Starting from approximately 07:58, the secondary index examples imply that choosing an attribute in a nested object as a key of the index is possible, which is not true for DynamoDB. According to this document (https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/SecondaryIndexes.html):
The key schema for the index. Every attribute in the index key schema must be a top-level attribute of type String, Number, or Binary. Other data types, including documents and sets, are not allowed.
My experiments with DynamoDB also aligned with this behavior that the document describes.
If I’m not missing anything here, please kindly update the lecture to avoid confusion for other audience.