Add support for DynamoDBAutoGeneratedTimestampAttribute and DynamoDbUpdateBehaviorAttribute

[irina-herciu]

Add

• support for the [DynamoDBAutoGeneratedTimestamp] attribute to the .NET SDK for DynamoDB, enabling automatic setting of timestamp fields during save operations. This feature aligns with the Java SDK's @DynamoDbAutoGeneratedTimestampAttribute.
• support for [DynamoDbUpdateBehavior] attribute to the .NET SDK for DynamoDB, enabling update behavior for a property when performing DynamoDB update operations. This feature aligns with the Java SDK's @DynamoDbUpdateBehavior.

Description

• New Attributes: [DynamoDBAutoGeneratedTimestamp] and [DynamoDbUpdateBehavior]

  • [DynamoDBAutoGeneratedTimestamp] Automatically sets the property to the current UTC timestamp (DateTime.UtcNow) on item save.
  • [DynamoDbUpdateBehavior] Specifies the update behavior for a property when performing DynamoDB update operations. This attribute can be used to control whether a property is always updated, only updated if not null.

• Update Behavior Modes:

  • IfNotExists: Set the value only when the item is created.
  • Always: Set the value on both create and update.

• Usage:

  class Order
  {
      [DynamoDBHashKey]
      public string Id { get; set; }
  
      [DynamoDBAutoGeneratedTimestamp]
      [DynamoDbUpdateBehavior(UpdateBehavior.IfNotExists)]
      public DateTime CreatedAt { get; set; }
  
      [DynamoDBAutoGeneratedTimestamp]
      [DynamoDBProperty(StoreAsEpoch = true)]
      public DateTime? UpdatedAt { get; set; }
  }

Motivation and Context

Testing

unit and integration tests added

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]

I don't see the code paths updated for the batch and transact write operations.

[irina-herciu]

I don't see the code paths updated for the batch and transact write operations.

Transact write operation is updated and there is an integration test added - Test_AutoGeneratedTimestampAttribute_TransactWrite_Simple

Batch write operation does not offer support for autogenerated values as the operation does not support update expressions and this behavior is consistent with the Java SDK as well as DynamoDBVersionAttribute.

[irina-herciu]

after testing, looks like Batch write operation on Java SDK it offers support for autogenerated timestamps and ignores the DynamoDbUpdateBehavior. I will update the implementation to cover this.

[irina-herciu]

autogenerated timestamp implementation updated to cover also batch write operation