Java DynamoDBMapper. Mapping Attribute value 'M'

Question

I'm just getting started on my first DynamoDB project and I've been trying to read the documentation as much as possible. I think the best possibility for my project is to use the High Level DynamoDbMapper in the SDK to allow CRUD operations.

In the DynamoDB Documentation there is a type of attribute value 'M' which can be seen here http://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_AttributeValue.html

In the lower level java API, such as getItem, or getItemBatch, this value type translates to java.util.map<>.

But I can't seem to find any resources that say I can use the HigherLevel DBMapper to use this data type. Supported Data Types here. http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/DynamoDBMapper.DataTypes.html

I noticed at the bottom of the page it gives some insight to creating your own higher level mapping system. But I figured I would ask here first before I dove into the code for trying that. So I guess my question is... Is there anyway to use the DynamoDBMapper to work with a Java.Util.Map data type?

The only insight I could find on google was this weird github error where the user is seemingly doing exactly what I want to do. https://github.com/aws/aws-sdk-java/issues/520

Hope this makes sense. Ralph

Answer 1

UPDATE: Noticed that you need map a Java.Util.Map property into DynamoDB map attribute, so everything below doesn't answer your question, sorry. In my case, a property of custom class is used, not a property of Java.Util.Map class.

---

Suppose your table has name "my_table", and suppose the following is a json dump of a record:

{
  uuid: "52f9d257-7998-4379-928b-9d41d70dd8a8",
  my_map: {
    field1: 123,
    field2: 456
  }  
}

(Here my_map is the desired field of 'M' type)

To use DynamoDBMapper for such table you would need to create two annotated classes, the first one for the table itself:

import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBAttribute;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBHashKey;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBTable;

@DynamoDBTable(tableName="my_table")
public class MyClass {
    private String uuid;
    private MyMapClass myMap; 

    @DynamoDBHashKey(attributeName="uuid")
    public String getUuid() {
        return uuid;
    }   
    public void setUuid(String uuid) {
        this.uuid = uuid;
    }

    @DynamoDBAttribute(attributeName = "my_map")    
    public MyMapClass getMyMap() {
        return myMap;
    }
    public void setMyMap(MyMapClass myMap) {
        this.myMap = myMap;
    }       
}

and the second one -- for the my_map field:

import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBAttribute;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBDocument;


@DynamoDBDocument
public class MyMapClass {
    private int field1;
    private int field2;

    @DynamoDBAttribute(attributeName = "field1")    
    public int getField1() {
        return field1;
    }
    public void setField1(int field1) {
        this.field1 = field1;
    }

    @DynamoDBAttribute(attributeName = "field2")    
    public int getField2() {
        return field2;
    }
    public void setField2(int field2) {
        this.field2 = field2;
    }
}

Here is a usage example:

...
DynamoDBMapper dbMapper = new DynamoDBMapper(dbClient);
...
MyClass item = new MyClass();
item.setUuid("52f9d257-7998-4379-928b-9d41d70dd8a8");
MyMapClass map = new MyMapClass();
map.setField1(123);
map.setField2(456);
item.setMyMap(map);
dbMapper.save(item);

Hope this helps!