Doodad

Doodad is an opinionated DDD and CQRS framework for .NET.

Work is based largely off of Microsoft's guide Tackling Business Complexity in a Microservice with DDD and CQRS Patterns and patterns used in the eShopOnContainers Ordering Service, with a little added flavour.

Doodad

The DDD package contains the common base classes and interfaces referred to as the 'seedwork'. This term is used because it's usually just a small set of classes and tends to be copied and pasted between projects, but in this case, the aim is to provide a more formal structure.

• IEntity: An object defined by its identity.
• IAggregateRoot: The root object of an aggregate; a collection of objects treated as one unit.
• IDomainEvent: Something that happened that is of interest to domain experts.
• ValueObject: An immutable object defined by its values, without a concept of identity.
• Enumeration: A set of possible named values.
• Singleton: A unit type that only allows one value.
• IRepository: Retreives an aggregate from a storage.

public class Person : Entity, IAggregateRoot
{
    public string Name { get; set; }
}

Maths

ValueObjects can often be mathematical values. The package provides ways to remove boilerplate when implementing C# operators to add, subtract, multiply and divide these values.

• IProduct: A value derived from multiplying two factors.
• IQuotient: A value derived from dividing a dividend by a divisor.

public class Force : ProductValueObject<Force, double, Mass, Acceleration>
{
    public Force(double value) : base(value) { }

    protected override IEnumerable<object> GetValues()
    {
        yield return Value;
    }
}

Doodad.Cqrs

The CQRS package brings in a dependency on MediatR and defines interfaces to better separate commands and queries.

• ICommand: Changes the state of a system but does not return a value.
• IQuery: Returns results and does not change the state of the system.
• IEvent: Something that has happened in the system.

public class DoTheThingCommandHandler : ICommandHandler<DoThingCommand>
{
    public Task<CommandResult> Handle(DoThingCommand command)
    {
    }
}

Subscriber

MediatR notification handlers are their own classes, but sometimes we want a way to subscribe and unsubscribe at runtime.

• IMediatorSubscriber: Allows subscribing to an event at runtime.

internal class WorkMonitor
{
    public WorkMonitor(IMediatorSubscriber subscriber)
    {
        subscriber.Subscribe<WorkDoneEvent>(HandleWorkDone);
    }

    private Task HandleWorkDone(WorkDoneEvent workDoneEvent)
    {
    }
}