REACT-CPP-MONGO

C++ asynchronous mongo library on top of the REACT-CPP library. Uses lambdas and callbacks to return query results.

This library works mostly the same as the regular mongo c++ library, except all functions accept a lambda argument that will be called when results (or failure) are available.

This library is dependent on the mongo C++ driver library (available from their website) as well as the VARIANT-CPP library available at https://github.com/CopernicaMarketingSoftware/VARIANT-CPP

React::Mongo::Connection mongo("mongodb.example.org", [](React::Mongo::Connection *connection, const char *error) {
    // if no error occured, we will receive a null pointer
    if (!error) std::cout << "Connected successfully" << std::endl;

    // otherwise, we will get a description of what exactly went wrong
    else std::cout << "Connection error: " << error << std::endl;
});

/**
 *  The mongo object will be created immediately, even though the connection
 *  might not have been established. It is safe, however, to immediately run
 *  the next command on the object. They will be executed after a connection
 *  was established. Should the library fail to connect, all registered calls
 *  will receive an error.
 */

// build a query to find a specific document
Variant::Value query;
query["_id"] = "documentid";

// retrieve the document
mongo.query("database.collection", std::move(query)).onSuccess([](Variant::Value&& result) {
    // since we search for an exact id, we will get a maximum of one result
    // however, this result will always be an array
    if (result.size() == 0)
    {
        std::cout << "Could not find any document with that ID" << std::endl;
        return;
    }

    // assume that the document has a string field named 'firstname'
    std::string firstname = result[0]["firstname"];
}).onError([](const char *error) {
    std::cout << "Something went wrong querying: " << error << std::endl;
});

Inserting a document is just as easy:

Variant::Value document;
document["name"] = "Example User";
document["email"] = "[email protected]";
document["address"]["city"] = "Gotham City";
document["address"]["phone"] = "555-BATMAN";

mongo.insert("database.collection", std::move(document)).onSuccess([]() {
    std::cout << "Document inserted" << std::endl;
}).onError([](const char *error) {
    std::cout << "Could not insert document: " << error << std::endl;
});

MOVING DATA

You might have noticed that when we pass a document to the library, we have used std::move in all examples so far. While this may not have a big impact in these small examples, working with bigger documents will be noticeably faster using move semantics.

In practice, it is always best to move the object, unless you wish to use the same document again later on. Similarly, all callback functions receiving a document will always receive a movable object. When storing this object, e.g. as a member variable, you should use std::move for this.