DynamoDB mapper conditional save failing for new row updates - amazon-dynamodb

Question

Assume I have the following table in DDB. One hashkey (Lets call it 'Name'), one range key (lets call it 'Activity'), and one attribute (lets call it 'Date')
|---------------------|------------------|------------------|
| HashKey(S) | RangeKey(S) | Date(S) |
|---------------------|------------------|------------------|
| Sam | Fishing | 2019 |
|---------------------|------------------|------------------|
| Sam | Kayaking | 2019 |
|---------------------|------------------|------------------|
| Peter | Kayaking | 2019 |
|---------------------|------------------|------------------|
I want to do a conditional save on this such that I want to add a new "name + activity" and keep the most up to date date in the DB. So a breakdown of the 2 possibilities would be
1) If there is an existing hash+rangekey already based on what I have passed into the save, I want to check my condition expression and not update if it fails.
2) If it is a new hash+rangekey, I want a new row to be created, and not check my condition expression (since there are no values in the table to check on)
An example of what I tried
public void methodToDoSave() {
final Map<String, ExpectedAttributeValue> expectedAttributes =
getExpectedAttributes(date);
final DynamoDBSaveExpression saveExpression = new DynamoDBSaveExpression()
.withExpected(expectedAttributes);
mapper.save(dbItem, saveExpression);
}
private Map<String, ExpectedAttributeValue> getExpectedAttributes(
final Date date){
final Map expectedAttributeSetupForConditionalUpdate = new HashMap();
expectedAttributeSetupForConditionalUpdate
.put("Date",new ExpectedAttributeValue(new AttributeValue().withS(date))
.withComparisonOperator(ComparisonOperator.LE));
return expectedAttributeSetupForConditionalUpdate;
}
This works fine for doing the conditional checking and success/pass when the hash+range key is already in the table, however if I supply a new range key, the conditional check seems to always fail.
The stack trace for the conditional check is not that useful to explain to me the problem but my assumption is that the conditional check is being applied even for brand new row creations and so it is failing.
Is there a way to get this working in one save operation or will I need to read first, check if exists, if yes then save without the conditional checks, if no save with the conditional checks ?

Answer 1

I was able to leverage Tawan's hint above and do something like this.
final Map expectedAttributeSetupForConditionalUpdate = new HashMap();
expectedAttributeSetupForConditionalUpdate
.put("name", new ExpectedAttributeValue().withExists(false));
expectedAttributeSetupForConditionalUpdate
.put("activity", new ExpectedAttributeValue().withExists(false));
expectedAttributeSetupForConditionalUpdate
.put("Date", new ExpectedAttributeValue(new AttributeValue().withS(date))
.withComparisonOperator(ComparisonOperator.LE));
final DynamoDBSaveExpression saveExpression = new DynamoDBSaveExpression() .withExpected(expectedAttributeSetupForConditionalUpdate)
.withConditionalOperator(ConditionalOperator.OR);
I wasn't able to use the newer Condition expressions since DynamoDB mapper doesn't support them yet in the version I'm using. Essentially this "passes" the conditional check when the row doesn't exist, but uses the date when it does exist.