mongodb-atlas-lambda-step1.js

function processEvent(event, context, callback) {
    console.log('Calling MongoDB Atlas from AWS Lambda with event: ' + JSON.stringify(event));
    var jsonContents = JSON.parse(JSON.stringify(event));
    
    //date conversion for grades array
    if(jsonContents.grades != null) {
        for(var i = 0, len=jsonContents.grades.length; i < len; i++) {
            //use the following line if you want to preserve the original dates
            //jsonContents.grades[i].date = new Date(jsonContents.grades[i].date);
            
            //the following line assigns the current date so we can more easily differentiate between similar records
            jsonContents.grades[i].date = new Date();
        }
    }
    
    //the following line is critical for performance reasons to allow re-use of database connections across calls to this Lambda function and avoid closing the database connection. The first call to this lambda function takes about 5 seconds to complete, while subsequent, close calls will only take a few hundred milliseconds.
    context.callbackWaitsForEmptyEventLoop = false;
    
    try {
        if (cachedDb == null) {
            console.log('=> connecting to database');
            MongoClient.connect(atlas_connection_uri, function (err, client) {
                cachedDb = client.db('travel');
                return createDoc(cachedDb, jsonContents, callback);
            });
        }
        else {
            createDoc(cachedDb, jsonContents, callback);
        }
    }
    catch (err) {
        console.error('an error occurred', err);
    }
}

function createDoc (db, json, callback) {
  db.collection('restaurants').insertOne( json, function(err, result) {
      if(err!=null) {
          console.error("an error occurred in createDoc", err);
          callback(null, JSON.stringify(err));
      }
      else {
        console.log("Kudos! You just created an entry into the restaurants collection with id: " + result.insertedId);
        callback(null, "SUCCESS");
      }
      //we don't need to close the connection thanks to context.callbackWaitsForEmptyEventLoop = false (above)
      //this will let our function re-use the connection on the next called (if it can re-use the same Lambda container)
      //db.close();
  });
};