DynamoDB + Store Values as Items or JSON

Question

New to DynamoDB.

I'm creating a table with Primary Key 'UserID', Composite Key 'DateTime' and then I have the following as a value (note: I don't need to query any specifics in the below data - just write and read it):

UserID1
UserID2
Message
DateTime

Questions:

1. is there any advantage in storing these 4 values as separate items or as one JSON string?
2. UserID1 and Datetime in the stored value also make up the Primary/Composite Key - am I right assuming there is no point in storing these in the data/value as I can access this from the returned Keys when quering?

Answer 1

So your options are:

Hash Key | Range Key  | Attributes
----------------------------------
user id  | utc time   | json data
----------------------------------
user123  | 1357306017 | {UserID1:0, UserID2:0, Message:"", DateTime:0}

or

Hash Key | Range Key  | Attributes
--------------------------------------------------------------
user id  | utc time   | UserID1 | UserID2 | Message | DateTime
--------------------------------------------------------------
user123  | 1357306017 | 0       | 0       | ""      | 0

Both are viable options, and the choice comes down to how you want to read the data, if you have an attribute for each item, then you can request those attributes individually.

We tend to use a hybrid approach based upon our usage patterns. Elements we need to access individually are given their own attributes. Elements that we only ever want to access along with a collection of other elements all get assigned a single attribute and are then stored as a single blob of JSON string or a base64 encoded data.

For part two, indeed, you are right, you don't need to store user id and date time again as part of the attributes because they are the hash and range keys, which are returned when you make a request.

Answer 2

With DynamoMapper you could do this in Java:

@DynamoDBTable(tableName = "myClass")
public class MyClass {

    @DynamoDBHashKey(attributeName = "id")
    private String id;

    @DynamoDBRangeKey(attributeName = "rangeKey")
    private long rangeKey;

    @DynamoDBTypeConvertedJson
    private Content content;

}

And the content class could be:

public class Content {

    @JsonProperty
    private List<Integer> integers = new ArrayList();

    @JsonProperty
    private List<String> strings = new ArrayList();

}

Answer 3

DynamoDB now supports json object direct storing. read: http://aws.amazon.com/blogs/aws/dynamodb-update-json-and-more/