yii\db\Connection::initConnection PHP Method

    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);
    }

 /**
  * 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.
  */
 protected function initConnection()
 {
     parent::initConnection();
     if ($this->defaultSchema) {
         $this->pdo->exec('SET CURRENT SCHEMA ' . $this->pdo->quote($this->defaultSchema));
     }
     if ($this->isISeries === null) {
         try {
             $stmt = $this->pdo->query('SELECT * FROM QSYS2.SYSTABLES FETCH FIRST 1 ROW ONLY');
             $this->isISeries = boolval($stmt);
         } catch (\Exception $ex) {
             $this->isISeries = false;
         }
     }
 }