golang, scan nullable sql columns

scan_nullable_sql_columns.go

func Scan(rows *sql.Rows, dest ...interface{}) error {
	proxy := make([]interface{}, len(dest))

	for k, v := range dest {
		switch v.(type) {
		case *string:
			proxy[k] = &sql.NullString{String: "", Valid: true}
		case *bool:
			proxy[k] = &sql.NullBool{Bool: false, Valid: true}
		case *int:
			proxy[k] = &sql.NullInt32{Int32: 0, Valid: true}
		case *int32:
			proxy[k] = &sql.NullInt32{Int32: 0, Valid: true}
		case *int64:
			proxy[k] = &sql.NullInt64{Int64: 0, Valid: true}
		case *float32:
			return errors.New("unable to map float32. use float64 instead")
		case *float64:
			proxy[k] = &sql.NullFloat64{Float64: 0, Valid: true}
		case *time.Time:
			proxy[k] = &sql.NullTime{Time: time.Time{}, Valid: true}
		default:
			return errors.New("unable to map. unknown field type")
		}
	}
	if err := rows.Scan(proxy...); err != nil {
		return err
	}
	for k, v := range dest {
		switch d := v.(type) {
		case *string:
			*d = (proxy[k].(*sql.NullString)).String
		case *bool:
			*d = (proxy[k].(*sql.NullBool)).Bool
		case *int:
			*d = int((proxy[k].(*sql.NullInt32)).Int32)
		case *int32:
			*d = (proxy[k].(*sql.NullInt32)).Int32
		case *int64:
			*d = (proxy[k].(*sql.NullInt64)).Int64
		case *float64:
			*d = (proxy[k].(*sql.NullFloat64)).Float64
		case *time.Time:
			*d = (proxy[k].(*sql.NullTime)).Time
		}
	}
	return nil
}