory $collectionFactory,
    \Learning\Helloworld\Model\Status $status,
    \Magento\Framework\App\ResourceConnection $resource,
    \Psr\Log\LoggerInterface $loggerInterface,
    \Magento\Catalog\Model\ProductFactory $productFactory,
    array $data = []
) {
    $this->_status = $status;
    $this->_collectionFactory = $collectionFactory;
    $this->_productFactory = $productFactory;
    $this->_resource = $resource;
    $this->_log = $loggerInterface;
    parent::__construct($context, $backendHelper, $data);
}

/**
     * Prepare grid collection object
     *
     * @return $this
     */
    protected function _prepareCollection()
    {
        $collection = $this->_collectionFactory->create();         

        $productCollection =  $this->_productFactory->create()->getCollection();
        $select = $productCollection->getSelect();
        $tempCollection = $collection->getSelect();

        $temp =  $tempCollection->join(
            array('product' => $this->_resource->getTableName('catalog_product_entity')),
            'main_table.product_id = product.entity_id'
         );

        $this->_log->debug((string)$temp);

        $this->setCollection($temp);

        return parent::_prepareCollection();
    }

When I debug the sql query it's returning

SELECT `main_table`.*, `product`.* FROM `custom_info` AS `main_table`
 INNER JOIN `catalog_product_entity` AS `product` ON main_table.product_id = product.entity_id

and it's returning result also but still i'm getting isLoaded() Error?

Could you please let me know if my query wrong?

Answer 1

Remove '$temp = ' and $this->setCollection($tempCollection);, So code look like

/**
     * Prepare grid collection object
     *
     * @return $this
     */
    protected function _prepareCollection()
    {
        $collection = $this->_collectionFactory->create();         

        $productCollection =  $this->_productFactory->create()->getCollection();
        $select = $productCollection->getSelect();
        $tempCollection = $collection->getSelect();

        $tempCollection->join(
            array('product' => $this->_resource->getTableName('catalog_product_entity')),
            'main_table.product_id = product.entity_id'
         );

        $this->setCollection(tempCollection);

        return parent::_prepareCollection();
    }