Null Response while querying DynamoDB - amazon-web-services

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?

Answer 1

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);
}
});
};

Answer 2

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.

Answer 3

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;