DynamoDB Dynomite Querying Scan Index Forward
You can use scan_index_forward and scan_index_backward to change the ordering of the results. Examples:
Product.where(category: "Electronics", sku: 101).scan_index_forward.first
Product.where(category: "Electronics", sku: 101).scan_index_forward(false).first
Product.where(category: "Electronics", sku: 101).scan_index_backward.first
Product.where(category: "Electronics").scan_index_backward.first
The Primary Key needs to have Sort Key for scan_index_forward to work. This is the way DynamoDB works.
Faster Last Method
Dynomite provides a last method that returns the last item of a table, IE: Product.last. Unfortunately, to generalize it, it must do a scan operation and iterates through all the pages. This can be slow for large tables.
If you can scope the query by the Partition Key and Sort Key, it’s more efficient to use scan_index_backward.first to grab the last item. The query operation will be used, and the “last” item is the “first” item. So we don’t even have to paginate through all the pages and make multiple API calls for large result sets.