code: protected function _initDbResource()
      {
          $registry = $this->getPluginResource('db');
          if (!$registry) {
              return;
          }
  
          //
          // options in configs/application
          $options = $registry->getOptions();
  
          if (array_key_exists('dsn', $options) && '' !== $options['dsn']) {
              $options['params'] = array_replace(
                  $options['params'],
                  $this->_parseDsn($options['dsn'])
              );
          }
  
          $registry->setOptions($options);
      }
docs: Initialize the database resource.