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dgrr/pgxx_variadic_select.cc

CreatedSeptember 26, 2022 14:13

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pgxx_variadic_select.cc

	#include<iostream>
	#include<pqxx/pqxx>
	#include<string>
	#include<string>

	template<size_t I,classIt,classT,classTuple>
	std::enable_if_t<(I == std::tuple_size<Tuple>::value -1)>assign(It it, It end, T& v, Tuple& tp)
	{
	if (it == end)
	return;
	v = it->templateas<T>();
	}

	template<size_t I,classIt,classT,classTuple>
	std::enable_if_t<(I < std::tuple_size<Tuple>::value -1)>assign(It it, It end, T& v, Tuple& tp)
	{
	if (it == end)
	return;
	v = it->templateas<T>();
	assign<I+1>(++it, end, std::get<I+1>(tp), tp);
	}

	template<classQuery,class... Types>
	voidexec(std::string conn_str, Query query, std::vector<std::tuple<Types...>>& vs)
	{
	pqxx::connectionC(conn_str);
	pqxx::nontransactionN(C);
	auto r = N.exec(query);

	vs.resize(r.size());

	for (constauto& row : r)
	{
	auto& tp = vs[row.rownumber()];
	assign<0>(row.begin(), row.end(), std::get<0>(tp), tp);
	}
	}

	template<classQuery,class... Types>
	voidexec(std::string conn_str, Query query, std::tuple<Types...>& tp)
	{
	pqxx::connectionC(conn_str);
	pqxx::nontransactionN(C);
	auto r = N.exec(query);

	for (constauto& row : r)
	{
	assign<0>(row.begin(), row.end(), std::get<0>(tp), tp);
	}
	}

	template<classQuery,classT>
	voidexec(std::string conn_str, Query query, T& v)
	{
	pqxx::connectionC(conn_str);
	pqxx::nontransactionN(C);
	auto r = N.exec(query);

	for (constauto& row : r)
	{
	if (row.size() >0)
	{
	v = row[0].templateas<T>();
	break;
	}
	}

	C.disconnect();
	}

	intmain()
	{
	constchar *conn_str ="host=localhost port=8812 user=admin password=quest dbname=qdb";
	std::vector<std::tuple<std::string,int,double>> vs;

	exec(conn_str,"SELECT DISTINCT coin, trades FROM market", vs);
	for (auto& v : vs)
	std::cout << std::get<0>(v) <<" \|" << std::get<1>(v) << std::endl;

	int x;
	exec(conn_str,"SELECT count() from market", x);
	std::cout <<"count() =" << x << std::endl;
	}

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dgrr/pgxx_variadic_select.cc