Unable to increment score in dynamodb table using DynamoDB document client - Javascript

Question

I have a working serverless application deployed on Lambda (nodejs6.10) and can create and read users from my DynamoDB, however, I have been having problems trying to perform an update on a specific attribute.

Basically, my table has a key of userId and two attributes called email and score.

The application detects if a referral code (userId) was supplied and if so it should increment their score by 1. Below are the params that I am passing to the dynamoDb.update function.

if (refcode) {
      console.log("A referral code: " + refcode + " was detected");

      const params = {
        TableName: USERS_TABLE,
        Key: {
          userId: refcode
        },
        UpdateExpression: "set score = score + :val",
        ExpressionAttributeValues: {
          ":val": 1
        },
        ReturnValues: "UPDATED_NEW"
      };

      console.log(params);

      dynamoDb.update(params, (error, result) => {
        console.log("Checking for error...");
        if (error) {
          console.log(error);
          res.status(400), json({ error: "Could not GET user" });
        }
        console.log("Checking for result...");
        if (result.Item) {
          console.log("Item updated");
          const { userId, email, score } = result.Item;
        } else {
          res.status(404).json({ error: "Invalid referral code" });
          console.log("Invalid ref code");
        }
      });
    }

In Cloudwatch I can see that my function has entered this part of the logic successfully, however, it looks like it never runs the dynamoDb.update part. Here are the cloudwatch logs:

START RequestId: 7d92d4da-a710-11e8-abdd-039e23e278bd Version: $LATEST
2018-08-23T20:09:52.392Z    7d92d4da-a710-11e8-abdd-039e23e278bd    A referral code: cEBeGM1sk was detected
2018-08-23T20:09:52.393Z    7d92d4da-a710-11e8-abdd-039e23e278bd    { TableName: '**<redacted>**',
Key: { userId: 'cEBeGM1sk' },
UpdateExpression: 'set score = score + :val',
ExpressionAttributeValues: { ':val': 1 },
ReturnValues: 'UPDATED_NEW' }
2018-08-23T20:09:52.550Z    7d92d4da-a710-11e8-abdd-039e23e278bd    Reached the end - taking user to thank you page
END RequestId: 7d92d4da-a710-11e8-abdd-039e23e278bd
REPORT RequestId: 7d92d4da-a710-11e8-abdd-039e23e278bd  Duration: 1530.76 ms    Billed Duration: 1600 ms Memory Size: 128 MB    Max Memory Used: 45 MB  

Any help much appreciated! It should work according to the atomic update example given on the AWS documentation: AWS Documentation

Answer 1

Use add not set. If initial value is undefined, 0 will be used.

This code does what is expected to be done:

const AWS = require('aws-sdk');
const getEnv = require('../../../helpers/environment/get');

AWS.config.update({
  accessKeyId: getEnv('AWS_ACCESS_KEY'),
  secretAccessKey: getEnv('AWS_ACCESS_KEY_SECRET'),
  region: getEnv('AWS_REGION'),
});

const client = new AWS.DynamoDB.DocumentClient();

const queryResult = await dynamo.update({
    TableName: getEnv('AWS_DYNAMO_TABLE_LOG'),
    Key: {
      pk: 'a',  
      t: 1,  
    },
    UpdateExpression: 'add #test :value',
    ExpressionAttributeNames: {
      '#test': 'test_incr',
    },
    ExpressionAttributeValues: {
      ':value': 2,
    },
    ReturnConsumedCapacity: 'TOTAL',
    ReturnValues: 'ALL_NEW',
  }, (error, data) => {console.log({error, data})});

Consider using a newer version of NodeJS with your lambda ;) any was supported recent LTS is often best choice https://github.com/nodejs/Release#release-schedule

Also for DynamoDB nodejs client i personaly find this doc most usefull: https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/DynamoDB/DocumentClient.html

P.s. about lambda version, at the moment supported versions are node 14 and 12 without additional config. Yet some of aws services when integrating requires older version, aka 12