Mapping Java Optional with DynamoDBMapper annotations - amazon-dynamodb

Question

Is there a clean way to map Optional fields with DynamoDBMapper, for both basic types and arbitrary/custom objects?
I believe one option would be to implement DynamoDBTypeConverter for optionals of basic types (Optional<String>, Optional<Integer>, etc). But, in addition to being a bit dirty, this would not work for custom objects.
I am looking for some sort of "chaining" behaviour of converters, where the default converter is applied first and the result wrapped in case of optional fields.
Is there a way to specify this behaviour?
#DynamoDBTable
public class MyModel {
#DynamoDBAttribute
private Optional<String> someStringField;
#DynamoDBAttribute
private Optional<AnotherModel> someAnotherModelField;
...
}
#DynamoDBDocument
public class AnotherModel {
}

Answer 1

For what you want to do, I believe the custom converters is the proper way.
Create a class for example:
class SomeAnotherModelOptionalConverter implements DynamoDBTypeConverter<String, Optional<AnotherModel>> {
#Override
public String convert(Optional<AnotherModel> optional) {
// your conversion from Optional attribute to String DynamoDB attribute
}
#Override
public Optional<AnotherModel> unconvert(String s) {
// your conversion from String DynamoDB attribute to Optional
}
}
Then on your attribute, you add the following tag:
#DynamoDBAttribute
#DynamoDBTypeConverted(converter = SomeAnotherModelOptionalConverter.class)
private Optional<AnotherModel> someAnotherModelField;
Anyways, I would not use an Optional as a field in a class. Instead I would create a getter that has and Optional as a return.
private AnotherModel someAnotherModelField
...
Optional<AnotherModel> getSomeAnotherModelField(){
return Optional.ofNullable(someAnotherModelField);
}
Let me know if that works for you!