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