DynamoDb Java API - Insert if does not exist on counter increment

Question

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.

Found the answer here stackoverflow.com/questions/32777374/… This is the right update expression ADD #c :val — Spyros El.
– Spyros El., Commented Dec 8, 2016 at 15:00

Alexander Patrikalakis · Accepted Answer · 2017-03-08 12:41:05Z

5

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.

answered Mar 8, 2017 at 12:41

Alexander Patrikalakis

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1 Comment

Blundell Over a year ago

following the question, the above as code is: .withUpdateExpression("ADD #c :val)")

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