Once from_json and to_json functions overloading appeared in the lib it became easy to build and serialize custom classes from and to json. But it can be more easy if lib provide ability to create a map for each type with json keys strings and member pointers as values.
For example right now one have to write a code like this
Regions.h
#include <string>
#include <vector>
#include <json/json.hpp>
#include "City.hpp"
namespace DataModel {
struct Region {
std::string name;
std::vector<City> cities;
};
using nlohmann::json;
void to_json(json &j, const Region &o);
void from_json(const json &j, Region &o);
}Region.cpp
#include "Region.hpp"
namespace Keys {
const std::string name = "name";
const std::string cities = "cities";
}
void DataModel::to_json(json &j, const Region &o) {
using namespace Keys;
j = {
{ name, o.name },
{ cities, o.cities },
};
}
void DataModel::from_json(const json &j, Region &o) {
using namespace Keys;
o.name = j[name];
o.cities = j[cities].get<decltype(o.cities)>();
}Now keys are stored in datamodel class implementation file. It's ok but it can be implemented even shorter and more comfortable if lib could store an std::map<std::string, F T::*> for T class (Region in the example above). Of course one cannot create such a map in C++ cause value may have different types. But this kind of mapping can be implemented with variadic templates just like sqlite_orm works (look at make_column function). To implement this functionality developer can create template specialization like this:
Region.hpp
#include <string>
#include <vector>
#include <json/json.hpp>
#include "City.hpp"
namespace DataModel {
struct Region {
std::string name;
std::vector<City> cities;
};
using nlohmann::json;
template<>
struct key_value_mapper<Region> {
auto operator()() const {
return make_mapper(make_mapping("name", &Region::name), make_mapping("cities", &Region::cities));
}
};
}City is omitted in the example but it also has from_json and to_json overriden and has the only field std::string name.
Once
from_jsonandto_jsonfunctions overloading appeared in the lib it became easy to build and serialize custom classes from and to json. But it can be more easy if lib provide ability to create a map for each type with json keys strings and member pointers as values.For example right now one have to write a code like this
Regions.hRegion.cppNow keys are stored in datamodel class implementation file. It's ok but it can be implemented even shorter and more comfortable if lib could store an
std::map<std::string, F T::*>for T class (Regionin the example above). Of course one cannot create such a map in C++ cause value may have different types. But this kind of mapping can be implemented with variadic templates just like sqlite_orm works (look atmake_columnfunction). To implement this functionality developer can create template specialization like this:Region.hppCityis omitted in the example but it also hasfrom_jsonandto_jsonoverriden and has the only fieldstd::string name.