protected function _initSelect()
    {
        $request = $this->_objectManager->get('Magento\Framework\App\RequestInterface');
        $this->getSelect()->from(['main_table' => $this->getMainTable()]);

        if(!empty($customerId = $request->getParam('id'))) {
            $this->getSelect()->where('customer_id = ?', $customerId);
        }

        return $this;
    }