Issues/224 atomic counter attribute

[irina-herciu]

Introduce support for the [DynamoDBAtomicCounter] attribute in the DynamoDB Object Persistence Model for the AWS SDK for .NET. This feature brings parity with the Java SDK V2, which supports atomic counters via @DynamoDbAtomicCounter.

java DynamoDbAtomicCounter
Using atomic counters

Description

• New attribute: DynamoDBAtomicCounterAttribute, to mark numeric properties for auto-increment behavior
• Updates to DynamoDBContext and internal mapping to detect and apply counter increment behavior during save item operation

class Session {
    [DynamoDBHashKey]
    public string Id { get; set; }

    [DynamoDBAtomicCounter]
    public int RetryCount { get; set; }

    // This field starts from 100 and increments by 5 on each save
    [DynamoDBAtomicCounter(delta:5, startValue:100)] 
    public long Views { get; set; }
}

On context.SaveAsync(session), it will automatically be incremented in DynamoDB using the appropriate SET operation.

Motivation and Context

Testing

Integration test added
Unit test to be added for internal methods

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have read the README document
• I have added tests to cover my changes
• All new and existing tests passed

License

• I confirm that this pull request can be released under the Apache 2 license

[normj]

Shouldn't this be called counterAttributeName?

[normj]

Curious how this compares to Java V2. But if I set the StartValue to 3 and Delta to 5 when I save my first version of the object I get 8. I would expect 3 after the first save and 8 with the second save. If this is consistent with Java we need to make sure the docs on the StartValue and Delta are clear this is how it works.

[irina-herciu]

first save will be 3 as the value in ExpressionAttributeValues is CounterStartValue-CounterDelta so that the increment can be done correctly. This is the same behavior as in Java V2.

[normj]

If I understand correctly this increment is for getting the in memory updated to what the value will be incremented to. But what if the in memory value is behind what is in DynamoDB? If I'm understanding that correctly this seems bad. If I'm misunderstanding this then the logic needs more doc comments.