Add support for DynamoDBAutoGeneratedTimestampAttribute and DynamoDbUpdateBehaviorAttribute #3892

irina-herciu · 2025-06-23T11:56:55Z

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.

sdk/src/Services/DynamoDBv2/Custom/DataModel/ContextInternal.cs

irina-herciu · 2025-07-15T11:27:35Z

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 · 2025-07-18T13:11:02Z

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 · 2025-07-21T13:28:51Z

autogenerated timestamp implementation updated to cover also batch write operation

Copilot

Pull Request Overview

This PR adds two new attributes to the .NET SDK for DynamoDB to align with Java SDK functionality: [DynamoDBAutoGeneratedTimestamp] and [DynamoDbUpdateBehavior]. The auto-generated timestamp attribute automatically sets DateTime properties to the current UTC timestamp during save operations, while the update behavior attribute controls when properties are updated (Always or IfNotExists).

Key Changes:

Added DynamoDBAutoGeneratedTimestampAttribute and DynamoDbUpdateBehaviorAttribute classes with validation logic
Extended PropertyStorage to support timestamp auto-generation and update behavior modes
Modified save operations to handle timestamp generation and conditional updates using if_not_exists DynamoDB expressions

Reviewed Changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
Attributes.cs	Adds new attribute classes with proper constructors and enum definitions
InternalModel.cs	Extends PropertyStorage with timestamp and update behavior properties plus validation
ContextInternal.cs	Implements timestamp generation logic during object serialization
Context.cs	Updates save operations to handle conditional update behaviors
Utils.cs	Adds timestamp type validation helper method
Table.cs	Modifies update operations to support if_not_exists conditions
Util.cs	Updates expression building to handle conditional attribute updates
Expression.cs	Adds utility method to merge update expressions
DocumentTransactWrite.cs	Extends transactional writes to support conditional updates
TransactWrite.cs	Updates transactional operations to use new conditional logic
Multiple test files	Comprehensive unit and integration tests for new functionality

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Copilot · 2025-08-19T02:29:30Z

sdk/src/Services/DynamoDBv2/Custom/DataModel/Utils.cs

+                (memberType.IsAssignableFrom(typeof(DateTime)) ||
+                memberType.IsAssignableFrom(typeof(DateTimeOffset))))
+            {
+                return;


The validation logic for timestamp types is incorrect. IsAssignableFrom checks if the current type can be assigned from the parameter type, but here you want to check if the nullable's underlying type is DateTime or DateTimeOffset. Use memberType.GetGenericArguments()[0] to get the underlying type and check if it equals typeof(DateTime) or typeof(DateTimeOffset).

Suggested change

return;

if (memberType.IsGenericType && memberType.GetGenericTypeDefinition() == typeof(Nullable<>))

{

var underlyingType = memberType.GetGenericArguments()[0];

if (underlyingType == typeof(DateTime) || underlyingType == typeof(DateTimeOffset))

{

return;

}

Copilot · 2025-08-19T02:29:30Z

sdk/src/Services/DynamoDBv2/Custom/DocumentModel/Util.cs

+            }
+            else
+            {
+                var setStatement = updateExpression != null ? updateExpression.ExpressionStatement : "";


When sets.Length == 0 but there's an existing updateExpression, the code appends just the existing expression statement without proper SET keyword handling. This could result in malformed update expressions. The logic should handle merging existing expressions more carefully.

Copilot · 2025-08-19T02:29:31Z

sdk/src/Services/DynamoDBv2/Custom/DataModel/ContextInternal.cs

+
+                        if (dbe == null && propertyStorage.IsAutoGeneratedTimestamp)
+                        {
+                            document[attributeName] = new Primitive(now.ToString("o"));


The timestamp is always stored as an ISO string regardless of the property's storage configuration (StoreAsEpoch, StoreAsEpochLong). This will cause inconsistent storage formats. The code should respect the property's storage settings and convert to epoch time when appropriate.

Suggested change

document[attributeName] = new Primitive(now.ToString("o"));

if (propertyStorage.StoreAsEpoch)

{

// Store as seconds since Unix epoch (int)

var epochSeconds = (int)(now - DateTime.UnixEpoch).TotalSeconds;

document[attributeName] = new Primitive(epochSeconds);

}

else if (propertyStorage.StoreAsEpochLong)

{

// Store as milliseconds since Unix epoch (long)

var epochMilliseconds = (long)(now - DateTime.UnixEpoch).TotalMilliseconds;

document[attributeName] = new Primitive(epochMilliseconds);

}

else

{

// Store as ISO string

document[attributeName] = new Primitive(now.ToString("o"));

}

Copilot · 2025-08-19T02:29:31Z

sdk/src/Services/DynamoDBv2/Custom/DocumentModel/Expression.cs

+                keywordsOrder.Where(k => mergedSections.ContainsKey(k))
+                             .Select(k => $"{k} {mergedSections[k]}"));
+
+            var mergedNames = Common.Combine(left.ExpressionAttributeNames, right.ExpressionAttributeNames, StringComparer.Ordinal); ;


There's an extra semicolon at the end of the line, creating a redundant empty statement.

Suggested change

var mergedNames = Common.Combine(left.ExpressionAttributeNames, right.ExpressionAttributeNames, StringComparer.Ordinal); ;

var mergedNames = Common.Combine(left.ExpressionAttributeNames, right.ExpressionAttributeNames, StringComparer.Ordinal);

Copilot · 2025-08-19T02:29:31Z

sdk/src/Services/DynamoDBv2/Custom/DataModel/InternalModel.cs

@@ -231,6 +237,11 @@ public void Validate(DynamoDBContext context)
            if (IsHashKey && IsRangeKey)
                throw new InvalidOperationException("Property " + PropertyName + " cannot be both hash and range key");

+            if (UpdateBehaviorMode == UpdateBehavior.IfNotExists && (IsKey || IsVersion || IsCounter))
+            {
+                throw new InvalidOperationException("Property " + PropertyName + " cannot be a key and have UpdateBehavior set to IfNotExists at the same time.");


[nitpick] The validation logic could be more descriptive by specifying which specific property type (key, version, or counter) is incompatible with IfNotExists behavior in the exception message.

Suggested change

throw new InvalidOperationException("Property " + PropertyName + " cannot be a key and have UpdateBehavior set to IfNotExists at the same time.");

string propertyType = IsKey ? "key" : IsVersion ? "version" : IsCounter ? "counter" : "unknown";

throw new InvalidOperationException($"Property {PropertyName} cannot be a {propertyType} and have UpdateBehavior set to IfNotExists at the same time.");

GarrettBeatty · 2025-08-19T17:15:15Z

@irina-herciu is it possible to split this into two PRs? one for the DynamoDBAutoGeneratedTimestampAttribute and one for the other attribute? it will make it easier for me to review

irina-herciu added 5 commits June 16, 2025 13:26

add new attribute

1c95be4

handle autogenerated timestamp

5f4d362

Add changelog

e6ceb76

add DynamoDbUpdateBehaviorAttribute

2d61f5c

unit testing

610a441

irina-herciu changed the title ~~Add support for DynamoDBAutoGeneratedTimestampAttribute that sets current timestamp during persistence operations.~~ Add support for DynamoDBAutoGeneratedTimestampAttribute and DynamoDbUpdateBehaviorAttribute Jul 7, 2025

irina-herciu marked this pull request as ready for review July 7, 2025 15:30

merge from development

88c6a23

normj self-requested a review July 15, 2025 00:38

normj reviewed Jul 15, 2025

View reviewed changes

sdk/src/Services/DynamoDBv2/Custom/DataModel/ContextInternal.cs Outdated Show resolved Hide resolved

remove unused method

ab5d959

irina-herciu added 4 commits July 21, 2025 11:44

merge from development

a6eb164

fix build

1d79891

autogenerate timestamp for batchwrite

8b0f1df

unit tests

868d87b

GarrettBeatty requested review from Copilot and GarrettBeatty August 19, 2025 02:28

Copilot AI reviewed Aug 19, 2025

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Add support for DynamoDBAutoGeneratedTimestampAttribute and DynamoDbUpdateBehaviorAttribute #3892

Add support for DynamoDBAutoGeneratedTimestampAttribute and DynamoDbUpdateBehaviorAttribute #3892

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irina-herciu commented Jun 23, 2025 •

edited

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-                return;
+            if (memberType.IsGenericType && memberType.GetGenericTypeDefinition() == typeof(Nullable<>))
+            {
+                var underlyingType = memberType.GetGenericArguments()[0];
+                if (underlyingType == typeof(DateTime) || underlyingType == typeof(DateTimeOffset))
+                {
+                    return;
+                }

-                            document[attributeName] = new Primitive(now.ToString("o"));
+                            if (propertyStorage.StoreAsEpoch)
+                            {
+                                // Store as seconds since Unix epoch (int)
+                                var epochSeconds = (int)(now - DateTime.UnixEpoch).TotalSeconds;
+                                document[attributeName] = new Primitive(epochSeconds);
+                            }
+                            else if (propertyStorage.StoreAsEpochLong)
+                            {
+                                // Store as milliseconds since Unix epoch (long)
+                                var epochMilliseconds = (long)(now - DateTime.UnixEpoch).TotalMilliseconds;
+                                document[attributeName] = new Primitive(epochMilliseconds);
+                            }
+                            else
+                            {
+                                // Store as ISO string
+                                document[attributeName] = new Primitive(now.ToString("o"));
+                            }

	var mergedNames = Common.Combine(left.ExpressionAttributeNames, right.ExpressionAttributeNames, StringComparer.Ordinal); ;
	var mergedNames = Common.Combine(left.ExpressionAttributeNames, right.ExpressionAttributeNames, StringComparer.Ordinal);

	throw new InvalidOperationException("Property " + PropertyName + " cannot be a key and have UpdateBehavior set to IfNotExists at the same time.");
	string propertyType = IsKey ? "key" : IsVersion ? "version" : IsCounter ? "counter" : "unknown";
	throw new InvalidOperationException($"Property {PropertyName} cannot be a {propertyType} and have UpdateBehavior set to IfNotExists at the same time.");

Add support for DynamoDBAutoGeneratedTimestampAttribute and DynamoDbUpdateBehaviorAttribute #3892

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Add support for DynamoDBAutoGeneratedTimestampAttribute and DynamoDbUpdateBehaviorAttribute #3892

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Description

Motivation and Context

Testing

Screenshots (if appropriate)

Types of changes

Checklist

License

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irina-herciu commented Jul 15, 2025

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Pull Request Overview

Key Changes:

Reviewed Changes

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irina-herciu commented Jun 23, 2025 •

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