如何使用SOCI从数据库中获取整行？

Question

... and save it into self-defined object type? I'm using PostgreSQL. When I have everything in one file, it works. But I wanted to split this into class-files like you always do when writing in cpp. When I divided my code into *.h and *.cpp files, I'm getting errors.

Here are my files:

test.h

class MyInt
{
public:
    MyInt();
    MyInt(int i);

    void set(int i);
    int get() const;

private:
    int i_;
};

test.cpp

#include "test.h"
#include <soci.h>
#include <postgresql/soci-postgresql.h>

MyInt::MyInt()
{

}

MyInt::MyInt(int i)
{
    this->i_ = i;
}

int MyInt::get() const
{
    return this->i_;
}

void MyInt::set(int i)
{
    this->i_ - i;
}

namespace soci
{
    template <>
    struct type_conversion<MyInt>
    {
        typedef int base_type;

        static void from_base(int i,  soci::indicator ind, MyInt & mi)
        {
            if (ind ==  soci::i_null)
            {
                throw soci_error("Null value not allowed for this type");
            }

            mi.set(i);
        }

        static void to_base(const MyInt & mi, int & i,  soci::indicator & ind)
        {
            i = mi.get();
            ind = soci::i_ok;
        }
    };
}

main.cpp

#include <iostream>
#include "test.h"

int main(int argc, char **argv)
{

    MyInt i;
    sql.open(soci::postgresql, "dbname=mydb user=postgres password=postgrespass");
    sql << "SELECT count(*) FROM person;", soci::into(i);
    std::cout << "We have " << i.get() << " persons in the database.\n";
    sql.close();

    return 0;
}

I compile it like this:

g++ main_test.cpp test.h test.cpp -o App -lsoci_core -lsoci_postgresql -ldl -lpq -I /usr/local/include/soci -I /usr/include/postgresql

and got those errors:

In file included from /usr/local/include/soci/into-type.h:13:0,
                 from /usr/local/include/soci/blob-exchange.h:12,
                 from /usr/local/include/soci/soci.h:18,
                 from main_test.cpp:3:
/usr/local/include/soci/exchange-traits.h: In instantiation of â€soci::details::exchange_traits<MyInt>’:
/usr/local/include/soci/into.h:29:60:   instantiated from â€soci::details::into_type_ptr soci::into(T&) [with T = MyInt, soci::details::into_type_ptr = soci::details::type_ptr<soci::details::into_type_base>]’
main_test.cpp:29:59:   instantiated from here
/usr/local/include/soci/exchange-traits.h:35:5: error: incomplete type â€soci::details::exchange_traits<MyInt>’ used in nested name specifier

THE ABOVE PROBLEM IS SOLVED, TAKE A LOOK AT @JohnBandela ANSWER.

Answer 1

The code where you specialize type_conversion

template<>
struct type_conversion<MyInt>

Needs to be in test.h not test.cpp. The problem is if you have it in test.cpp like you do now, it is not visible in main.cpp where you are using SOCI