var tmp User
	err = tx.Session(&gorm.Session{}).First(&tmp, user.ID).Error
	if err != gorm.ErrInvalidDB {
		t.Fatalf("must got a gorm.ErrInvalidDB while execution after db close, got %+v instead", err)
	}

	// must be error
	if lastErr != gorm.ErrInvalidDB && !isUsingClosedConnError(lastErr) {
		t.Fatalf("exp error gorm.ErrInvalidDB, got %+v instead", lastErr)
	}
	if lastRunIndex >= loopCount || lastRunIndex < closeStartIdx {

	// ErrEmptySlice empty slice found
	ErrEmptySlice = errors.New("empty slice found")
	// ErrDryRunModeUnsupported dry run mode unsupported
	ErrDryRunModeUnsupported = errors.New("dry run mode unsupported")
	// ErrInvalidDB invalid db
	ErrInvalidDB = errors.New("invalid db")
	// ErrInvalidValue invalid value
	ErrInvalidValue = errors.New("invalid value, should be pointer to struct or slice")
	// ErrInvalidValueOfLength invalid values do not match length

	if sqldb, ok := db.ConnPool.(*sql.DB); ok {
		return sqldb, nil
	}

	if dbConnector, ok := db.ConnPool.(GetDBConnector); ok && dbConnector != nil {
		return dbConnector.GetDBConn()
	}

	return nil, ErrInvalidDB
}

func (db *PreparedStmtDB) Close() {
	db.Mux.Lock()
	defer db.Mux.Unlock()

	for _, stmt := range db.Stmts {
		go func(s *Stmt) {
			// make sure the stmt must finish preparation first
			<-s.prepared

		if sqldb, err := dbConnector.GetDBConn(); sqldb != nil || err != nil {
			return sqldb, err
		}
	}

	if sqldb, ok := connPool.(*sql.DB); ok && sqldb != nil {
		return sqldb, nil
	}

	return nil, ErrInvalidDB
}

func (db *DB) getInstance() *DB {
	if db.clone > 0 {
		tx := &DB{Config: db.Config, Error: db.Error}

		if db.clone == 1 {
			// clone with new statement
			tx.Statement = &Statement{