def METHOD_NAME(self, validated_data):
    codes = set()
    seats = set()
    errs = []
    err = False
    for voucher_data in validated_data:
        if voucher_data.get('seat') and (voucher_data.get('seat'), voucher_data.get('subevent')) in seats:
            err = True
            errs.append({'code': ['Duplicate seat ID in request.']})
            continue
        else:
            seats.add((voucher_data.get('seat'), voucher_data.get('subevent')))
        if voucher_data['code'] in codes:
            err = True
            errs.append({'code': ['Duplicate voucher code in request.']})
        else:
            codes.add(voucher_data['code'])
            errs.append({})
    if err:
        raise ValidationError(errs)
    return super().METHOD_NAME(validated_data)