DynamoDb Java API

DynamoDb Java API - 如果计数器增量不存在则插入(DynamoDb Java API - Insert if does not exist on counter increment)

我试图插入项目，如果它不存在，并将其计数器设置为1或在它存在时递增计数器，但它似乎不起作用...

这是我到目前为止所做的：

UpdateItemSpec updateItemSpec = new UpdateItemSpec() .withPrimaryKey("Id", Id) .withReturnValues(ReturnValue.ALL_NEW) .withUpdateExpression("set #c = if_not_exists(#c = :val, #c + :val)") .withNameMap(new NameMap() .with("#c", "counter")) .withValueMap(new ValueMap() .withNumber(":val", 1));

当我更改更新表达式以设置#c = #c +：val时，它会更新现有项目，但如果它不存在则不会插入新项目。

设置#c =：val似乎既可以存在又不存在，但这不是我需要的。

I am trying to insert item if it does not exist and set its counter to 1 or increment counter by one when it exists but it doesn't seem to work...

Here is what I have done so far:

UpdateItemSpec updateItemSpec = new UpdateItemSpec() .withPrimaryKey("Id", Id) .withReturnValues(ReturnValue.ALL_NEW) .withUpdateExpression("set #c = if_not_exists(#c = :val, #c + :val)") .withNameMap(new NameMap() .with("#c", "counter")) .withValueMap(new ValueMap() .withNumber(":val", 1));

when I change the update expression to set #c = #c + :val it updates existing items but it doesn't insert new item if it does not exist.

set #c = :val seems to work on both exist and not exist but that's not what I need.

最满意答案

您可以使用一个UpdateItem调用创建和更新项目。 UpdateExpression将是ADD #c :val因为DynamoDB假装在对尚不存在的项的ADD操作中Number的值为零。

You can create and update the item with one UpdateItem call. UpdateExpression would be ADD #c :val because DynamoDB pretends the value of a Number is zero in ADD operations on items that do not exist yet.