在 DynamoDB 中生成所需长度的 ID [英] Generating id's of desired length in DynamoDB

问题描述

我正在使用 Amazon DynamoDB，我需要一个对象的 id 长度为 10.我认为不可能告诉 Dynamo 自动生成这个长度的 id(如果我错了，我该怎么做)这个?)所以我在考虑使用我定义的长度为 10 的唯一字符串设置对象的字段.做这个的最好方式是什么?为此，自动增量是一个坏主意吗?

I'm working with Amazon DynamoDB and I need an object to have an id of length 10. I think is not possible to tell Dynamo to auto-generate id's of this length (if I'm wrong, how can I do this?) so I was thinking about setting a field of the object with a unique string of length 10 defined by me. What is the best way to do this? Is auto increment a bad idea for this purpose?

推荐答案

DynamoDB 没有任何机制来为新项目生成唯一 ID.但是，您几乎不需要这样的功能，因为您的应用程序可以轻松生成一个 10 字节的随机字符串并将其用作新项的键.

DynamoDB does not have any mechanism for generating unique ids for new items. However, you hardly need such a feature, because your application can easily generate a 10-byte random string and use that as the key for the new item.

如果您担心一百年一次，这个随机密钥会与已经存在的项目的密钥发生冲突，这也很容易解决:您可以在 ConditionExpression 中使用 ConditionExpressioncode>PutItem 要求仅创建不存在的项目:

If you're worried that once in a hundred years, this random key will collide with the key of an item that already exists, that's easy to solve too: You can use a ConditionExpression in PutItem to ask to only create the item if it doesn't already exist:

1. 条件可以是 id <>:id，其中 id 是键列，:id 是我们尝试创建的随机 ID.如果该项目存在(该值不等于本身)，这将失败，但如果该项目不存在，则会成功(如果该项目不存在，则认为它不等于任何东西).
2. 或者更简单，使用条件attribute_not_exists(id).如果该项目不存在，则attribute_not_exists"check 会成功，但如果该项目确实存在，显然它的主键存在，因此 attribute_not_exists 条件将失败.

1. The condition can be that id <> :id, where id is the key column and :id is the random id we're trying to create. This will fail if the item exists (the value isn't not-equal itself), but will succeed if the item doesn't exist (if the item doesn't exist, it's considered not equal to anything).
2. Or even simpler, use the condition attribute_not_exists(id). If the item doesn't exist, the "attribute_not_exists" check will succeed, but if the item does exist, obviously its primary key exists so the attribute_not_exists condition will fail.

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