DynamoDBMappingException on mapping Map<String, Object>attribute

Question

I am trying to save the instance of the class bellow into dynamdb but getting DynamoDBMappingException: not supported; requires @DynamoDBTyped or @DynamoDBTypeConverted exception.

@DynamoDBTable(tableName = "FulfillmentOrders")
public class FulfillmentOrder {

    @DynamoDBHashKey
    private String orderId;

    @DynamoDBAttribute
    @DynamoDBTyped(value = DynamoDBMapperFieldModel.DynamoDBAttributeType.M)
    private Map<String, Object> body;

    ....... 
}

It fails during map conversion, seems the problem is in Object generic type.

could someone help, where is the problem here or maybe SDK doesn't support such kind of conversion ?

Thanks!

biniam · Accepted Answer · 2018-11-01 11:12:01Z

4

DynamoDB won't know how to convert the objects in the Map<,>, you'll have to create a custom type converter. once you've done this you can annotate the prooperty with @DynamoDBTypeConverted(converter = xxx):

In your example:

@DynamoDBTable(tableName = "FulfillmentOrders")
public class FulfillmentOrder {

    @DynamoDBHashKey
    private String orderId;

    @DynamoDBAttribute
    @DynamoDBTypeConverted(converter = BodyTypeConverter.class)
    private Map<String, Object> body;
}


static public class BodyTypeConverter implements DynamoDBTypeConverter<String, Map<String, Object>> {

    @Override
    public String convert(Map<String, Object> object) {
        DimensionType itemDimensions = (Map<String, Object>) object;

        // Convert the object to a DynamoDB json string
        String json = "wibble";

        return json;
    }

    @Override
    public DimensionType unconvert(String s) {
        Map<String, Object> item = new Map<String, Object>();

        // Convert s to a Map<String, Object> here.

        return item;
    }
}

More information can be found here

edited Nov 1, 2018 at 11:12

biniam

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answered Jul 12, 2018 at 8:38

Kevin Smith

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6 Comments

Aram Mkrtchyan Over a year ago

Thanks for the reply Kevin! So from your answer it means that the body attribute in DynamoDb should of String type instead of Map right ? In my case it's Map type.

Kevin Smith Over a year ago

String is just one of many types that DynamoDB supports, as long as you map in to a supported type you'll be fine (Here's a list of supported types docs.aws.amazon.com/amazondynamodb/latest/developerguide/…)

Aram Mkrtchyan Over a year ago

In the case when body attribute will have String type, this solution works fine. But if the type is Map (document) a conversion fails.It seems that if I want to have a document type I should have mirroring POJO, Map<String, Object> will not work in that case.

Kevin Smith Over a year ago

That's because it doesn't know how to map Object to a DynamoDB type. Thus you have to tell it how to map your Object

Aram Mkrtchyan Over a year ago

Yes, that's the point. Values of the map can be have any DynamoDB supported type. Do you have some example for this case? Thank you Kevin!

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