HerrGeneral.Core 0.1.8-rc

Herr General

Herr General is a Cqrs implementation with built in debug log for simple modular monolith. (strongly inspired from MediatR)

Implementation choice

One storage for all pro : no eventual consistency cons : no eventual consistency ⇒ doesn't scale

One transaction by command.

ReadModel as singleton.

All ids are System.Guid.

Result pattern but CreationResult return the id of the created object.

Installing Herr General with NuGet

Write side HerrGeneral.WriteSide or HerrGeneral.WriteSide.DDD

Read side HerrGeneral.ReadSide

Application or infrastructure layer HerrGeneral.Core

Registering with IServiceCollection

Herr General supports Microsoft.Extensions.DependencyInjection.Abstractions directly. To register write side commands and eventHandlers and read side eventHandlers:

services.UseHerrGeneral(scanner =>
        scanner
            .OnWriteSide(typeof(Person).Assembly, typeof(Person).Namespace!)
            .OnReadSide(typeof(PersonFriendRM).Assembly, typeof(PersonFriendRM).Namespace!));

Sample code

// Write Side
public record SetFriend : ChangeAggregate<Person>
{
    private readonly string _friend;

    public SetFriend(Guid aggregateId, string friend) : base(aggregateId) => _friend = friend;

    public class Handler : ChangeAggregateHandler<Person,SetFriend>
    {
        public Handler(CtorParams ctorParams) : base(ctorParams) { }

        protected override Person Handle(Person aggregate, SetFriend command) => 
            aggregate.SetFriend(command._friend, command.Id);
    }
}

// Read side
public record PersonFriendRM(Guid PersonId, string Person, string Friend)
{
    public class PersonFriendRMRepository : IEventHandler<FriendChanged>
    {
        private readonly Dictionary<Guid, PersonFriendRM> _personFriends = new();
        public Task Handle(FriendChanged notification, CancellationToken cancellationToken)
        {
            _personFriends[notification.AggregateId] = new PersonFriendRM(notification.AggregateId, notification.Person, notification.FriendName);
            return Task.CompletedTask;
        }

        public PersonFriendRM Get(Guid personId) => _personFriends[personId];
    }    
}

Debug logger output sample

←------------------ SetFriend <46a0deab-0485-403e-821a-834a96517a7c> thread<1> -------------------> || Publish Write Side on thread<1> HerrGeneral.SampleApplication.WriteSide.FriendChanged

|| Publish Read Side (1 event) on thread<1> HerrGeneral.SampleApplication.WriteSide.FriendChanged → Handle by HerrGeneral.SampleApplication.ReadSide.PersonFriendRM+PersonFriendRMRepository ←------------------ SetFriend Finished 00:00:00.0021475 -------------------/>

How it works

A user: Hey, I want to change my friend name. Application: Ok, give me the command and I will take care of the rest. I'll send you back a commandResult when I'm done.

In the application black box : Mediator: Anybody to handle this command ? CommandHandler: I"m here. CommandHandler: I'm done and I have some events to publish. WriteSideEventPublisher: That's my job. WriteSideEventPublisher: Anybody to handle this event on the write side ? (for each event). WriteSideEventHandler: Me (and I may have other events to publish). WriteSideEventPublisher: I'm done. CommandHandler: Thank you, now I can transmit all those events to the read side. ReadSideEventPublisher: Anybody to handle this event on the read side ? (for each event). ReadModel: Yes me. ReadSideEventPublisher: I'm done. CommandHandler: I'm done.

Application: Here is your command result.

Result pattern

ChangeResult

Herr general return ChangeResult for ChangeCommand 3 states : Success, DomainError, PanicException

updateResult.Match(() =>
    {
        ...
    },
    error => ...,
    exception => ...);

CreationResult

Herr general return CreationResult for CreationCommand 3 states : Success<Guid>, DomainError, PanicException

creationResult.Match(id =>
    {
        ...
    },
    error => ...,
    exception => ...);