Poco::ODBC with Complex Data Types

[xakod]

I looked through POCO ODBC User Guide, tryeid some things and after all i have no idea how to (de-)serialize Complex Data Types if one or more struct members can be optional (i need to know column is null or zero for example).
Example:

class Person
{
public:
    // default constructor+destr.
    // getter and setter methods for all members
    // ...

private:
    std::string _firstName;
    std::string _lastName;
    Poco::UInt64 _socialSecNr;
    std::optional<Poco::DateTime> _dateBirth
};

namespace Poco {
namespace Data {

template <>
class TypeHandler<class Person>
{
public:
    static void bind(std::size_t pos, const Person& obj, AbstractBinder::Ptr pBinder, AbstractBinder::Direction dir)
    {
        poco_assert_dbg (!pBinder.isNull());
        // the table is defined as Person (FirstName VARCHAR(30), lastName VARCHAR, SocialSecNr INTEGER(3))
        // Note that we advance pos by the number of columns the datatype uses! For string/int this is one.
        TypeHandler<std::string>::bind(pos++, obj.getFirstName(), pBinder, dir);
        TypeHandler<std::string>::bind(pos++, obj.getLastName(), pBinder, dir);
        TypeHandler<Poco::UInt64>::bind(pos++, obj.getSocialSecNr(), pBinder, dir);
        // what should be here for _dateBirth?
    }

    static std::size_t size()
    {
        return 4; // we handle four columns of the Table!
    }

    static void prepare(std::size_t pos, const Person& obj, AbstractPreparator::Ptr pPrepare)
    {
        poco_assert_dbg (!pPrepare.isNull());
        // the table is defined as Person (FirstName VARCHAR(30), lastName VARCHAR, SocialSecNr INTEGER(3))
        // Note that we advance pos by the number of columns the datatype uses! For string/int this is one.
        TypeHandler<std::string>::prepare(pos++, obj.getFirstName(), pPrepare);
        TypeHandler<std::string>::prepare(pos++, obj.getLastName(), pPrepare);
        TypeHandler<Poco::UInt64>::prepare(pos++, obj.getSocialSecNr(), pPrepare);
        // what should be here for _dateBirth?
    }

    static void extract(std::size_t pos, Person& obj, const Person& defVal, AbstractExtractor::Ptr pExt)
        /// obj will contain the result, defVal contains values we should use when one column is NULL
    {
        poco_assert_dbg (!pExt.isNull());
        std::string firstName;
        std::string lastName;
        Poco::UInt64 socialSecNr = 0;
        TypeHandler<std::string>::extract(pos++, firstName, defVal.getFirstName(), pExt);
        TypeHandler<std::string>::extract(pos++, lastName, defVal.getLastName(), pExt);
        TypeHandler<Poco::UInt64>::extract(pos++, socialSecNr, defVal.getSocialSecNr(), pExt);
         // what should be here for _dateBirth?
        obj.setFirstName(firstName);
        obj.setLastName(lastName);
        obj.setSocialSecNr(socialSecNr);
    }

private:
    TypeHandler();
    ~TypeHandler();
    TypeHandler(const TypeHandler&);
    TypeHandler& operator=(const TypeHandler&);
};

} } // namespace Poco::Data

Of course, I can use RecordSet and I use it. But I don't want to have reallocs.

[xakod]

Same question https://stackoverflow.com/questions/68636510/how-to-read-values-possibly-null-from-database-into-stdvector-via-pocodata but no anwser also