Node.JS Lambda Function Not Returning JSON

Question

I'm new to NodeJS, and JS in general (mostly a PHP and C# guy), so I could really use some help with this function below.

The goal is to receive a JSON payload, connect to MySQL, and then return the results of the query in a JSON response. I've got it connecting to the DB, I can read the JSON data that it receives (event.fieldname) but for some reason it's not sending back the JSON for the applicant_data variable.

Do I just have the variable in the wrong location? When I run the code below I just get back "{}" as the returned data.

Thanks in advance for the help!

NodeJS Code:

exports.handler = function(event, context, callback) {
console.log('Starting:');
console.log("Request received:\n", JSON.stringify(event));

var mysql = require('mysql');



var jsonconnection = mysql.createConnection({
    host: 'servername',
    user: 'username',
    password: 'password',
    database: 'database'
 });

jsonconnection.connect();
console.log('Connected to MySQL:');

jsonconnection.query('SELECT applicant_id FROM customers WHERE applicant_id = \'' + event.applicant_id + '\'',
    function(err,res){
    if(err) throw err;

    console.log('Row Details:', JSON.stringify(res));
        var applicant_data = {
            applicant_id : res.applicant_id
        };

    jsonconnection.end();

    context.succeed(applicant_data);
 })
};

How are you invoking the Lambda function? Via API gateway? Or directly via the AWS SDK? — Mark B
– Mark B, Commented Aug 17, 2016 at 13:05
Please add the output of line console.log('Row Details:', JSON.stringify(res)); — John Siu
– John Siu, Commented Aug 17, 2016 at 15:29
Results from console.log('Row Details:') Row Details: [{"applicant_id":"WQFV7CWXA39E9TXT"}] — Josh
– Josh, Commented Aug 17, 2016 at 15:36

John Siu · Accepted Answer · 2016-08-17 16:53:08Z

4

I am not familiar with AWS, but base on http://docs.aws.amazon.com/lambda/latest/dg/nodejs-prog-model-handler.html, following code may work.

exports.handler = function (event, context, callback) {
    console.log('Starting:');
    console.log("Request received:\n", JSON.stringify(event));

    var mysql = require('mysql');

    var jsonconnection = mysql.createConnection({
        host: 'servername',
        user: 'username',
        password: 'password',
        database: 'database'
    });

    // Move applicant_data outside of query as it will be needed at the end in callback
    var applicant_data = {};

    jsonconnection.connect();
    console.log('Connected to MySQL:');

    jsonconnection.query('SELECT applicant_id FROM customers WHERE applicant_id = \'' + event.applicant_id + '\'',
        function (err, res) {
            if (err) throw err;

            console.log('Row Details:', JSON.stringify(res));
            applicant_data = {
                // Only use first row of data
                applicant_id: res[0].applicant_id;
            };

        });

    // Move connection end out side of query
    jsonconnection.end();

    // This should return your data, in JSON form
    callback(null, JSON.stringify(applicant_data));

    // I assume this is the correct use for succeed
    context.succeed();
};

edited Aug 17, 2016 at 16:53

answered Aug 17, 2016 at 15:54

John Siu

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7 Comments

Josh Over a year ago

Hi @john-siu, Unfortunately that doesn't work as expected... I tried that earlier :-) What it sends back is the following with the brackets before and after... not exactly JSON :-( [ { "applicant_id":"WQFV7CWXA39E9TXT" } ]

Josh Over a year ago

If I return the applicant_data JSON variable outside of the callback function it returns the data as I would expect without the brackets.

John Siu Over a year ago

@Josh It is JSON, but wrapped in an array. The data is in first item of the array.

John Siu Over a year ago

@Josh Try without JSON.stringify in callback, it is not required. I updated my answer. docs.aws.amazon.com/lambda/latest/dg/…

Josh Over a year ago

Thanks for the assist here... I tried it without the stringify and I'm still getting just a { } :-(

|

Oded Breiner · Accepted Answer · 2020-06-28 07:01:19Z

3

exports.handler = async (event) => {
    let jsonResponse = {"hello":"world"}
    const response = {
        statusCode: 200,
        body: JSON.stringify(jsonResponse),
    };
    return response;
};

answered Jun 28, 2020 at 7:01

Oded Breiner

29.9k10 gold badges110 silver badges74 bronze badges

2 Comments

Crashalot Over a year ago

Is it possible to return the JSON data as an object instead of a string?

Oded Breiner Over a year ago

@Crashalot this would be interpreted as an object by most clients and servers.

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