From 0497fe180b43e9894f3e456ce2fd7aec1289875b Mon Sep 17 00:00:00 2001
From: Andreas Gehrke <ange@clever.dk>
Date: Mon, 7 Apr 2025 09:39:22 +0200
Subject: [PATCH 1/2] Bring back ProjectionFactory

Also use IServiceScopeFactory instead of IServiceProvider in
ProjectionProcessor to make it more clear that we are only creating scopes
---
 .../EventStoreOptionsBuilderExtensions.cs     |  1 +
 .../ProjectionFactory.cs                      | 40 +++++++++++++++++++
 .../Projections/ProjectionProcessor.cs        | 17 ++++----
 3 files changed, 50 insertions(+), 8 deletions(-)
 create mode 100644 src/Atc.Cosmos.EventStore.Cqrs/ProjectionFactory.cs

diff --git a/src/Atc.Cosmos.EventStore.Cqrs/DependencyInjection/EventStoreOptionsBuilderExtensions.cs b/src/Atc.Cosmos.EventStore.Cqrs/DependencyInjection/EventStoreOptionsBuilderExtensions.cs
index ede23cd..a55fc06 100644
--- a/src/Atc.Cosmos.EventStore.Cqrs/DependencyInjection/EventStoreOptionsBuilderExtensions.cs
+++ b/src/Atc.Cosmos.EventStore.Cqrs/DependencyInjection/EventStoreOptionsBuilderExtensions.cs
@@ -28,6 +28,7 @@ public static EventStoreOptionsBuilder UseCQRS(
         builder.Services.AddSingleton<IProjectionOptionsFactory, ProjectionOptionsFactory>();
 
         builder.Services.AddSingleton(typeof(ProjectionMetadata<>), typeof(ProjectionMetadata<>));
+        builder.Services.AddTransient<IProjectionFactory, DefaultProjectionFactory>();
 
         builder.Services.TryAddSingleton<IProjectionTelemetry, ProjectionTelemetry>();
 
diff --git a/src/Atc.Cosmos.EventStore.Cqrs/ProjectionFactory.cs b/src/Atc.Cosmos.EventStore.Cqrs/ProjectionFactory.cs
new file mode 100644
index 0000000..6ddb384
--- /dev/null
+++ b/src/Atc.Cosmos.EventStore.Cqrs/ProjectionFactory.cs
@@ -0,0 +1,40 @@
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Atc.Cosmos.EventStore.Cqrs;
+
+/// <summary>
+/// Responsible for creating <see cref="IProjection"/> instances.
+/// </summary>
+public interface IProjectionFactory
+{
+    /// <summary>
+    /// Creates a projection of type <typeparamref name="TProjection"/> for the event stream
+    /// identified by <paramref name="streamId"/>.
+    /// </summary>
+    /// <param name="streamId">ID of the stream being projected.</param>
+    /// <param name="cancellationToken">Cancellation.</param>
+    /// <typeparam name="TProjection">Type of projection to create.</typeparam>
+    /// <returns>The created projection.</returns>
+    public Task<IProjection> CreateAsync<TProjection>(EventStreamId streamId, CancellationToken cancellationToken)
+        where TProjection : IProjection;
+}
+
+/// <summary>
+/// The default projection factory which just creates projections by
+/// getting them from the DI-container.
+/// </summary>
+internal sealed class DefaultProjectionFactory : IProjectionFactory
+{
+    private readonly IServiceProvider serviceProvider;
+
+    public DefaultProjectionFactory(IServiceProvider serviceProvider)
+    {
+        this.serviceProvider = serviceProvider;
+    }
+
+    public Task<IProjection> CreateAsync<TProjection>(EventStreamId streamId, CancellationToken cancellationToken)
+        where TProjection : IProjection
+    {
+        return Task.FromResult<IProjection>(serviceProvider.GetRequiredService<TProjection>());
+    }
+}
\ No newline at end of file
diff --git a/src/Atc.Cosmos.EventStore.Cqrs/Projections/ProjectionProcessor.cs b/src/Atc.Cosmos.EventStore.Cqrs/Projections/ProjectionProcessor.cs
index f36e500..cd47aea 100644
--- a/src/Atc.Cosmos.EventStore.Cqrs/Projections/ProjectionProcessor.cs
+++ b/src/Atc.Cosmos.EventStore.Cqrs/Projections/ProjectionProcessor.cs
@@ -10,18 +10,18 @@ internal class ProjectionProcessor<TProjection> : IProjectionProcessor<TProjecti
     private readonly IReadOnlyCollection<ProjectionFilter> filters;
     private readonly IProjectionTelemetry telemetry;
     private readonly ProjectionMetadata<TProjection> projectionMetadata;
-    private readonly IServiceProvider serviceProvider;
+    private readonly IServiceScopeFactory serviceScopeFactory;
     private readonly string projectionName;
 
     public ProjectionProcessor(
         IProjectionOptionsFactory optionsFactory,
         IProjectionTelemetry telemetry,
         ProjectionMetadata<TProjection> projectionMetadata,
-        IServiceProvider serviceProvider)
+        IServiceScopeFactory serviceScopeFactory)
     {
         this.telemetry = telemetry;
         this.projectionMetadata = projectionMetadata;
-        this.serviceProvider = serviceProvider;
+        this.serviceScopeFactory = serviceScopeFactory;
         filters = optionsFactory
             .GetOptions<TProjection>()
             .Filters;
@@ -49,10 +49,6 @@ public async Task<ProjectionAction> ProcessBatchAsync(
 
         foreach (var events in groupedEvents)
         {
-            await using var scope = serviceProvider.CreateAsyncScope();
-
-            var projection = scope.ServiceProvider.GetRequiredService<TProjection>();
-
             using var operation = batchTelemetry.StartProjection(events.Key);
 
             if (!projectionMetadata.CanConsumeOneOrMoreEvents(events))
@@ -62,11 +58,16 @@ public async Task<ProjectionAction> ProcessBatchAsync(
                 continue;
             }
 
+            var eventStreamId = EventStreamId.FromStreamId(events.Key);
+            await using var scope = serviceScopeFactory.CreateAsyncScope();
+            var projectionFactory = scope.ServiceProvider.GetRequiredService<IProjectionFactory>();
+            var projection = await projectionFactory.CreateAsync<TProjection>(eventStreamId, cancellationToken);
+
             try
             {
                 await projection
                     .InitializeAsync(
-                        events.Key,
+                        eventStreamId,
                         cancellationToken)
                     .ConfigureAwait(false);
 

From 43b3bd1a3df9ed320f728b7a8555046a2d14a0a2 Mon Sep 17 00:00:00 2001
From: Andreas Gehrke <ange@clever.dk>
Date: Tue, 8 Apr 2025 10:15:41 +0200
Subject: [PATCH 2/2] Changelog

---
 CHANGELOG.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index fa5832a..91fbccf 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
  registered as transient rather than singleton. This allows `CommandHandler` implementations to use 
  dependencies registered as scoped.
 
+- Reintroduce `IProjectionFactory` in a slightly modified version to allow consumers to make additional "initialization" of projections.
+
 ## [1.17.0] - 2025-03-21
 
 ### Fixed