Allow customization of the snapshot projection

src/EventSourcingTests/Projections/inline_aggregation_with_custom_projection_configuration.cs

@@ -0,0 +1,24 @@
+using System;
+using Marten.Events.Aggregation;
+using Marten.Events.Projections;
+using Marten.Testing.Harness;
+using NSubstitute;
+using Xunit;
+
+namespace EventSourcingTests.Projections;
+
+public class inline_aggregation_with_custom_projection_configuration : OneOffConfigurationsContext
+{
+    [Fact]
+    public void does_call_custom_projection_configuration()
+    {
+        var configureProjection = Substitute.For<Action<SingleStreamProjection<QuestParty>>>();
+
+        StoreOptions(_ =>
+        {
+            _.Projections.Snapshot<QuestParty>(SnapshotLifecycle.Inline, configureProjection);
+        });
+
+        configureProjection.Received(1).Invoke(Arg.Any<SingleStreamProjection<QuestParty>>());
+    }
+}

src/Marten/Events/Projections/ProjectionOptions.cs

@@ -175,7 +175,7 @@ public MartenRegistry.DocumentMappingExpression<T> LiveStreamAggregation<T>(
         Action<AsyncOptions> asyncConfiguration = null
     )
     {
-        var expression = singleStreamProjection<T>(ProjectionLifecycle.Live, asyncConfiguration);
+        var expression = singleStreamProjection<T>(ProjectionLifecycle.Live, null, asyncConfiguration);
 
         // Hack to address https://github.com/JasperFx/marten/issues/2610
         _options.Storage.MappingFor(typeof(T)).SkipSchemaGeneration = true;
@@ -190,17 +190,36 @@ public MartenRegistry.DocumentMappingExpression<T> LiveStreamAggregation<T>(
     /// <param name="lifecycle">Override the snapshot lifecycle. The default is Inline</param>
     /// <param name="asyncConfiguration">
     ///     Optional configuration including teardown instructions for the usage of this
-    ///     projection within the async projection daempon
+    ///     projection within the async projection daemon
+    /// </param>
+    /// <returns>The extended storage configuration for document T</returns>
+    public MartenRegistry.DocumentMappingExpression<T> Snapshot<T>(
+        SnapshotLifecycle lifecycle,
+        Action<AsyncOptions> asyncConfiguration = null
+    ) =>
+        singleStreamProjection<T>(lifecycle.Map(), null, asyncConfiguration);
+
+    /// <summary>
+    /// Perform automated snapshot on each event for selected entity type
+    /// </summary>
+    /// <typeparam name="T"></typeparam>
+    /// <param name="lifecycle">Override the snapshot lifecycle. The default is Inline</param>
+    /// <param name="configureProjection">Use it to further customize the projection.</param>
+    /// <param name="asyncConfiguration">
+    ///     Optional configuration including teardown instructions for the usage of this
+    ///     projection within the async projection daemon
     /// </param>
     /// <returns>The extended storage configuration for document T</returns>
     public MartenRegistry.DocumentMappingExpression<T> Snapshot<T>(
         SnapshotLifecycle lifecycle,
+        Action<SingleStreamProjection<T>> configureProjection,
         Action<AsyncOptions> asyncConfiguration = null
     ) =>
-        singleStreamProjection<T>(lifecycle.Map(), asyncConfiguration);
+        singleStreamProjection<T>(lifecycle.Map(), configureProjection, asyncConfiguration);
 
     private MartenRegistry.DocumentMappingExpression<T> singleStreamProjection<T>(
         ProjectionLifecycle lifecycle,
+        Action<SingleStreamProjection<T>> configureProjection = null,
         Action<AsyncOptions> asyncConfiguration = null
     )
     {
@@ -209,6 +228,8 @@ private MartenRegistry.DocumentMappingExpression<T> singleStreamProjection<T>(
 
         var source = new SingleStreamProjection<T> { Lifecycle = lifecycle };
 
+        configureProjection?.Invoke(source);
+
         asyncConfiguration?.Invoke(source.Options);
 
         source.AssembleAndAssertValidity();