[adev-code]

Motivation and Context

Fixes #2265.

Customer wanted to save a List of their own objects inside an item as a list of maps, not flattened. The DynamoDB Enhanced Client README only shows flattening ("Flat map attributes from another class"), so they couldn't find how to do it. The two working approaches from the issue thread weren't documented in the README.

Modifications

• services-custom/dynamodb-enhanced/README.md: new section "Store a list of objects inside an item", placed before "Flat map attributes from another class". It shows:
  • how the item is stored (a DynamoDB list of maps),
  • the annotations approach (@DynamoDbBean on both classes, TableSchema.fromBean(...)),
  • the StaticTableSchema approach (EnhancedType.listOf(EnhancedType.documentOf(...))),
  • that addAttribute(List.class, ...) fails with IndexOutOfBoundsException, the error from the issue,
  • a link to "Save complex types" in the AWS SDK for Java 2.x Developer Guide.

No code changes.

Testing

Documentation-only change. The code in the new section was run exactly as written:

• Real DynamoDB, us-east-1, AWS SDK for Java 2.56.0, Java 17:
  • Annotations approach: the item is saved as recordMetadata = L:[ M:{id, details}, M:{id, details} ] and reads back correctly.
  • StaticTableSchema approach: same stored item, reads back correctly.
  • addAttribute(List.class, ...): building the schema fails with java.lang.IndexOutOfBoundsException: Index: 0 (DefaultAttributeConverterProvider.findConverter reads the list element type with rawClassParameters().get(0), and a raw List.class has none).
• Both snippets compile with javac -Xlint:all with no warnings. To compile, each class was put in its own file with a package line, and the two static schema fields were put inside a class.
• Not tested: query/scan/update on these items, @DynamoDbImmutable classes, other SDK versions.

https://github.com/adev-code/aws-sdk-java-v2/blob/gh-2265-readme-list-of-objects/services-custom/dynamodb-enhanced/README.md#store-a-list-of-objects-inside-an-item

License

• I confirm that this pull request can be released under the Apache 2 license