Mongodb c++ regex query - c++

Question

How to query MongoDB database using regex in c++.
mongo-cxx-driver-r3.1.1
hear is include
#include <cstdlib>
#include <iostream>
#include <bsoncxx/builder/stream/document.hpp>
#include <bsoncxx/json.hpp>
#include <mongocxx/client.hpp>
#include <mongocxx/instance.hpp>
#include <mongocxx/uri.hpp>
#include <cstdint>
#include <vector>
#include <mongocxx/stdx.hpp>
#include <bson.h>
#include <conio.h>
#include <sstream>
#include <stdio.h>
#include <string>
#include <bsoncxx/types.hpp>
#include <mongocxx/exception/exception.hpp>
#include <bsoncxx/builder/basic/document.hpp>
#include <bsoncxx/builder/basic/kvp.hpp>
using bsoncxx::builder::stream::close_document;
using bsoncxx::builder::stream::document;
using bsoncxx::builder::stream::finalize;
using bsoncxx::builder::stream::open_document;
using bsoncxx::builder::basic::kvp;
using bsoncxx::builder::basic::make_document;
here is what I have tried.
void MyClass::on_querybtn_clicked()
{
auto collection = conn["TestDB"]["fdevices"];
bsoncxx::types::b_regex::b_regex();//i am lost here dont know how to use it
auto cursor = collection.find({});
for (auto doc : cursor) {
QString qstr = QString::fromStdString(bsoncxx::to_json(doc));
QJsonDocument docum = QJsonDocument::fromJson(qstr.toUtf8());
QJsonObject object = docum.object();
QString call = object["Data"].toString();
ui.mqttList->addItem(call);
}
}
Previously I build a software using Java now I am trying to build same software in Qt c++, I am new to c++.
Here is query code that I used in java for Query.
DBObject query = new BasicDBObject();
Pattern regex = Pattern.compile("^14-09-2017");
query.put("Data", regex);
here is how my data look like.
Database image

Answer 1

Use some builders and make the document, providing the string input for the pattern:
#include <bsoncxx/builder/basic/document.hpp>
#include <bsoncxx/builder/basic/kvp.hpp>
using bsoncxx::builder::basic::kvp;
using bsoncxx::builder::basic::make_document;
auto cursor = collection.find(make_document(
kvp("Data", bsoncxx::types::b_regex{"^14-09-2017"})
));
A bit easier to read than stream builder IMHO, but the basic premise is there. Still a string for input, much like Pattern.compile()

Answer 2

I've tried several approaches but finally I came up with the most straightforward one. I build a query as a json and then convert is to bson using bsoncxx::from_json function.
a working piece of code looks like:
mongocxx::instance instance{};
mongocxx::uri uri("mongodb://localhost:27017");
mongocxx::client *m_c = new mongocxx::client(uri);
std::string query = "{\"name.firstName\": {\"$options\": \"i\",\"$regex\": \"^pattern\"}}";
bsoncxx::builder::stream::document doc;
//this one to define q not inside try catch block.
bsoncxx::document::value q(doc.view());
try{
q = bsoncxx::from_json(query);
}catch (bsoncxx::exception &e){
std::cerr<<"error: "<<e.code()<<" "<<e.what();
return;
}
mongocxx::options::find opt;
mongocxx::cursor cursor = m_c->database("db_name").collection("collection_name").find( std::move(q), opt);
An important thing here is that I could not use q as bsoncxx::document::view.
Because a value for this view is created inside try - catch block, till the time
when the control flow came to the find function bsoncxx::document::view q was always empty. So I had to use bsoncxx::document::value q and move semantics in the find function.

Answer 3

#include <bsoncxx/builder/basic/document.hpp>
#include <bsoncxx/builder/basic/kvp.hpp>
using bsoncxx::builder::basic::kvp;
using bsoncxx::builder::basic::make_document;
auto cursor = collection.find(make_document(kvp("field",make_document(kvp("$regex":"pattern"),kvp("$options","i"))));
Refer To Official