Getting just number of rows for query

[pdobrev]

Is there any way to obtain only the number of rows using DataMapper.query?

The documentation for DynamoDB suggests using the Select query option (https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_Query.html#DDB-Query-request-Select), but it does not seem to be available in the QueryOptions interface.

Should one use the aws-sdk API for such functionality, or is it somehow available using DataMapper (or if not, is it planned)?

Thanks!

[jeskew]

At the moment that is not supported, but there's no reason it couldn't be. You can get the count today from the iterators returned by mapper.query and mapper.scan, though the iterators will be unmarshalling all fetched items during the iteration.

Getting the results of a query and getting just its result count use the same amount of read capacity, but using Select: COUNT in the initial request would save network bandwidth and a bit of processing.

[pdobrev]

Thanks for the explanation! I did not realize that it consumes the same amount of read capacity.

For time being, I implemented that particular functionality using the aws-sdk and selecting only COUNT.

[kennu]

I'm also missing a simple way to count all the items returned by a query or a scan, for purposes of pagination and showing the total count to the user.

As I understand, the underlying library has to make multiple requests with lastEvaluatedKey to get all the items for counting, while with Select: COUNT you only need one request to get the count.

[franz101]

#Metoo

[jdvachhani95]

#Metoo