Eventually

An Event sourcing framework used by Scribbly.Fun free for use and contributions.

🏃‍♂️ Aggregate

Aggregates are the thing, yup the thing your commands and events effect. Aggregates should extend the Aggregate abstract class.

Aggregates should include an apply method for each type of event it's expected to receive.

class Box: Aggregate
{
    public Capacity? Capacity { get; private set; }
    public Shipping_label? Shipping_label { get; private set; }
    public List<Bottle> Contents { get; } = new();
    public bool Closed { get; private set; }
    public bool Shipped { get; private set; }

    public void Apply(Box_created @event)
    {
        Capacity = @event.Capacity;
    }

    public void Apply(Beer_added @event)
    {
        Contents.Add(@event.Beer);
    }
    
    public void Apply(Label_applied @event)
    {
        Shipping_label = @event.Label;
    }

    public void Apply(Box_shipped @event)
    {
        Shipped = true;
    }
}

💪 Commands

Commands command the system to act on an aggregate. A command must implement the ICommand interface

public record ShipBox : ICommand;

🛒 Handlers

A handle accepts the command and applies business logic. Command handlers should extend the CommandHandler<TCommand, TAggregate> base class.

A handlers purpose is to encapsulate all the business logic.

internal class ShipBoxHandler(
    IEnumerable<IEvent> eventStream,
    Action<IEvent> publishEvent)
    : CommandHandler<Ship_box, Box>(eventStream, publishEvent)
{
    protected override IEnumerable<IEvent> HandleCommand(
        Box aggregate,
        Ship_box command)
    {
        if (aggregate is { Closed: true, Shipping_label: not null })
        {
            yield return new Box_shipped();
            yield break;
        }

        if (!aggregate.Closed)
            yield return new Box_was_not_ready(
                Box_was_not_ready.Fail_reason.Box_was_not_closed);

        if (aggregate.Shipping_label is null)
            yield return new Box_was_not_ready(
                Box_was_not_ready.Fail_reason.Box_has_no_shipping_label);
    }
}

📆 Events

A event is the result of the applied command. An event must implement the IEvent interface

public record BoxShipped : IEvent;

public record BoxNotReadyToShip(Reason Reason) : IEvent;