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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)
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