This is an experiment. Don't use it in a production system.

ArbitR

A simple light weight CQRS implementation built in .NET

Has support for Commands, Queries and Event notifications.

ArbitR is built on top of the .NET Service Collection, after configuration inject an IArbiter where you need it and you are good to go!

Configuration

Within a C# .NET 5 Web Applications Startup.cs or the project that contains the write/read services, read model managers & workflows.

public void ConfigureServices(IServiceCollection services)
{
    //...
    services.AddArbitR(Assembly.GetExecutingAssembly());
    //...
}

Usage

There are 4 types of services available in ArbitR.

1. WriteService
2. ReadService
3. ReadModelManager
4. Workflow (Beta)

This architecture is based off my interpretation of the Microsoft docs found here:

https://docs.microsoft.com/en-us/azure/architecture/patterns/cqrs

WriteService

Used for managing a single tables Create/Remove/Update actions. This is done through the invocation of commands. When making a command inherit ICommand.

Sample

public class ExampleWriteService : WriteService,
    IHandleCommand<ExampleCommand>
{
    /// ...
    
    public void Handle(ExampleCommand cmd)
    {
        // ...
    }
}

ReadService

Used for managing a single tables Display actions. This is done through the invocation of queries. When making a query inherit IQuery.

Sample

public class ExampleReadService : ReadService,
    IHandleQuery<ExampleQuery, ExampleModel>
{
    /// ...
    
    public ExampleModel Handle(ExampleQuery query)
    {
        // ...
    }
}

ReadModelManager

Used for managing read-only views built from one or more tables. This is done through the raising of events. When making an event, inherit IEvent.

Sample

public class LoginAttemptReadModelManager : ReadModelManager,
    IHandleEvent<LoginSuccessEvent>,
    IHandleEvent<LoginFailedEvent>,
    IHandleQuery<GetLoginAttempts, IEnumerable<LoginAttempt>>
{
    public void Handle(LoginSuccessEvent eEvent)
    {
        // Save login attempt
    }

    public void Handle(LoginFailedEvent eEvent)
    {
        // Save login attempt
    }
    
    public IEnumerable<LoginAttempt> Handle(GetLoginAttempts query)
    {
        // Get Login Attempts
    }
}

Workflow (Beta)

A workflow is meant to be an elegant way of describing a process for which Arbiter will then handle its orchestration. Use it when you need to chain together multiple commands, queries & events in a sequential order. When making a workflow, inherit Workflow<T> where T is the returned result upon success of the workflow.

Sample

public class RegisterUserWorkflow : Workflow<UserRegisteredResult>
{
    private User _user = default!;
    
    public RegisterUserWorkflow(string email, string password, string firstname, string surname)
    {
        AddStep(() => new CreateUserCommand{Email = email, Password = password, Firstname = firstname, Surname = surname})
            .OnSuccess(() => new UserCreatedEvent(email));

        AddStep(() => AuthenticateUser(email))
            .OnSuccess(() => new UserAuthenticatedEvent(firstname))
            .OnFailure(() => new UserFailedAuthenticationEvent($"{email} failed Authentication!"))
            .OnFailureThrow(e => new FailedAuthException(e));
    }
    
    public ICommand AuthenticateUser(string email)
    {
        _user = _arbiter.Invoke(new GetUserQuery(email));
        return new AuthenticateUserCommand
        {
            Email = _user.Email,
            Password = _user.Password
        };
    }
    
    public override UserRegisteredResult GetResult()
    {
        return new UserRegisteredResult(_user);
    }
}