Event Store¶

using Deepstaging.EventStore;
using Deepstaging.Ids;

// 1. Define a stream identity
[TypedId]
[StreamId]
public readonly partial struct OrderId;

// 2. Define events
public sealed record OrderCreated(OrderId OrderId, string CustomerName) : IAggregateEvent;
public sealed record OrderItemAdded(string Sku, int Quantity) : IAggregateEvent;
public sealed record OrderCompleted : IAggregateEvent;

// 3. Define the aggregate
[EventSourcedAggregate]
public partial record Order(OrderId Id, string CustomerName, int ItemCount, bool IsCompleted)
{
    public static Order Create(OrderCreated e) =>
        new(e.OrderId, e.CustomerName, 0, false);

    public Order Apply(OrderItemAdded e) =>
        this with { ItemCount = ItemCount + e.Quantity };

    public Order Apply(OrderCompleted _) =>
        this with { IsCompleted = true };
}

// 4. Declare the event store container
[EventStore]
public static partial class AppEventStore;

// 5. Use the generated Eff<RT, T> effect methods
var program =
    from id in AppEventStore.Orders.StartStream<AppRuntime>(
        new OrderCreated(OrderId.New(), "Alice"))
    from stream in AppEventStore.Orders.FetchForWriting<AppRuntime>(id)
    from order in stream.Append<AppRuntime>(new OrderItemAdded("SKU-001", 3))
                  >> AppEventStore.Commit<AppRuntime>()
                  >> AppEventStore.Orders.Aggregate<AppRuntime>(id)
    select order;