Features/dynamo db update behavior attribute

[irina-herciu]

Add 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 Attribute: [DynamoDbUpdateBehavior]

• [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

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

[Copilot]

Pull Request Overview

This PR adds support for the [DynamoDbUpdateBehavior] attribute to the .NET SDK for DynamoDB, enabling control over property update behavior during DynamoDB update operations. The feature aligns with the Java SDK's @DynamoDbUpdateBehavior annotation and introduces an IfNotExists mode that sets property values only when items are created (not on updates), alongside the default Always mode.

Key Changes

• New DynamoDbUpdateBehaviorAttribute and UpdateBehavior enum to specify update behavior (Always/IfNotExists)
• Updates to the update expression generation logic to support conditional if_not_exists clauses for properties marked with IfNotExists behavior
• Integration with existing auto-generated timestamp functionality to enable create-only timestamp tracking

Reviewed Changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
sdk/src/Services/DynamoDBv2/Custom/DataModel/Attributes.cs	Adds new DynamoDbUpdateBehaviorAttribute and UpdateBehavior enum
sdk/src/Services/DynamoDBv2/Custom/DataModel/InternalModel.cs	Adds UpdateBehaviorMode property to PropertyStorage and validation logic
sdk/src/Services/DynamoDBv2/Custom/DataModel/ContextInternal.cs	Implements GetUpdateIfNotExistsAttributeNames helper to identify properties with IfNotExists behavior
sdk/src/Services/DynamoDBv2/Custom/DataModel/Context.cs	Updates save operations to pass IfNotExists attribute names to update helpers
sdk/src/Services/DynamoDBv2/Custom/DataModel/TransactWrite.cs	Updates transact write to support IfNotExists attributes
sdk/src/Services/DynamoDBv2/Custom/DocumentModel/Table.cs	Modifies UpdateHelper methods to accept and process IfNotExists attribute names
sdk/src/Services/DynamoDBv2/Custom/DocumentModel/Util.cs	Updates expression generation to wrap IfNotExists attributes in if_not_exists() function
sdk/src/Services/DynamoDBv2/Custom/DocumentModel/Expression.cs	Adds MergeUpdateExpressions method for combining multiple update expressions
sdk/src/Services/DynamoDBv2/Custom/DocumentModel/DocumentTransactWrite.cs	Updates transact write document operations to support IfNotExists attributes
sdk/src/Services/DynamoDBv2/Custom/DataModel/Utils.cs	Updates error message for validation
sdk/test/Services/DynamoDBv2/UnitTests/Custom/DataModel/ContextInternalTests.cs	Adds unit tests for GetUpdateIfNotExistsAttributeNames functionality
sdk/test/Services/DynamoDBv2/UnitTests/Custom/DocumentModel/TableTests.cs	New test file covering various update scenarios with and without IfNotExists attributes
sdk/test/Services/DynamoDBv2/UnitTests/Custom/DocumentModel/ExpressionsTest.cs	New test file for expression merging functionality
sdk/test/Services/DynamoDBv2/IntegrationTests/DataModelTests.cs	Updates integration tests to verify IfNotExists behavior with auto-generated timestamps
generator/.DevConfigs/9490947f-209f-47e9-8c70-3698872df304.json	Adds dev config for minor version bump

[GarrettBeatty]

ill give this a review later this week. thanks for the pr!