Usage of same property as DynamoDBRangeKey and DynamoDBGlobalSecondaryIndexHashKey

[maaaxk]

Greetings to AWS community,

In our project DynamoDb table is configured (cf below) in such a way that one of the properties (e.g. TransactionId) is defined as both

• DynamoDBRangeKey (making part of a composite primary key together with Id)
• GlobalSecondaryIndex (as a HashKey)

The table was successfully created and both Queries (via partition primary key and GSI) are available and working as expected via UI and in our solution written in .NET using AWSSDK.DynamoDBv2.

Meanwhile, in the appropriate DynamoModel described in our code (code below) there is no DynamoDBRangeKey annotation applied to "TransactionId" property, and only DynamoDBGlobalSecondaryIndexHashKey is applied.

So the question is why it is working and allows us to call both methods:

• Task LoadAsync(object hashKey, object rangeKey, CancellationToken cancellationToken = default(CancellationToken)); - using composite primary key
• AsyncSearch QueryAsync(object hashKeyValue, DynamoDBOperationConfig operationConfig = null); - using GSI

DynamoDb Cf

AWSTemplateFormatVersion: '2010-09-09'
Transform: 'AWS::Serverless-2016-10-31'
Description: Dynamo db resources
Parameters: 
  EnvironmentName:
    Type: String
    MinLength: '1'
    AllowedPattern: '[a-zA-Z0-9]*'
Resources:
  OrderTable:
    Type: AWS::DynamoDB::Table
    Properties:
      SSESpecification:
        SSEEnabled: true
      PointInTimeRecoverySpecification:
        PointInTimeRecoveryEnabled: true
      AttributeDefinitions:
        - AttributeName: Id
          AttributeType: S
        - AttributeName: TransactionId
          AttributeType: S
      BillingMode: PAY_PER_REQUEST
      TableName: !Sub ${EnvironmentName}-Order
      KeySchema:
        - AttributeName: Id
          KeyType: HASH
        - AttributeName: TransactionId
          KeyType: RANGE
      GlobalSecondaryIndexes:
        - IndexName: "TransactionIdIndex"
          KeySchema: 
            - AttributeName: "TransactionId"
              KeyType: "HASH"
          Projection: 
            ProjectionType: "ALL"

DynamoDbModel class

    [DynamoDBTable("Order")]
    public class OrderDynamoModel
    {
        [DynamoDBHashKey]
        public string Id { get; set; }
        
        [DynamoDBGlobalSecondaryIndexHashKey("TransactionIdIndex")]
        public string TransactionId { get; set; }
		
        public string ProductCode { get; set; }
		
        public string PaymentStatus { get; set; }

        [DynamoDBVersion]
        public int? VersionNumber { get; set; }
    }

Thank you in advance!

[dscpinheiro]

You didn't share how you created the AmazonDynamoDBClient and DynamoDBContext, but by default the SDK will call the DescribeTable API prior to executing the query in order to:

• Validate the information provided in the attributes
• Fill in missing key or index information

This extra call allows your application to work even if you didn't specify the DynamoDBRangeKey attribute, but it also has a performance impact; see this blog post for more details: https://aws.amazon.com/blogs/developer/improved-dynamodb-initialization-patterns-for-the-aws-sdk-for-net/

[maaaxk]

Thanks a lot @dscpinheiro , this explains why it works!

Can you please also suggest the correct way of describing dynamo db model using "Object Persistence Model" to explicitly mention that "TransactionId" is used as both Composite primary key and GSI?
One of the solutions is to create one more property (e.g. TransactionIdIndex) and apply DynamoDBGlobalSecondaryIndexHashKey attribute against it (since it is not possible to apply 2 attributes "DynamoDBRangeKey" and "DynamoDBGlobalSecondaryIndexHashKey" against the same property) but I'm not sure if this is the optimal way.

Thank you in advance!

[dscpinheiro]

Did you see a specific error when trying to use both attributes? This worked for me for example:

[DynamoDBTable("Order")]
public class OrderDynamoModel
{
    [DynamoDBHashKey]
    public string Id { get; set; }

    [DynamoDBRangeKey, DynamoDBGlobalSecondaryIndexHashKey("TransactionIdIndex")]
    public string TransactionId { get; set; }

    // Other properties
}

---

var ddb = new AmazonDynamoDBClient();
var context = new DynamoDBContext(ddb);

var queryTable = context.QueryAsync<OrderDynamoModel>("1", QueryOperator.LessThan, ["C"]);
var resultTable = await queryTable.GetRemainingAsync();
Console.WriteLine(resultTable.Count);

var queryIndex = context.QueryAsync<OrderDynamoModel>("AAA", new DynamoDBOperationConfig
{
    IndexName = "TransactionIdIndex"
});
var resultIndex = await queryIndex.GetRemainingAsync();
Console.WriteLine(resultIndex.Count);

[maaaxk]

@dscpinheiro this did work out. Thanks a lot!