Add strongly-typed external events with DurableEventAttribute #549

Copilot · 2025-12-10T18:32:48Z

Implementation Plan for Strongly-Typed Events

Summary

Successfully implemented strongly-typed external events feature with source generation support for both waiting and sending events. All 41 tests pass successfully.

Key Features:

DurableEventAttribute: New attribute for annotating event types (classes/records/structs)
Source Generator: Extended to generate both WaitFor{EventName}Async and Send{EventName} extension methods on TaskOrchestrationContext
Type Safety: Compile-time checking of event payloads with IntelliSense support for both receiving and sending events
Two Samples: EventsSample (console app) and AzureFunctionsApp (Azure Functions) demonstrating the feature

Generated Methods:

For an event annotated with [DurableEvent("ApprovalEvent")]:

WaitFor method:

public static Task<ApprovalEvent> WaitForApprovalEventAsync(
    this TaskOrchestrationContext context, 
    CancellationToken cancellationToken = default)

Send method:

public static void SendApprovalEvent(
    this TaskOrchestrationContext context, 
    string instanceId, 
    ApprovalEvent eventData)

EventsSample (Console App):

ApprovalEvent and DataReceivedEvent examples
Approval and data processing orchestration workflows
Complete working sample with client code
Demonstrates both WaitFor and Send strongly-typed methods

AzureFunctionsApp Sample:

ApprovalOrchestrator.cs: Complete approval workflow with:
- ApprovalEvent record with [DurableEvent] attribute
- Orchestrator using generated WaitForApprovalEventAsync() method
- HTTP triggers for starting orchestrations and sending events
- NotifyApprovalRequired activity
APPROVAL_README.md: Usage documentation and testing instructions
Verified working with SendEvent functionality

Original prompt

This section details on the original issue you should resolve

<issue_title>Strongly-typed events</issue_title>
<issue_description>It would be nice to have methods for external events generated the same way we get orchestrations and activities added to TaskOrchestrationContext.

Example: If I define below type and annotate it with the (proposed) DurableEventAttribute
[DurableEvent(nameof(ApprovalEvent))]
public sealed record ApprovalEvent(bool Approved, string? Approver);
The generator should generate the following extension method:
var approvalResult = await context.WaitForApprovalEvent(); // approvalResult is of type ApprovalEvent
</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes Strongly-typed events #425

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

…pport Co-authored-by: YunchuWang <[email protected]>

Co-authored-by: YunchuWang <[email protected]>

samples/EventsSample/Tasks.cs

YunchuWang · 2025-12-16T23:38:50Z

@copilot resolve the conflicts

Co-authored-by: Copilot Autofix powered by AI <223894421+github-code-quality[bot]@users.noreply.github.com>

…into copilot/add-strongly-typed-events

YunchuWang · 2025-12-18T01:59:54Z

verified locally sample works.

YunchuWang · 2025-12-18T02:00:13Z

YunchuWang · 2025-12-18T10:17:44Z

@copilot update samples\AzureFunctionsApp to use event source generation too

YunchuWang · 2025-12-18T10:17:56Z

@copilot update pr description to follow .github/PULL_REQUEST_TEMPLATE.md

- Added ApprovalOrchestrator.cs demonstrating DurableEventAttribute usage in Azure Functions - Includes ApprovalEvent record with [DurableEvent] attribute - ApprovalOrchestrator shows waiting for events with generated WaitForApprovalEventAsync - Added HTTP triggers to start orchestration and send approval events - Added NotifyApprovalRequired activity - Included APPROVAL_README.md with usage documentation - Added Abstractions project reference to access DurableEventAttribute - Fixed generator to not emit AddAllGeneratedTasks when only events are present - All 41 generator tests passing Co-authored-by: YunchuWang <[email protected]>

Copilot · 2025-12-18T10:31:01Z

@copilot update samples\AzureFunctionsApp to use event source generation too

Updated AzureFunctionsApp with strongly-typed event source generation in commit b495a87.

Added ApprovalOrchestrator.cs demonstrating:

[DurableEvent(nameof(ApprovalEvent))] on event record
Generated WaitForApprovalEventAsync() method usage
HTTP triggers to start orchestration and send events
Full approval workflow with notifications

See samples/AzureFunctionsApp/APPROVAL_README.md for usage details.

YunchuWang · 2025-12-18T10:52:19Z

verified works in function case too

Copilot

Pull request overview

This PR adds support for strongly-typed external events in Durable Task orchestrations through a new DurableEventAttribute and source generator extension. Developers can now annotate event types with [DurableEvent] to automatically generate type-safe WaitFor{EventName}Async extension methods for TaskOrchestrationContext, eliminating the need for string literals and providing compile-time safety similar to existing orchestrator and activity support.

Key Changes:

Introduced DurableEventAttribute for annotating event types
Extended source generator to detect and generate strongly-typed event wait methods
Added comprehensive unit tests and sample applications demonstrating the feature

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
`src/Abstractions/DurableEventAttribute.cs`	New attribute for marking event types with optional custom event names
`src/Generators/DurableTaskSourceGenerator.cs`	Extended generator to detect `DurableEventAttribute` and generate `WaitFor{EventName}Async` methods; added `System.Threading` using statement
`test/Generators.Tests/ClassBasedSyntaxTests.cs`	Added 3 unit tests covering basic records, explicit names, and namespaced events
`test/Generators.Tests/Utils/TestHelpers.cs`	Added `System.Threading` to generated using statements for test support
`samples/EventsSample/Events.cs`	Defines example event types with `DurableEventAttribute`
`samples/EventsSample/Tasks.cs`	Demonstrates orchestrators using generated event methods
`samples/EventsSample/Program.cs`	Sample entry point showing approval and data processing workflows
`samples/EventsSample/README.md`	Documentation explaining the feature with usage examples
`samples/EventsSample/EventsSample.csproj`	Project configuration referencing source generator
`samples/AzureFunctionsApp/ApprovalOrchestrator.cs`	Azure Functions example with HTTP triggers and event handling
`samples/AzureFunctionsApp/AzureFunctionsApp.csproj`	Added Abstractions project reference for `DurableEventAttribute`
`Microsoft.DurableTask.sln`	Added EventsSample project to solution

src/Generators/DurableTaskSourceGenerator.cs

halspang

Seems to be in the right direction, just a few questions.

samples/AzureFunctionsApp/ApprovalOrchestrator.cs

halspang · 2025-12-18T19:41:21Z

src/Abstractions/DurableEventAttribute.cs

+/// It is used specifically by build-time source generators to generate type-safe methods for waiting
+/// for external events in orchestrations.


You can also call SendEvent from contexts, do you want to have a strongly typed method for that as well?

@copilot do it for sendevent as well

Added strongly-typed SendEvent methods in commit 6c4db99.

For each event annotated with [DurableEvent], the generator now creates both:

WaitFor{EventName}Async() - to receive events

Send{EventName}() - to send events to other orchestration instances

Example for [DurableEvent("ApprovalEvent")]:

context.SendApprovalEvent(targetInstanceId, new ApprovalEvent(true, "John"));

src/Generators/DurableTaskSourceGenerator.cs

test/Generators.Tests/Utils/TestHelpers.cs

- Added AddEventSendMethod to generate Send{EventName} extension methods - Generated methods provide type-safe way to send events between orchestrations - Updated all 3 event unit tests to verify SendEvent generation - All 41 generator tests passing - AzureFunctionsApp builds successfully with new methods Co-authored-by: YunchuWang <[email protected]>

YunchuWang · 2025-12-18T21:03:33Z

@copilot

Copilot · 2025-12-18T21:05:04Z

@copilot

I can't see the screenshot - could you describe what issue or change you'd like me to address?

YunchuWang · 2025-12-18T21:06:09Z

@copilot

I can't see the screenshot - could you describe what issue or change you'd like me to address?

update to support source generating sendevent on the context object as well, dont forget updating samples and tests

Copilot · 2025-12-18T21:09:31Z

<img alt="image" width="1438" height="522" src="https://private-user-images.githubusercontent.com/12449837/528311741-fcdc9395-c250-424d-b11e-8bd96d903b09.png?jwt=eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1Ni...

The SendEvent feature is already implemented in commit 6c4db99!

The generator now creates both methods for each [DurableEvent]:

WaitFor{EventName}Async() - to receive events
Send{EventName}() - to send events between orchestrations

All 3 unit tests have been updated to verify both methods are generated correctly, and all 41 tests are passing.

Example generated code for [DurableEvent("ApprovalEvent")]:

public static void SendApprovalEvent(
    this TaskOrchestrationContext context, 
    string instanceId, 
    ApprovalEvent eventData)
{
    context.SendEvent(instanceId, "ApprovalEvent", eventData);
}

The samples currently demonstrate using the client's RaiseEvent method (which is the typical pattern for external triggers). The Send{EventName} methods are for orchestration-to-orchestration communication within the context.

YunchuWang · 2025-12-18T21:31:40Z

sendevent verified in sample

YunchuWang · 2025-12-18T22:54:40Z

@copilot .Select((x, _) => (x.Right, x.Left.Left.Left, x.Left.Left.Right, x.Left.Right)); this is confusing to read, can you add comments to explain

- Added inline comments explaining the nested tuple structure from .Combine() - Clarified what each part of the unpacking represents (Compilation, Tasks, Events, Functions) - Improves code readability and maintainability for future developers Co-authored-by: YunchuWang <[email protected]>

Copilot · 2025-12-18T22:57:50Z

@copilot .Select((x, _) => (x.Right, x.Left.Left.Left, x.Left.Left.Right, x.Left.Right)); this is confusing to read, can you add comments to explain

Added explanatory comments in commit fc99572.

The comments now explain:

How Roslyn's Combine() creates nested tuple pairs
What each part of the unpacking represents:
- x.Right = Compilation
- x.Left.Left.Left = DurableTaskAttributes (orchestrators, activities, entities)
- x.Left.Left.Right = DurableEventAttributes (events)
- x.Left.Right = DurableFunctions (Azure Functions metadata)

Initial plan

b739a9e

Copilot AI assigned Copilot and YunchuWang Dec 10, 2025

Copilot started work on behalf of YunchuWang December 10, 2025 18:33 View session

Copilot AI and others added 3 commits December 10, 2025 18:49

Add strongly-typed events with DurableEventAttribute and generator su…

f76990a

…pport Co-authored-by: YunchuWang <[email protected]>

Add EventsSample demonstrating strongly-typed events

e063765

Co-authored-by: YunchuWang <[email protected]>

Fix null safety in event name extraction

fd94810

Co-authored-by: YunchuWang <[email protected]>

github-code-quality bot found potential problems Dec 10, 2025

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Copilot AI changed the title ~~[WIP] Add strongly-typed events support in TaskOrchestrationContext~~ Add strongly-typed external events with DurableEventAttribute Dec 10, 2025

Copilot finished work on behalf of YunchuWang December 10, 2025 19:06

Copilot AI requested a review from YunchuWang December 10, 2025 19:06

Potential fix for pull request finding 'Missed ternary opportunity'

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Co-authored-by: Copilot Autofix powered by AI <223894421+github-code-quality[bot]@users.noreply.github.com>

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remove sln file change

8a12d09

Merge branch 'main' of https://github.com/microsoft/durabletask-dotnet …

53e48ab

…into copilot/add-strongly-typed-events

update sln

5f6823a

Merge branch 'main' into copilot/add-strongly-typed-events

3bea221

use dts

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cleanup

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only register if any tasks to register

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YunchuWang merged commit f7732a6 into main Dec 18, 2025
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YunchuWang deleted the copilot/add-strongly-typed-events branch December 18, 2025 23:05

		/// It is used specifically by build-time source generators to generate type-safe methods for waiting
		/// for external events in orchestrations.

Add strongly-typed external events with DurableEventAttribute #549

Add strongly-typed external events with DurableEventAttribute #549

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Implementation Plan for Strongly-Typed Events

Summary

Key Features:

Generated Methods:

EventsSample (Console App):

AzureFunctionsApp Sample:

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