libbson help to read data into object C++ - c++

Question

i have my unreal project that must read out some BSON document data into a map.
right now i'm able to load that file and print it out with the following code :
void AMyActor::BeginPlay()
{
Super::BeginPlay();
std::ifstream input( filePath , std::ios::binary );
std::vector<unsigned char> buffer(std::istreambuf_iterator<char>(input), {});
bson_t* doc{ bson_new_from_data(buffer.data(),buffer.size()) };
char *str;
if( doc != nullptr )
{
UE_LOG(LogTemp,Warning,TEXT( "Success" ));
str = bson_as_json(doc, NULL);
FString fstr = FString(UTF8_TO_TCHAR(str));
UE_LOG(LogTemp, Warning, TEXT("BSON Output: %s"), *fstr);
}
}
and this is here is where i want to store it :
class Databases
{
std::map<std::string,DatabaseBase> _dictionary;
explicit Databases(const std::map<std::string, DatabaseBase>& dictionary)
: _dictionary(dictionary)
{
}
};
so what i'm looking for is to create a new instance of Databases and initialize "_dictionary" with the content of the bson document.
i'm actually looking for this into the libbson document : http://mongoc.org/libbson/current/bson_t.html
but without success...anyone can help me?
thank's in advance
PS: i'm under unreal but i have linked the libbson library
Update:
since i have to provide how my json file looks like, and DatabaseBase looks like
JSON :
{
"_dictionary" : [ {
"_classID" : "CC00",
"_dictionary" : [ {
"k" : "sample_key",
"v" : ["ACH_00"]
}, {
"k" : "sample_index",
"v" : ["0"]
}]
}, {
"_classID" : "CC01",
"_dictionary" : [ {
"k" : "sample_key",
"v" : ["ACH_01"]
}, {
"k" : "sample_index",
"v" : ["1"]
}]
}]
}
DatabaseBase :
class DatabaseBase
{
public:
DatabaseBase() = default;
std::string sample_key;
int sample_index;
};

Answer 1

Breaking out nlohmann::json:
using nlohmann::json;
std::map<std::string, DatabaseBase> dictionaries;
json input = json::from_bson(buffer);
for (auto& obj : input["_dictionary"]) {
auto name = obj["_classID"];
auto key = obj["_dictionary"][0]["v"][0];
auto idx = stoi(obj["_dictionary"][1]["v"][0].get<std::string>());
auto db = DatabaseBase{key, idx};
dictionaries[name] = db;
}
Databases dbs{dictionaries};
output: (from my debugger)
(lldb) p dbs
(Databases) $0 = {
_dictionary = size=2 {
[0] = {
first = "CC00"
second = (sample_key = "ACH_00", sample_index = 0)
}
[1] = {
first = "CC01"
second = (sample_key = "ACH_01", sample_index = 1)
}
}
}