#2941 Tests for: Using Explicit Code for Marten live aggregate projections

src/EventSourcingTests/Aggregation/livestream_aggregates_can_be_explicit.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Marten.Events.Aggregation;
+using Marten.Events.Projections;
+using Marten.Internal.Sessions;
+using Marten.Testing.Harness;
+using Shouldly;
+using Xunit;
+
+namespace EventSourcingTests.Aggregation;
+
+public class livestream_aggregates_can_be_explicit: OneOffConfigurationsContext
+{
+    [Fact]
+    public void livestream_aggregate_projections_should_also_be_allowed_to_be_explicit()
+    {
+        var store = StoreOptions(opts =>
+        {
+            opts.Projections.Add(new PatientProjection(), ProjectionLifecycle.Live);
+        });
+
+        theStore.StorageFeatures.AllDocumentMappings.Select(x => x.DocumentType)
+            .ShouldContain(typeof(Patient));
+    }
+
+    [Fact]
+    public async Task explicit_livestream_aggregate_Can_Be_Created()
+    {
+        var store = StoreOptions(opts =>
+        {
+            opts.Projections.Add(new PatientProjection(), ProjectionLifecycle.Live);
+        });
+        var patientId = Guid.NewGuid();
+        var patientRegistered = new PatientRegistered(
+            PatientId: Guid.NewGuid(),
+            Name: "John Doe",
+            DateOfBirth: new(1980, 5, 20));
+
+        var appointmentScheduled = new AppointmentScheduled(
+            AppointmentId: Guid.NewGuid(),
+            PatientId: patientRegistered.PatientId,
+            AppointmentDate: DateTime.Now.AddDays(7)); // Schedule an appointment for 7 days from now
+
+        var treatmentAdministered = new TreatmentAdministered(
+            TreatmentId: Guid.NewGuid(),
+            PatientId: patientRegistered.PatientId,
+            TreatmentDescription: "Routine Checkup",
+            TreatmentDate: appointmentScheduled.AppointmentDate.AddHours(1)); // Assume the treatment is an hour after the appointment
+
+        var patientDischarged = new PatientDischarged(
+            PatientId: patientRegistered.PatientId,
+            DischargeDate: treatmentAdministered.TreatmentDate.AddDays(1)); // Discharged the day after treatment
+
+        await using var session = store.LightweightSession();
+        session.Events.StartStream<Patient>(patientId, patientRegistered, appointmentScheduled, treatmentAdministered, patientDischarged);
+        await session.SaveChangesAsync();
+
+        var patient = await session.Events.AggregateStreamAsync<Patient>(patientId);
+        patient.ShouldNotBeNull();
+        patient.Name.ShouldBe("John Doe");
+        patient.DateOfBirth.ShouldBe(new(1980, 5, 20));
+        patient.Appointments.Count.ShouldBe(1);
+        patient.Appointments[0].AppointmentDate.ShouldBe(appointmentScheduled.AppointmentDate);
+        patient.Treatments.Count.ShouldBe(1);
+        patient.Treatments[0].Description.ShouldBe("Routine Checkup");
+        patient.Treatments[0].TreatmentDate.ShouldBe(treatmentAdministered.TreatmentDate);
+        patient.DischargeDate.ShouldBe(patientDischarged.DischargeDate);
+    }
+
+    public class PatientProjection: CustomProjection<Patient, Guid>
+    {
+        public PatientProjection()
+        {
+            // Define how to group events into aggregates by stream ID
+            Slicer = new ByStreamId<Patient>();
+
+            // Optimize event filtering for the async daemon
+            IncludeType<PatientRegistered>();
+            IncludeType<AppointmentScheduled>();
+            IncludeType<TreatmentAdministered>();
+            IncludeType<PatientDischarged>();
+        }
+
+        public override ValueTask ApplyChangesAsync(DocumentSessionBase session, EventSlice<Patient, Guid> slice, CancellationToken cancellation, ProjectionLifecycle lifecycle = ProjectionLifecycle.Inline)
+        {
+            var aggregate = slice.Aggregate;
+
+            foreach (var e in slice.AllData())
+            {
+                aggregate = e switch
+                {
+                    PatientRegistered registered => Patient.Create(registered),
+                    AppointmentScheduled scheduled => Patient.Apply(aggregate, scheduled),
+                    TreatmentAdministered administered => Patient.Apply(aggregate, administered),
+                    PatientDischarged discharged => Patient.Apply(aggregate, discharged),
+                    _ => aggregate
+                };
+            }
+
+            if (aggregate is { })
+            {
+                session.Store(aggregate);
+            }
+
+            return new();
+        }
+    }
+
+
+    public record PatientRegistered(Guid PatientId, string Name, DateTime DateOfBirth);
+    public record AppointmentScheduled(Guid AppointmentId, Guid PatientId, DateTime AppointmentDate);
+    public record TreatmentAdministered(Guid TreatmentId, Guid PatientId, string TreatmentDescription, DateTime TreatmentDate);
+    public record PatientDischarged(Guid PatientId, DateTime DischargeDate);
+
+    public record Patient(
+        Guid PatientId,
+        string Name,
+        DateTime DateOfBirth,
+        List<Appointment> Appointments,
+        List<Treatment> Treatments,
+        DateTime? DischargeDate)
+    {
+
+        public static Patient Create(PatientRegistered @event) =>
+            new(@event.PatientId, @event.Name, @event.DateOfBirth, [], [], null);
+
+        public static Patient Apply(Patient state, AppointmentScheduled @event) =>
+            state with
+            {
+                Appointments = [.. state.Appointments, new(@event.AppointmentId, @event.AppointmentDate)]
+            };
+
+        public static Patient Apply(Patient state, TreatmentAdministered @event) =>
+            state with
+            {
+                Treatments = [.. state.Treatments, new(@event.TreatmentId, @event.TreatmentDescription, @event.TreatmentDate)]
+            };
+
+        public static Patient Apply(Patient state, PatientDischarged @event) =>
+            state with
+            {
+                DischargeDate = @event.DischargeDate
+            };
+    }
+
+    public record Appointment(Guid AppointmentId, DateTime AppointmentDate);
+
+    public record Treatment(Guid TreatmentId, string Description, DateTime TreatmentDate);
+}