DynamoDB 交易範例

本文為英文版的機器翻譯版本，如內容有任何歧義或不一致之處，概以英文版為準。

本文為英文版的機器翻譯版本，如內容有任何歧義或不一致之處，概以英文版為準。

以 Amazon DynamoDB Transactions 十分實用的情況作為範例，請考慮此線上市場的 Java 應用程式範例。

應用程式在其後端有三個 DynamoDB 資料表：

下訂單

下列程式碼片段說明如何使用 DynamoDB 交易來協調建立和處理訂單所需的多個步驟。使用單一 all-or-nothing操作可確保如果交易的任何部分失敗，交易中不會執行任何動作，也不會進行任何變更。

在此範例中，您可以為 customerId 為 09e8e9c8-ec48 的客戶設定訂單。然後，您可以使用下列簡單的訂單處理工作流程，將其當作單一交易執行：

驗證客戶

首先，請定義一個動作，以便驗證客戶資料表中是否存在 customerId 等於 09e8e9c8-ec48 的客戶。

final String CUSTOMER_TABLE_NAME = "Customers";
final String CUSTOMER_PARTITION_KEY = "CustomerId";
final String customerId = "09e8e9c8-ec48";
final HashMap<String, AttributeValue> customerItemKey = new HashMap<>();
customerItemKey.put(CUSTOMER_PARTITION_KEY, new AttributeValue(customerId));

ConditionCheck checkCustomerValid = new ConditionCheck()
    .withTableName(CUSTOMER_TABLE_NAME)
    .withKey(customerItemKey)
    .withConditionExpression("attribute_exists(" + CUSTOMER_PARTITION_KEY + ")");

更新產品狀態

接下來，如果產品狀態目前是將 IN_STOCK 設定為 true，請定義要將產品狀態更新至 SOLD 的動作。如果項目的產品狀態屬性不等於 IN_STOCK，則設定 ReturnValuesOnConditionCheckFailure 參數會傳回項目。

final String PRODUCT_TABLE_NAME = "ProductCatalog";
final String PRODUCT_PARTITION_KEY = "ProductId";
HashMap<String, AttributeValue> productItemKey = new HashMap<>();
productItemKey.put(PRODUCT_PARTITION_KEY, new AttributeValue(productKey));

Map<String, AttributeValue> expressionAttributeValues = new HashMap<>();
expressionAttributeValues.put(":new_status", new AttributeValue("SOLD"));
expressionAttributeValues.put(":expected_status", new AttributeValue("IN_STOCK"));

Update markItemSold = new Update()
    .withTableName(PRODUCT_TABLE_NAME)
    .withKey(productItemKey)
    .withUpdateExpression("SET ProductStatus = :new_status")
    .withExpressionAttributeValues(expressionAttributeValues)
    .withConditionExpression("ProductStatus = :expected_status")
    .withReturnValuesOnConditionCheckFailure(ReturnValuesOnConditionCheckFailure.ALL_OLD);

建立訂單

最後，只要具有 OrderId 的訂單尚不存在，便可建立訂單。

final String ORDER_PARTITION_KEY = "OrderId";
final String ORDER_TABLE_NAME = "Orders";

HashMap<String, AttributeValue> orderItem = new HashMap<>();
orderItem.put(ORDER_PARTITION_KEY, new AttributeValue(orderId));
orderItem.put(PRODUCT_PARTITION_KEY, new AttributeValue(productKey));
orderItem.put(CUSTOMER_PARTITION_KEY, new AttributeValue(customerId));
orderItem.put("OrderStatus", new AttributeValue("CONFIRMED"));
orderItem.put("OrderTotal", new AttributeValue("100"));

Put createOrder = new Put()
    .withTableName(ORDER_TABLE_NAME)
    .withItem(orderItem)
    .withReturnValuesOnConditionCheckFailure(ReturnValuesOnConditionCheckFailure.ALL_OLD)
    .withConditionExpression("attribute_not_exists(" + ORDER_PARTITION_KEY + ")");

執行交易

下列範例說明如何執行先前定義為單一 all-or-nothing操作的動作。

    Collection<TransactWriteItem> actions = Arrays.asList(
        new TransactWriteItem().withConditionCheck(checkCustomerValid),
        new TransactWriteItem().withUpdate(markItemSold),
        new TransactWriteItem().withPut(createOrder));

    TransactWriteItemsRequest placeOrderTransaction = new TransactWriteItemsRequest()
        .withTransactItems(actions)
        .withReturnConsumedCapacity(ReturnConsumedCapacity.TOTAL);

    // Run the transaction and process the result.
    try {
        client.transactWriteItems(placeOrderTransaction);
        System.out.println("Transaction Successful");

    } catch (ResourceNotFoundException rnf) {
        System.err.println("One of the table involved in the transaction is not found" + rnf.getMessage());
    } catch (InternalServerErrorException ise) {
        System.err.println("Internal Server Error" + ise.getMessage());
    } catch (TransactionCanceledException tce) {
        System.out.println("Transaction Canceled " + tce.getMessage());
    }

讀取訂單詳細資訊

下列範例示範如何以交易方式讀取 Orders 和 ProductCatalog 資料表中的已完成訂單。

HashMap<String, AttributeValue> productItemKey = new HashMap<>();
productItemKey.put(PRODUCT_PARTITION_KEY, new AttributeValue(productKey));

HashMap<String, AttributeValue> orderKey = new HashMap<>();
orderKey.put(ORDER_PARTITION_KEY, new AttributeValue(orderId));

Get readProductSold = new Get()
    .withTableName(PRODUCT_TABLE_NAME)
    .withKey(productItemKey);
Get readCreatedOrder = new Get()
    .withTableName(ORDER_TABLE_NAME)
    .withKey(orderKey);

Collection<TransactGetItem> getActions = Arrays.asList(
    new TransactGetItem().withGet(readProductSold),
    new TransactGetItem().withGet(readCreatedOrder));

TransactGetItemsRequest readCompletedOrder = new TransactGetItemsRequest()
    .withTransactItems(getActions)
    .withReturnConsumedCapacity(ReturnConsumedCapacity.TOTAL);

// Run the transaction and process the result.
try {
    TransactGetItemsResult result = client.transactGetItems(readCompletedOrder);
    System.out.println(result.getResponses());
} catch (ResourceNotFoundException rnf) {
    System.err.println("One of the table involved in the transaction is not found" + rnf.getMessage());
} catch (InternalServerErrorException ise) {
    System.err.println("Internal Server Error" + ise.getMessage());
} catch (TransactionCanceledException tce) {
    System.err.println("Transaction Canceled" + tce.getMessage());
}