How to do a basic sort in DynamoDb?

Simply, this can't be achieved in DynamoDB if the due attribute is not defined as sort key. Even if you define the due attribute as sort key, the ordering can be done only within the particular partition key. The ordering can't be done across the partition key.

Assume, you have defined the due as sort key of the table. You can use ScanIndexForward to true/false to order the items in ascending / descending order.

Data modeling in dynamo db involves designing the partition key and then determining the sort key for a use case. Partition key is compulsory for any query. This is a basic design premise of a key value nosql store which is completely different than a relational store