rowset.hpp

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// Andrew Naplavkov
 
#ifndef BOAT_DB_ROWSET_HPP
#define BOAT_DB_ROWSET_HPP
 
#include <boat/db/adapted/adapted.hpp>
#include <boost/pfr.hpp>
#include <vector>
 
namespace boat::db {
 
struct rowset {
    std::vector<std::string> columns;
    std::vector<std::vector<variant>> rows;
 
    bool empty() const { return rows.empty(); }
    auto begin() const { return rows.begin(); }
    auto end() const { return rows.end(); }

    variant const& value() const { return rows.at(0).at(0); }
};

template <class T>
constexpr auto view = std::views::transform([](range_of<variant> auto&& r) {
    T ret;
    auto it = std::ranges::begin(r);
    auto vis = [&](auto& v) {
        check(it != std::ranges::end(r), "out of fields");
        read(*it++, v);
    };
    if constexpr (requires { read(*it, ret); })
        vis(ret);
    else
        boost::pfr::for_each_field(ret, vis);
    check(it == std::ranges::end(r), "out of fields");
    return ret;
});

rowset to_rowset(std::ranges::input_range auto&& r)
{
    auto ret = rowset{
        boost::pfr::names_as_array<std::ranges::range_value_t<decltype(r)>>() |
        std::ranges::to<decltype(rowset::columns)>()};
    for (auto&& item : r) {
        auto& row = ret.rows.emplace_back();
        auto vis = [&](auto& v) { write(row.emplace_back(), v); };
        boost::pfr::for_each_field(item, vis);
    }
    return ret;
}
 
}  // namespace boat::db
 
#endif  // BOAT_DB_ROWSET_HPP