dynamodb.put().promise() not returning the put object

Question

I am trying to make use of the async/await functionality with regard to aws and dynamo db. Below is an example of how to put an object pre asyn await, as you can see in the callback you have access to data which contains the put object. However in the second block of code which uses async and promise the result is an empty object, any thoughts?

https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/GettingStarted.NodeJs.03.html

Non Promise Version

var docClient = new AWS.DynamoDB.DocumentClient();

var table = "Movies";

var year = 2015;
var title = "The Big New Movie";

var params = {
    TableName:table,
    Item:{
        "year": year,
        "title": title,
        "info":{
            "plot": "Nothing happens at all.",
            "rating": 0
        }
    }
};

console.log("Adding a new item...");
docClient.put(params, function(err, data) {
    if (err) {
        console.error("Unable to add item. Error JSON:", JSON.stringify(err, null, 2));
    } else {
        console.log("Added item:", JSON.stringify(data, null, 2));
    }
});

Promise async Version - assume the wrapping function is marked async

var docClient = new AWS.DynamoDB.DocumentClient();

var table = "Movies";

var year = 2015;
var title = "The Big New Movie";

var params = {
    TableName:table,
    Item:{
        "year": year,
        "title": title,
        "info":{
            "plot": "Nothing happens at all.",
            "rating": 0
        }
    }
};
const result: any = await dynamoDb.put(params).promise()
console.log(result) 

Solution 1

According to the doc you have to use ReturnValues if you want something back.

Solution 2

When you're using promises, you should handle the returned promise object using .then() and .catch(). If you take a look at the documentation, your request should look like this:

dynamoDb.put(params).promise()
  .then(function(data) {
    console.log(data);
  })
  .catch(function(err) {
    console.log(err);
  });

This will also help you see if you are getting any error (same idea as surrounding an await with try/catch, but clearer syntax)

Solution 3

I have tried ReturnValues: 'ALL_OLD' but in async await it has no result.

Here is a part of code:

const answersParams = {
          TableName: ANSWERS_TABLE,
          Item: {
            answersId,
            answers,
            userId,
            quizId,
          },
          ReturnValues: 'ALL_OLD',
        };

        try {
          const createdAnswres = await db.put(answersParams).promise();

          return {
            statusCode: 201,
            body: JSON.stringify(createdAnswres && createdAnswres.Item),
          };
        } catch (error) {
          return {
            statusCode: 500,
            body: 'failed to save user answers',
          };
        }
      }
    

So I had to add another request to db:

const createdAnswres = await db.get({
              TableName: ANSWERS_TABLE,
              Key: { answersId },
            })
            .promise();
    

Comments

[Gabriel Bleu]

What is : any ?

[Mingo]

its typescript, just means that result can be of any type

[Gabriel Bleu]

Maybe you should update the tags

[Gabriel Bleu]

Are you catching the errors ?

[Mingo]

There are no errors, Database updates successfully just the response object is empty

[akauppi]

You likely mean docClient.put in the async example, instead of dynamoDb.put? If so, would you please fix the typo

[Costa Michailidis]

db.put() returns and empty {} object by default.

[Mingo]

presumably clearer syntax is a matter of opinion and shouldn't affect the behavior? No error is being thrown, the object is being created in the database but the response is an empty object rather than the put object

[Deiv]

Yupe shouldn't affect behavior, but handling the promise success/error in the correct way is not an opinion. It's successful and the object returned is empty, even when using .then()? That can't be possible...

[Mingo]

According to this aws.amazon.com/blogs/compute/… both methods are "corret" ways of handling promise success and error. Anyway i tried it using .then().catch() and behaviour is the same, empty response object, weird

[Mingo]

hmm yes that does seem to make sense, weird how the non promise object does seem to return the full object in the callback regardless of whether you have set this value, TBH i dont really need a response but it bugged me the behavior appeared different and wanted to make sure I wasnt missing anything / doing anything silly. Thanks for looking into it, ill mark this as the correct answer

[K-Sid]

I found that you can also use docClient.update even when creating a new item. ReturnValues can then accept a value of ALL_NEW which will return what you are looking for. In the case of docClient.put you can't use the ALL_NEW option for ReturnValues. Hopefully this helps anyone else that stumbles across this.