ItemCollectionMetrics is empty after successful transactWrite using DynamoDB.DocumentClient

Question

I am executing a transactWrite (https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/DynamoDB/DocumentClient.html#transactWrite-property) instruction to DynamoDb and expecting to get back ItemCollectionMetrics (I am specifying ReturnItemCollectionMetrics: 'SIZE' in the request).

The object gets returned empty {} even though changes happened on the dynamo db tables.

Does anyone have an idea about this?

Code

const dynamoResponse = await dynamoDbDocumentClient.transactWrite({
        TransactItems: [
            {
                Put: {
                    TableName: ENV.BLAH_CONTENT_COUNT_MESSAGES_TABLE,
                    ExpressionAttributeNames : {
                        '#v' : 'v',
                    },
                    ExpressionAttributeValues : {
                        ':v' : blah.v
                    },
                    ConditionExpression: '(attribute_exists(blahId) AND #v<>:v) OR attribute_not_exists(blahId)',
                    Item: {...blahCountMessage}
                }
            },
            {
                Update: {
                    TableName: ENV.BLAH_CONTENT_COUNTS_TABLE,
                    Key: { id: blahContentCount.id },
                    ExpressionAttributeNames : {
                        '#v' : 'v',
                        '#count' : 'count',
                        '#contentId': 'contentId'
                    },
                    ExpressionAttributeValues : {
                        ':v' : 1,
                        ':count' : deleted ? -1: 1,
                        ':contentId': blahContentCount.contentId,
                        ':defaultNumber': 0
                    },
                    ConditionExpression: 'attribute_not_exists(cognitoId)',
                    UpdateExpression: 'SET #contentId = :contentId, #count = if_not_exists(#count, :defaultNumber) + :count, #v = if_not_exists(#v, :defaultNumber) + :v',
                    ReturnValuesOnConditionCheckFailure: 'ALL_OLD'
                }
            }
        ],
        ReturnItemCollectionMetrics: 'SIZE'
    }).promise();

Outupt

console.log(JSON.stringify(dynamoResponse.ItemCollectionMetrics)); // {}

Thanks!

Can you change the `ReturnItemCollectionMetrics ` to "NONE" and share the output? — Amit Baranes, Oct 28 '19 at 13:08
I get `undefined` if I do `console.log(JSON.stringify(dynamoResponse.ItemCollectionMetrics));` — Santiago Ferrer Deheza, Oct 28 '19 at 13:38
Well.. this is just a guess but.. Try to remove the `await` `.promise` — Amit Baranes, Oct 28 '19 at 13:41
well, not sure how would that work. the sdk is all base on promises, you need the promise and the wait for the result. — Santiago Ferrer Deheza, Oct 28 '19 at 13:53

Chris Barrett · Accepted Answer · 2019-10-29T19:36:38.813

ReturnItemCollectionMetrics:

"Information about item collections, if any, that were affected by the operation. ItemCollectionMetrics is only returned if the request asked for it. If the table does not have any local secondary indexes, this information is not returned in the response."

Per: https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_ItemCollectionMetrics.html

Could it be that this transaction is either not updating anything - or you don't have an LSI?

Also of note: The documentation says that transactions are disabled for "global tables", I'm not exactly sure if they mean a GSI... but I am not using a LSI which might be also why no ItemCollectionMetrics is ever returned in response to my transactions.

If you update your parameter object to include ReturnConsumedCapacity: 'TOTAL' the response object should look like:

   [ { TableName: 'table_name',
       CapacityUnits: 8,
       WriteCapacityUnits: 8 } ] }

Thanks Chris! Think I missed the `LSI` part on the documentation. Looks like is that! — Santiago Ferrer Deheza, Nov 01 '19 at 11:59

ItemCollectionMetrics is empty after successful transactWrite using DynamoDB.DocumentClient

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