BbQ.Events.SourceGenerators 1.2.0

BbQ.Events.SourceGenerators

Source generators for BbQ.Events - Automatically discovers and registers event handlers, subscribers, and projection handlers.

All five Events packages share version 1.2.0 and are released together. See the GA release notes for upgrade and provider guidance.

Overview

This package contains Roslyn source generators that automatically discover implementations of IEventHandler<TEvent>, IEventSubscriber<TEvent>, IProjectionHandler<TEvent>, IPartitionedProjectionHandler<TEvent>, and IProjectionBatchHandler<TEvent> in your project and generate registration code.

Features

• Automatic Discovery: Finds all event handlers, subscribers, and projection handlers at compile-time
• Zero Configuration: No manual registration needed
• Type-Safe: Generates strongly-typed registration code
• Performance: No runtime reflection for handler discovery
• Projection Support: Discovers and registers all three projection handler types

Installation

This package is part of the Events 1.2.0 GA family and is automatically included when you reference BbQ.Events.

dotnet add package BbQ.Events.SourceGenerators --version 1.2.0

Usage

The source generator automatically creates extension methods for your assembly:

services.AddYourAssemblyNameEventHandlers();  // Registers event handlers and subscribers
services.AddYourAssemblyNameProjections();    // Registers projection handlers

Example

// Your event handler
public class SendWelcomeEmailHandler : IEventHandler<UserCreated>
{
    public Task Handle(UserCreated @event, CancellationToken ct)
    {
        // Handle the event
        return Task.CompletedTask;
    }
}

// Your event subscriber
public class UserAnalyticsSubscriber : IEventSubscriber<UserCreated>
{
    private readonly IEventBus _eventBus;

    public UserAnalyticsSubscriber(IEventBus eventBus)
    {
        _eventBus = eventBus;
    }

    public IAsyncEnumerable<UserCreated> Subscribe(CancellationToken ct)
        => _eventBus.Subscribe<UserCreated>(ct);
}

// Your projection handler (also auto-discovered)
[Projection("UserProfile")]
public class UserProfileProjection : IProjectionHandler<UserCreated>
{
    public Task HandleAsync(UserCreated @event, CancellationToken ct)
    {
        // Update read model...
        return Task.CompletedTask;
    }
}

// Registration (automatically generated)
services.AddInMemoryEventBus();
services.AddYourProjectNameEventHandlers(); // Auto-generated method
services.AddYourProjectNameProjections();   // Auto-generated method for projections

Generated Code

The generator creates a static class in the BbQ.Events.Configuration namespace with extension methods that register all discovered handlers and projections:

public static class GeneratedYourAssemblyEventRegistrationExtensions
{
    public static IServiceCollection AddYourAssemblyEventHandlers(
        this IServiceCollection services,
        ServiceLifetime handlersLifetime = ServiceLifetime.Scoped)
    {
        // Registers all IEventHandler<TEvent> implementations
        // Registers all IEventSubscriber<TEvent> implementations
        return services;
    }

    public static IServiceCollection AddYourAssemblyProjections(
        this IServiceCollection services)
    {
        // Registers all IProjectionHandler<TEvent> implementations
        // Registers all IPartitionedProjectionHandler<TEvent> implementations
        // Registers all IProjectionBatchHandler<TEvent> implementations
        return services;
    }
}

Customization

Handler Lifetime

By default, handlers are registered with ServiceLifetime.Scoped. You can change this:

services.AddYourAssemblyEventHandlers(ServiceLifetime.Transient);

Requirements

• .NET 8.0 or later
• C# 11 or later
• BbQ.Events package

How It Works

The source generator:

1. Scans your project for classes implementing IEventHandler<TEvent>, IEventSubscriber<TEvent>, IProjectionHandler<TEvent>, IPartitionedProjectionHandler<TEvent>, or IProjectionBatchHandler<TEvent>
2. Generates registration code at compile-time
3. Creates extension methods specific to your assembly name
4. No runtime reflection or assembly scanning required

License

This project is licensed under the MIT License.