documentClient with LSI returns LastEvaluatedKey for last record

[jatinmehrotra]

Confirm by changing [ ] to [x] below to ensure that it's a bug:

• I've gone through Developer Guide and API reference
• I've checked AWS Forums and StackOverflow for answers
• I've searched for previous similar issues and didn't find any solution
• This is an issue with version 2.x of the SDK

Describe the bug
I am trying pagination with LSI, my table has 3 LSI. Upon reaching the last record it should not return LastevaluatedKey, however it returns LastEvaluatedKey which makes it difficult to paginate backward.
Other 2 LSI index are working fine and keeps LastEvaluatedKey as null for last records

If on Node.js, are you running this on AWS Lambda?
yes i am running on AWS Lambda

Details of the browser/Node.js version
v16.1.0

SDK version number
v2.970.0
To Reproduce (observed behavior)

params.ScanIndexForward = false;
  response = await dynamoDb.query(paramsForQuery).promise();
  console.log('response', response);
  const arrayLength = response.Items.length;
  LastEvalSortKey = {
    pk: userId,
    originalUrl: response.Items[0].originalUrl,
  };
  if (sortBy === 'createdAt')
    LastEvalSortKey[sortBy] = response.Items[0].createdAt;
  if (sortBy === 'updatedAt')
    LastEvalSortKey[sortBy] = response.Items[0].updatedAt;
  if (sortBy === 'convertedUrl')
    LastEvalSortKey[sortBy] = response.Items[0].convertedUrl;
  return {
    items: response.Items,
    nextToken: arrayLength
      ? Base64.encodeURI(JSON.stringify(LastEvalSortKey))
      : prevToken,
    prevToken: response.LastEvaluatedKey
      ? Base64.encodeURI(JSON.stringify(response.LastEvaluatedKey))
      : undefined,
  };

Expected behavior
response.LastEvaluatedKey should be null for last record which is not, how to determine last record for reverse pagination.

[vudh1]

Hi @jatinmehrotra thanks for reaching out. According to this documentation, LastEvaluatedKey being empty means that there is no more data to be retrieved, but if it is not empty, it does not necessarily mean that there is more data. A way you can try to workaround is to query for page + 1 items, then check how many items the query return would help to paginate backward.