DynamoDb HashKey Attribute name

Question

Is there any way to get the attribute name of HashKey of a dynamodb table in java?

e.g., if the dyanmodb table schema is 
(
 "HashKey, String", SSNId
 "SortKey, Long", Pincode
 "String", Name 
)
So I should be able to get the output like this:-
getHashKeyAttributeName(String tableName) --> SSNId
getSortkeyAttributeName(String tableName) --> Pincode
getOtherAttributeList(String tableName) --> Name

prayagupa prayagupa · Accepted Answer · 2017-06-24T03:10:26

you simply need to iterate on the keySchemas and attributeDefinitions when you the describe the table.

DynamodbTable description has following structure, (I'm using clojure-aws, you can use aws cli to see the table structure)

user=> (db/describe-table {:profile "aws-profile" :endpoint "us-west-2"} "KeyValueLookupTable1")
{:table {:key-schema [{:key-type "HASH", :attribute-name "leaseKey"}], :table-size-bytes 201, :attribute-definitions [{:attribute-name "leaseKey", :attribute-type "S"}], :creation-date-time #object[org.joda.time.DateTime 0x4c6ece3 "2017-06-07T15:50:35.057-07:00"], :item-count 1, :table-status "ACTIVE", :table-name "KeyValueLookupTable1", :provisioned-throughput {:read-capacity-units 10, :write-capacity-units 10, :number-of-decreases-today 0}, :table-arn "arn:aws:dynamodb:us-west-2:033814027302:table/KeyValueLookupTable1"}}

where you can see key-schema and attribute-definitions keys which you will need to iterate on.

1) See the documentation for TableDescription#getKeySchema to get the HASH and RANGE keys.

example with java8

  DynamoDB dynamoDB = new DynamoDB(new AmazonDynamoDBClient())

  String getHashKeyAttributeName(String tableName) {

    TableDescription tableSchema = dynamoDB.getTable(tableName).describe();

    return tableSchema.getKeySchema().stream()
            .filter(x -> x.getKeyType().equals(KeyType.HASH.toString()))
            .findFirst().get().getAttributeName();        
  }

  String getSortkeyAttributeName(String tableName) {

    TableDescription tableSchema = dynamoDB.getTable(tableName).describe();

    return tableSchema.getKeySchema().stream()
            .filter(x -> x.getKeyType().equals(KeyType.RANGE.toString()))
            .findFirst().get().getAttributeName();
  }

2) For other fields, you need to iterate on List<AttributeDefinitions> which you get on tableDescription.getAttributeDefinitions

List<String> getOtherAttributeList(String tableName) {

    DynamoDB dynamoDB = new DynamoDB(new AmazonDynamoDBClient());
    TableDescription tableSchema = dynamoDB.getTable(tableName).describe();

    return tableSchema.getAttributeDefinitions().stream()
            .map(AttributeDefinition::getAttributeName)
            .collect(Collectors.toList());
}

DynamoDb HashKey Attribute name

1 Answers