Daniel

• want to subtract 8 from balance, before that we should check balance is greater than 8.

        DynamoDbClient ddb = DynamoDbClient.builder().region(Region.of("us-east-1"))
  				.credentialsProvider(ProfileCredentialsProvider.create("cats")).build();
  
  		HashMap<String, AttributeValue> itemKey = new HashMap<>();
  		itemKey.put("pk", AttributeValue.builder().s("1_1234").build());
  		itemKey.put("sk", AttributeValue.builder().s("FME").build());
  
  		Map<String, String> expressionAttributesNames = new HashMap<>();
  		expressionAttributesNames.put("#kn0", "balance");
  		Map<String, AttributeValue> expressionAttributeValues = new HashMap<>();
  		expressionAttributeValues.put(":kv0", AttributeValue.builder().n("8").build());
  
  		UpdateItemRequest updateItemRequest = UpdateItemRequest.builder().tableName("future_match_engine-uat")
  				.key(itemKey).updateExpression("SET #kn0 = #kn0 - :kv0").conditionExpression("balance > :kv0")
  				.expressionAttributeNames(expressionAttributesNames)
  				.expressionAttributeValues(expressionAttributeValues).returnValues(ReturnValue.UPDATED_NEW).build();
  
  		try {
  			UpdateItemResponse updateItemResponse = ddb.updateItem(updateItemRequest);
  			System.out.println(updateItemResponse);
  		} catch (ConditionalCheckFailedException e) {
  			System.out.println("fail.");
  		}