code: protected function initConnection()
      {
          $this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
          if ($this->emulatePrepare !== null && constant('PDO::ATTR_EMULATE_PREPARES')) {
              $this->pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, $this->emulatePrepare);
          }
          if ($this->charset !== null && in_array($this->getDriverName(), ['pgsql', 'mysql', 'mysqli', 'cubrid'], true)) {
              $this->pdo->exec('SET NAMES ' . $this->pdo->quote($this->charset));
          }
          $this->trigger(self::EVENT_AFTER_OPEN);
      }
docs: Initializes the DB connection.
  This method is invoked right after the DB connection is established.
  The default implementation turns on `PDO::ATTR_EMULATE_PREPARES`
  if [[emulatePrepare]] is true, and sets the database [[charset]] if it is not empty.
  It then triggers an [[EVENT_AFTER_OPEN]] event.