DynamoDB 事务示例 - Amazon DynamoDB
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DynamoDB 事务示例

作为 Amazon DynamoDB Transactions 可能有用的情况示例,请考虑此适用于在线商城的 Java 应用程序示例。

该应用程序在后端有三个 DynamoDB 表:

  • Customers— 此表存储有关商城买家的详细信息。它的主键是 CustomerId 唯一标识符。

  • ProductCatalog— 此表存储有关商品在商城中销售的价格和供货情况等详细信息。它的主键是 ProductId 唯一标识符。

  • Orders— 此表存储有关来自市场的订单的详细信息。它的主键是 OrderId 唯一标识符。

下订单

以下代码片段说明了如何使用 DynamoDB 事务来协调创建和处理订单所需的多个步骤。使用单个全有或全无操作可确保如果事务的任何部分失败,事务中不会运行任何操作,也不会进行任何更改。

在此示例中,您设置来自 customerId09e8e9c8-ec48 的客户订单。然后,您可以使用以下简单的订单处理工作流将其作为单个事务处理运行:

  1. 确定客户 ID 是否有效。

  2. 确保产品是 IN_STOCK,并将产品状态更新为 SOLD

  3. 确保订单不存在,然后创建订单。

验证客户

首先,定义一个操作以验证 customerId 等于 09e8e9c8-ec48 的客户存在于客户表中。

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 + ")");

更新产品状态

接下来,定义一个操作,如果产品状态当前设置为 IN_STOCK 的条件为 true,则将产品状态更新为 SOLD。设置 ReturnValuesOnConditionCheckFailure 参数,如果项目的产品状态属性不等于 IN_STOCK,则返回项目。

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);

创建订单

最后,只要不存在具有 OrderId 的订单,则创建订单。

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 + ")");

运行事务

以下示例说明如何运行以前定义为单个全有或全无操作的操作。

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()); }

阅读订单详细信息

以下示例演示了如何以事务方式读取 OrdersProductCatalog 表中已完成的订单。

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()); }

其他示例