DynamoDB: How can I create a table with nested JSON structure?

Question

I want to create a table in dynamoDB with below structure.

{
  "CartId": 123,
  "UserId": 356,
  "CartItems": [
    {
      "ProductId": 100,
      "Quantity": 50
    },
    {
      "ProductId": 121,
      "Quantity": 51
    }
  ]
}

Everywhere in tutorials and documents it says that we can only have below type of attributes in the table:

Set of Strings
Set of Numbers
Set of Binary

I can't think of a way to store above structure in DynamoDB. Could you please help out?

I am using object mapper Api of java. It would be great if you can also tell me how can I create a class which can be mapped to this particular table structure.

score 23 · Answer 1 · edited Feb 11 '20 at 03:49

23

Simplest way is use @DynamoDBDocument

Add Maven dependency

<dependency>
        <groupId>com.amazonaws</groupId>
        <artifactId>aws-java-sdk-dynamodb</artifactId>
        <version>1.11.186</version>
</dependency>

Create POJO

@DynamoDBTable(tableName = "Customer")
public class Customer
{ 
    @DynamoDBHashKey
    @DynamoDBAutoGeneratedKey
    private String id;

    private String firstName;

    private List<Foo> fooList;
}

@DynamoDBDocument
public static class Foo {
    private String name;
}

Create a repository

@EnableScan
public interface CustomerRepository extends CrudRepository<Customer,String>

Then call customerRepository.save(customer). The result will be like this:

{
  "firstName": "Test",
  "fooList": [
    {
      "name": "foo"
    },
    {
      "name": "foo2"
    }
  ],
  "id": "e57dd681-8608-4712-a39a-f3e0f31a5e27"
}

edited Feb 11 '20 at 03:49

alessiosavi

2,753
2
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answered Sep 03 '17 at 07:21

sendon1982

9,982
61
44

Hi, when we use this solution, what happens if we add new fields to the inner class, will they be present in dynamo db? – Bhargav Dec 07 '17 at 09:10
Yes, it is going to be there – sendon1982 Dec 08 '17 at 03:45
How to map generic json in pojo using @DynamoDBDocument..like i have key,value pair with different value object. – Ruchi Jul 08 '21 at 10:23

score 4 · Answer 2 · edited Feb 11 '20 at 02:03

Posting to an old question because I did not think the solution was easy to find. Hope this helps someone.

Step 1: Create a complex Java object that mirrors the structure desired.

List<HashMap<String, Integer>> cartItems = new ArrayList<HashMap<String, Integer>>();
HashMap<String, Integer> item1 = new HashMap<String, Integer>();
item1.put("ProductId", 100);
item1.put("Quantity", 50);
cartItems.add(item1);
HashMap<String, Integer> item2 = new HashMap<String, Integer>();
item2.put("ProductId", 121);
item2.put("Quantity", 51);
cartItems.add(item2);

Step 2: Update DynamoDB item with the complex object.

I use a helper method:

private void updateAttribute(int id, String newAttribute, Object newValue){
    Map<String, Object> newValues = new HashMap<String, Object>();
    newValues.put(":value", newValue);

    UpdateItemSpec updateItemSpec = new UpdateItemSpec()
            .withPrimaryKey("id", id)
            .withUpdateExpression("set " + newAttribute + " = :value")
            .withValueMap(newValues);

    siteTable.updateItem(updateItemSpec);
}

and then call thus:

updateAttribute(123, "CartItems", cartItems);

The newly added cart items attribute displays in DynamoDB like:

{
 "CartItems": [
   {
     "ProductId": 100,
     "Quantity": 50
   },
   {
     "ProductId": 121,
     "Quantity": 51
   }
 ]
}

I have not tested an upsert scenario. In the past, upsert functionality did not seem to be present: https://forums.aws.amazon.com/thread.jspa?threadID=162907

Regarding reads of deeply nested items: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.AccessingItemAttributes.html#DocumentPaths

score 4 · Answer 3 · answered Jan 04 '20 at 07:03

Bit Late to the party but would like to share this. I was able to store a deep nested Json Doc by defining the column attribute as below in my Java Entity.

@DynamoDBAttribute
@DynamoDBTypeConvertedJson
private List<Map<String,Object>> pageData;

Input Json:

 {
    "userId": 359628,
    "platform": "learn-web",
    "inactive_duration": 0,
    "total_time": 15,
    "device_type": "web",
    "page_data": [{
        "page_details": {
            "page_type": "segmentView",
            "time": 15,
            "segment_id": 65590,
            "session_id": 13140,
            "module_id": 4363
        },
        "items": [{
            "type": "component",
            "id": 267307,
            "sub_type": "video",
            "time": 10,
            "metadata": {
                "lastPlaybackRate": 1,
                "currentTime": 0,
                "isLocked": false,
                "video": {
                    "videoType": "BRIGHTCOVE",
                    "viewingTime": 156,
                    "videoSize": 7120441,
                    "url": "5378655747001",
                    "URL": "5378655747001"
                }
            }
        }]
    }]
}

As stored in Dynamo DB-Snap

@DynamoDBAttribute - this is not applicable to fields... have you tried this before ? — Arundev, Jun 13 '22 at 16:39

score 1 · Answer 4 · answered Sep 30 '14 at 12:31

1

You can store JSONs in Dynamodb as Strings. It all depends on what you want to do with the data and how to retrieve it.

The DynamoDB Java API for instance, introduces Marshaller objects that transforms any Java object into a String so you can store it and fetch it automagically from a DynamoDB attribute.

answered Sep 30 '14 at 12:31

Chen Harel

9,684
5
44
58

How can we achieve this? – Amit Oct 01 '14 at 00:05
You said DynamoDB wants sets of strings, but it can also save strings. Which SDK/programming language are you using? – Chen Harel Oct 01 '14 at 06:12
i have json file with nested objects, i'm trying to import it in my table created in aws dynamo, i'm running `aws dynamodb put-item` but failed to import data, any help? – Prathamesh Doke Jan 20 '20 at 11:51

score 1 · Answer 5 · answered Oct 03 '20 at 17:29

If you have the JSON in a string, you can simply call

table.putItem(Item.fromJSON(jsonString));

The JSON needs to contain keys/values for the partition and sort key. For a conditional put, use

table.putItem(Item.fromJSON(jsonString), conditionString, nameMap, valueMap)

score 0 · Answer 6 · answered Dec 05 '16 at 01:46

Not sure if these data types were available when this question was asked (there is a good chance that they were not) but these days you'd use the List datatype for the CartItems and each cart item would be of Map datatype.

Reference: DynamoDB Data Types

score 0 · Answer 7 · answered Oct 23 '22 at 09:44

The following is the annotated way of doing it in V2 (Equivalent of @DynamoDBDocument). For more information check their GitHub Issue Page.

@DynamoDbBean
public class Cart {

    private String cartId;
    private String userId;
    
    private List<CartItem> cartItems;
}

@DynamoDbBean
public class CartItem {

    private String productId;
    private Integer quantity;
}

DynamoDB: How can I create a table with nested JSON structure?

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