Null Response while querying DynamoDB

Question

I am querying dynamodb from lambda function written in node.js env -

Trying to query for table CurrencyPrice where Currency column has value "BLC". When I test my function in lambda console, - it prints until second console log - "querying DB ConsolePrice" and returns a NULL response. It does not print either of the next two console logs and not sure if it is even connecting to DB.

It seems that the code does not go into ddb.query() function at all - had tried putting all loggers in this function but none gets printed.

I have tried checking all possible aws documentation but not able to understand why this function is not getting executed.

My code looks something like below -

var AWS = require ('aws-sdk');
exports.handler = async (event) => 
{ 
  AWS.config.update({region: 'ap-southeast-2'});
  console.log("i am in function");
  // Create DynamoDB service object
  var ddb = new AWS.DynamoDB.DocumentClient();
  var table = 'CurrencyPrice';
  var params = {
    "Select": "ALL_ATTRIBUTES","TableName": "CurrencyPrice",
  };
  console.log("querying DB" + table);
  ddb.query(params, function(err, data) {
    console.log("i am in ddb query");
    if (err) {
      console.error("Unable to query. Error:", JSON.stringify(err, null,2));
    } else {
      console.log(data);   
    }
  });
};

Current result that I am getting in lambda console:

Response:
null
Request ID:"XXXX"
Function Logs:
START RequestId: XXX Version: $LATEST
2019-06-02T13:31:55.189Z    XXXX    INFO    i am in function
2019-06-02T13:31:55.331Z    XXXX    INFO    querying DBCurrencyPrice
2019-06-02T13:31:55.390Z    XXXX    INFO    { Select: 'ALL_ATTRIBUTES', TableName: 'CurrencyPrice' }
END RequestId: XXXX

I expect that at least it prints "Unable to Query" or actual data that it connects to DB and query?

Noel Llevares · Accepted Answer · 2019-06-02 14:41:46Z

2

If you're using async/await you would want to return a promise.

var AWS = require("aws-sdk");
AWS.config.update({ region: "ap-southeast-2" });
var ddb = new AWS.DynamoDB.DocumentClient();

exports.handler = async event => {

  console.log("i am in function");
  // Create DynamoDB service object

  var table = "CurrencyPrice";
  var params = {
    Select: "ALL_ATTRIBUTES",
    TableName: "CurrencyPrice"
  };
  console.log("querying DB" + table);

  return ddb
    .query(params)
    .promise()
    .then((err, data) => {
        console.log("i am in ddb query");
        if (err) {
            console.error("Unable to query. Error:", JSON.stringify(err, null, 2));
        } else {
            console.log(data);
        }
    });
};

answered Jun 2, 2019 at 14:41

Noel Llevares

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Comments

Ranger · Accepted Answer · 2020-08-13 15:11:33Z

1

The AWS example

ddbClient.query(params, callback)

shows a synchronous matter. Execution continues without waiting for the callback finishes. That's why you got Null.

You will have to wrap this .query() call into a Promise, so the execution will wait for completion of this callback.

answered Aug 13, 2020 at 15:11

Ranger

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Comments

Natalie Zhu · Accepted Answer · 2019-12-13 01:08:33Z

0

Make query a promise and wait for its fulfilled state.

const promise = await ddb.query(params, function(err, data) {
   console.log("i am in ddb query");
   if (err) {
    console.error("Unable to query. Error:", JSON.stringify(err, null,2));
   } else {
    console.log(data);
    // process your data   
   }
}).promise();
return promise;

edited Dec 13, 2019 at 1:08

answered Dec 10, 2019 at 23:44

Natalie Zhu

11 bronze badge

1 Comment

Max Over a year ago

Please add an explanation to your code: What does it do, how does it work, and how does it solve OPs problem. Code only answers can lead to cargo cult programming, and you risk getting downvotes.

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