如何在 dynamodb 中的属性上插入具有增量值的项目

Question

I'd like to achieve the self incremental feature like mysql in Dynamodb . After some search, I can only use updateItem with an update expression like { ":inc": {N: "1"} } . But it only works for updating an existing item. What I want to achieve is to increase a version field by 1 whenever we insert a new item on dynamodb.

Is there a buildin feature in dynamodb to achieve this?

Answer 1

DynamoDB does not have an auto incrementing count feature, you'll have to implement that yourself.

You could handle this in a transaction, where you insert a new item into DDB and then increment the version field by 1. This approach has the side effect of making sure the version only increases if the PutItem operation succeeds. This is useful when you include a ConditionExpression in the PutItem call to enforce any other business logic. If the condition fails, the version will not be incremented.

You could go one step further and implement a strategy known as Optomistic Locking. You would read the version field before calling updateItem . In the call to updateItem , you would use a conditionExpression to ensure the number is what you expect. If another process updated the version, it will fail the condition check and your updateItem will fail. You could try the operation again until you get the outcome you expect.

More info about Optimistic Locking: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/DynamoDBMapper.OptimisticLocking.html