DynamoDb scan not working properly

Question

I am trying to fetch items from the dynamoDb. However when I fetch single item using partiton key everything works fine but when I try to fetch all the items in dynamo db using scan I encouter an error. Following is the code what I am trying to do:

    public List<PageCmsDomain> getAllPages() {
    DynamoDBUtil dynamoDBUtil = new DynamoDBUtil();
    AmazonDynamoDB dynamoDBClient = dynamoDBUtil.getDynamoDBClient();
    DynamoDBMapper mapper = new DynamoDBMapper(dynamoDBClient);
    List<PageCmsDomain> scanResult = mapper.scan(PageCmsDomain.class, new 
    DynamoDBScanExpression());
    return scanResult;

Following error comes when I execute this code:

com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMappingException: PageCmsDomain[restrictions]; could not unconvert attribute
at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapperTableModel.unconvert(DynamoDBMapperTableModel.java:271)
at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper.privateMarshallIntoObject(DynamoDBMapper.java:456)
at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper.marshallIntoObjects(DynamoDBMapper.java:484)
at com.amazonaws.services.dynamodbv2.datamodeling.PaginatedScanList.<init>(PaginatedScanList.java:64)
at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper.scan(DynamoDBMapper.java:1458)
at com.amazonaws.services.dynamodbv2.datamodeling.AbstractDynamoDBMapper.scan(AbstractDynamoDBMapper.java:216)
at com.astro.ott.dynamodb.cmsapi.impl.PageCmsDaoImpl.getAllPages(PageCmsDaoImpl.java:74)
at com.astro.ott.cmsapi.impl.PageCmsGetServiceImpl.getPages(PageCmsGetServiceImpl.java:41)
at com.astro.ott.cms_api.cms_api.PageCmsTestCase.get(PageCmsTestCase.java:81)

Caused by: com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMappingException: not supported; requires @DynamoDBTyped or @DynamoDBTypeConverted
at com.amazonaws.services.dynamodbv2.datamodeling.StandardModelFactories$Rules$NotSupported.get(StandardModelFactories.java:660)
at com.amazonaws.services.dynamodbv2.datamodeling.StandardModelFactories$Rules$NotSupported.get(StandardModelFactories.java:650)
at com.amazonaws.services.dynamodbv2.datamodeling.StandardModelFactories$AbstractRule.unconvert(StandardModelFactories.java:714)
at com.amazonaws.services.dynamodbv2.datamodeling.StandardModelFactories$AbstractRule.unconvert(StandardModelFactories.java:691)
at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBTypeConverter$DelegateConverter.unconvert(DynamoDBTypeConverter.java:109)
at com.amazonaws.services.dynamodbv2.datamodeling.StandardTypeConverters$Vector$ToMap.unconvert(StandardTypeConverters.java:433)
at com.amazonaws.services.dynamodbv2.datamodeling.StandardTypeConverters$Vector$ToMap$1.unconvert(StandardTypeConverters.java:417)
at com.amazonaws.services.dynamodbv2.datamodeling.StandardTypeConverters$Vector$ToMap$1.unconvert(StandardTypeConverters.java:410)
at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBTypeConverter$DelegateConverter.unconvert(DynamoDBTypeConverter.java:109)
at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBTypeConverter$NullSafeConverter.unconvert(DynamoDBTypeConverter.java:128)
at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBTypeConverter$ExtendedConverter.unconvert(DynamoDBTypeConverter.java:88)
at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapperFieldModel.unconvert(DynamoDBMapperFieldModel.java:146)
at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapperFieldModel.unconvertAndSet(DynamoDBMapperFieldModel.java:164)
at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapperTableModel.unconvert(DynamoDBMapperTableModel.java:267)
... 32

And I am using same PageCmsDomain while fetching single item also.

Do you have any attribute called restrictions in class PageCmsDomain? Could you please show the definition of this attribute? Also,Please check whether the data is consistent on this attribute. — notionquest
Yes I do have restrictions attribute.It is defined as follows ' @DynamoDBAttribute(attributeName = "restrictions") private Map<String, Object> restrictions; ' — Pallavi Kaushik

Vasyl Sarzhynskyi Vasyl Sarzhynskyi · Accepted Answer · 2017-10-21T11:08:27

Specified code will work only if restrictions field is null or empty map. Otherwise it will throw exception as DynamoDB does not allow to save or fetch objects that have field with Object type (even as a generic type, in this case - map's value type Object), instead it should have specific type (e.g. String, Integer, Map<String, Integer>).

If restrictions map's value type can't be changed to specific one, you can fix that by adding DynamoDBTypeConvertedJson annotation to store serialized value of restrictions field:

@DynamoDBAttribute(attributeName = "restrictions")
@DynamoDBTypeConvertedJson
private Map<String, Object> restrictions;

Another option is to specify your own custom converter class and annotate restrictions field with @DynamoDBTypeConverted(converter = CustomConverter.class)

DynamoDb scan not working properly

1 Answers