DynamoDB-如何检索和删除（弹出）项目？ [英] DynamoDB - how to retrieve and delete (pop) an item?

问题描述

我正在开发用Flask编写的应用程序，该应用程序通过boto访问由Amazon的DynamoDB支持。

I am working on an application written in Flask and backed by Amazon's DynamoDB accessed through boto.

对于特定的用例，我们需要从a中检索一个值表，然后使其对其他用户不可用。

For a specific use case, we need to retrieve a value from a table and then make it unavailable for other users.

但是，通过检索然后删除该值，在检索和删除之间可能会出现竞争条件。

However, by retrieving and then deleting the value, a race-condition could occur in between the retrieval and deletion.

有什么方法可以从表中检索项目并立即以原子方式删除或更新它？

Is there any way to retrieve an item from a table and immediately delete or update it in an atomic fashion?

推荐答案

如果您的逻辑是

1. 获取项目


2. delete

没有任何其他逻辑来确定是否应该删除，那么您实际上可以立即发送删除请求，下面是示例（尚未检查，通常取自： http://docs.aws .amazon.com / amazondynamodb / latest / developerguide / LowLevelJavaItemCRUD.html ）

without any additional logic to determine whether deletion should occur, then you can actually send delete request immediately, here is example (I haven't checked it, mostly take from: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/LowLevelJavaItemCRUD.html)

HashMap<String, AttributeValue> key = new HashMap<String, AttributeValue>();
key.put("Id", new AttributeValue().withN("101"));

DeleteItemRequest deleteItemRequest = new DeleteItemRequest()
    .withTableName(tableName)
    .withKey(key)
    .withReturnValues(ReturnValue.ALL_OLD);

DeleteItemResult deleteItemResult = client.deleteItem(deleteItemRequest);
Map<String,AttributeValue> deletedItem = deleteItemResult.getAttributes();

文档：

withReturnValues

getAttributes

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