EventSourcing.Events 8.2.0

EventSourcing

Overview

The EventSourcing library for .NET provides a robust, flexible, and efficient framework for implementing event sourcing in your .NET applications. This library facilitates capturing changes to an application's state as a series of events, allowing for easy auditing, debugging, and replaying of events to restore state.

Features

• EventBus: Efficiently publish and subscribe to events using an in-memory event bus with support for dependency injection (DI).
• CommandBus: Simplify command handling with a powerful command bus that supports both synchronous and asynchronous command execution.
• Queries: Separating queries from commands enhances maintainability, performance, scalability, security, and simplifies testing by clearly distinguishing between read and write operations.
• Concurrency Control: Manage concurrent command executions with built-in concurrency handling mechanisms to ensure data integrity.
• Extensibility: Easily extend and customize the framework to fit your specific needs, with interfaces and abstractions that promote clean architecture principles.
• Dependency Injection: Seamlessly integrate with the .NET dependency injection (DI) container to resolve and inject event and command handlers.

Handlers

• Visibility: All handlers must be public.

• Events Handlers: These are executed in parallel. If no public handlers are found, execution will complete without errors.

• Queries Handlers: Only one handler can be registered for each query type.

• Commands Handlers: These are also executed in parallel. For asynchronous execution, the system waits for all handlers to finish, and the response is taken from the first handler that completes.

• Concurrency Handlers: These handlers are executed in parallel, with concurrency control applied per handler type.

Dependency Injection

The EventSourcingExtensions class provides extension methods designed for configuring event sourcing within a .NET application. It facilitates the registration of event and command handlers into the dependency injection (DI) container. This is achieved by specifying an array of Type objects representing the types from which event or command handlers should be registered. This ensures that handlers are correctly resolved and utilized throughout the application.

Registration of handlers are categorized into:

• Command handlers: ICommandHandler<> and ICommandHandler<,>
• Concurrent command handlers: IConcurrentCommandHandler<,>
• Event handlers: IEventHandler<>

All identified handlers are registered as transient services in the DI container using the TryAddTransient method, which prevents duplicate registrations.

EventBus

The EventBus class supports both manual subscription of handlers for fine-grained control and automated registration via dependency injection (DI) for convenience and flexibility. This makes it suitable for implementing event-driven architectures and facilitating communication between different components of your application.

Features

• Manual Subscription: You can manually subscribe event handlers IEventHandler<TEvent> to specific generic event types TEvent using the Subscribe method. This allows precise control over which handlers receive which events.

• Dependency Injection (DI) Support: Alternatively, handlers can be automatically registered using the AddEventSourcing method from EventSourcingExtensions.

Key Points

• Concurrency: Utilizes ConcurrentDictionary for thread-safe handling of event handlers.
• Error Handling: Throws exceptions when attempting to publish an event without any registered handlers.
• Synchronously publishes: An event by invoking Publish on a background task.
• Asynchronous Handling: Supports asynchronous event handling via PublishAsync.

CommandBus

The CommandBus class facilitates the execution of commands within your application, supporting both simple and result-returning commands. It is designed to be flexible and extendable, allowing developers to easily integrate and manage command handling logic. Class supports both manual subscription of handlers for fine-grained control and automated registration via dependency injection (DI) for convenience and flexibility.

Features

• Manual Subscription: You can manually subscribe command handlers ICommandHandler<TCommand> to specific generic command types TCommand using the Subscribe method. This allows precise control over which handlers receive which commands.

• Dependency Injection (DI) Support: Alternatively, handlers can be automatically registered using the AddEventSourcing method from EventSourcingExtensions.

Key Points

• Concurrency: Utilizes ConcurrentDictionary for thread-safe handling of command handlers.
• Error Handling: Throws exceptions when attempting to execute a command without a registered handler or if the handler type does not match.
• Synchronously executes: An command by invoking Execute on a background task.
• Asynchronousle executes: Supports asynchronous command handling via ExecuteAsync.

Queries

• Separation of Concerns: Dividing queries from commands ensures a clear distinction between operations that change state (commands) and those that only retrieve data (queries). This separation enhances maintainability and readability of the code.
• Optimized Performance: Queries can be optimized for read performance, while commands can be optimized for write performance. This allows for more efficient handling of data access and modification.
• Scalability: Separating queries and commands allows for independent scaling. Read-heavy operations can be scaled differently from write-heavy operations, improving the overall performance and scalability of the system.
• Security and Validation: Commands often require validation and authorization checks before altering the state, while queries typically do not. This separation allows for more granular control over security policies.
• Simplified Testing: Dividing queries from commands simplifies unit testing. Queries can be tested independently of the state-changing logic, and vice versa, leading to more isolated and reliable tests.

Features

• Dependency Injection (DI) Support: Alternatively, handlers can be automatically registered using the AddEventSourcing method from EventSourcingExtensions.

Getting Started

For additional examples and usage details, please use EventSourcing.Api project.

Installation

Add the EventSourcing library to your project via NuGet:

dotnet add package EventSourcing

Usage

EventBus Setup

To set up the EventBus for managing events, you can use the following approach:

Define your custom events by implementing the respective interfaces:

public class UserRegisteredEvent : IEvent 
{
    public string UserId { get; set; }
    public DateTime RegisteredAt { get; set; }
}

Implement handlers for your events:

public class UserRegisteredEventHandler : IEventHandler<UserRegisteredEvent>
{
    public async Task HandleAsync(UserRegisteredEvent eventModel, CancellationToken ct = default)
    {
        // Handle the event
    }
}

Manually subscribe event handlers:

var eventBus = new EventBus();
eventBus.Subscribe(new UserRegisteredEvent());
await eventBus.PublishAsync(new UserRegisteredEvent());

Alternatively, use DI for automatic registration in your Program.cs:

services.AddEventSourcing(typeof(UserRegisteredEvent));
await new UserRegisteredEvent().PublishAsync();

Alternatively, register IEventBus to yor DI container:

services.AddSingleton<IEventBus, EventBus>();

Now publish events using the event bus:

var eventBus = serviceProvider.GetRequiredService<IEventBus>();
await eventBus.PublishAsync(new UserRegisteredEvent 
{
    UserId = "12345",
    RegisteredAt = DateTime.UtcNow
});

CommandBus Setup

To configure the CommandBus for executing commands, follow these steps:

Define your custom commands by implementing the respective interfaces:

public class RegisterUserCommand : ICommand 
{
    public string UserName { get; set; }
    public string Email { get; set; }
}

public class DeleteUserCommand : ICommand<bool>
{
    public string Id { get; set; }
}

Implement handlers for your commands:

public class RegisterUserCommandHandler : ICommandHandler<RegisterUserCommand>
{
    public async Task HandleAsync(RegisterUserCommand command, CancellationToken ct = default)
    {
        // Handle the command
    }
}

public class DeleteUserCommandHandler : ICommandHandler<DeleteUserCommand, bool>
{
    public async Task<bool> HandleAsync(DeleteUserCommand command, CancellationToken ct = default)
    {
        // Handle the command
    }
}

Manually subscribe commands handlers:

var commandBus = new CommandBus();
commandBus.Subscribe(new RegisterUserCommandHandler());
commandBus.Subscribe(new DeleteUserCommandHandler());
await commandBus.ExecuteAsync(new RegisterUserCommand());

Alternatively, use DI for automatic registration in your Program.cs:

services.AddEventSourcing(typeof(RegisterUserCommand));
await new RegisterUserCommand().ExecuteAsync();

Alternatively, register ICommandBus to yor DI container:

services.AddSingleton<ICommandBus, CommandBus>();

Now publish events using the event bus:

var commandBus = serviceProvider.GetRequiredService<ICommandBus>();
await commandBus.ExecuteAsync(new RegisterUserCommand 
{
    UserName = "JohnDoe",
    Email = "john.doe@example.com"
});

Queries Setup

To configure the Queries for executing, follow these steps:

Define your query by implementing the respective interfaces:

public record GetUserQuery(string Id) : IQuery<CustomerEntity>;

Implement handlers for your query:

public sealed class GetUserQueryHandler : IQueryHandler<GetUserQuery, CustomerEntity>
{
    public async Task<CustomerEntity> HandleAsync(GetUserQuery query, CancellationToken ct = default)
    {
        // Handle the query
    }
}

Contributing

I welcome contributions from the community! Please read my contributing guidelines on GitHub to get started.

License

This project is licensed under the MIT License. See the LICENSE file for more information.