mongodb-atlas-lambda-step1.js

function processEvent(event, context, callback) {
    const storableEvent = makeEventStorable(event);
    storableEvent.created_at = new Date();
    console.log('Calling MongoDB Atlas from AWS Lambda: ', JSON.stringify(storableEvent));

    if (cachedDb) {
        console.log('- Reusing cached connection');
        createDoc(cachedDb, storableEvent, callback);
        return;
    }

    console.log('- Connecting to database');
    MongoClient.connect(atlasConnectionUri, (err, db) => {
        if (err) {
            console.error('... Error: ', err);
            callback(err);
            return;
        }
        console.log('... Done');
        cachedDb = db;
        createDoc(cachedDb, storableEvent, callback);
    });
}

function makeEventStorable(event) {
    const data = {};
    Object.keys(event).forEach((key) => {
        if (key !== 'grades') {
            data[key] = event[key];
            return;
        }
        data[key] = event[key].map((grade) => {
            grade.date = new Date(grade.date);  // use real JS dates
            return grade;
        });
    });
    return data;
}

function createDoc(db, data, done) {
    console.log('- Creating document');
    db.collection('restaurants')
        .insertOne(data, (err, result) => {
            if (err) {
                console.error('... Error: ', err);
                return done(err);
            }

            console.log("... Done", result.insertedId);
            done(null);  // done() should work, but it doesn't in lambda-local (not in master)
        });
};