Fix ProjectionVersion suffix being overwritten by explicit DocumentAlias

src/EventSourcingTests/Aggregation/blue_green_deployment_of_aggregates.cs

@@ -38,6 +38,20 @@ public void apply_the_version_suffix_to_table_alias_when_version_attribute_is_on
         var mapping = store.Options.Storage.MappingFor(typeof(OtherAggregate));
         mapping.Alias.ShouldBe("otheraggregate_3");
     }
+
+    [Fact]
+    public void apply_the_version_suffix_when_document_alias_is_set_via_fluent_api()
+    {
+        using var store = DocumentStore.For(opts =>
+        {
+            opts.Connection(ConnectionSource.ConnectionString);
+            opts.Projections.Add<Version2>(ProjectionLifecycle.Async);
+            opts.Schema.For<MyAggregate>().DocumentAlias("custom_alias");
+        });
+
+        var mapping = store.Options.Storage.MappingFor(typeof(MyAggregate));
+        mapping.Alias.ShouldBe("custom_alias_2");
+    }
 }
 
 public class Version2: SingleStreamProjection<MyAggregate, Guid>

src/Marten/Events/Projections/ProjectionDocumentPolicy.cs

@@ -14,11 +14,6 @@ public void Apply(DocumentMapping mapping)
 
         if (mapping.StoreOptions.Projections.TryFindAggregate(mapping.DocumentType, out var projection))
         {
-            if (projection.Version > 1)
-            {
-                mapping.Alias += "_" + projection.Version;
-            }
-
             mapping.UseOptimisticConcurrency = false;
             mapping.Metadata.Version.Enabled = false;
             mapping.UseNumericRevisions = true;
@@ -28,7 +23,26 @@ public void Apply(DocumentMapping mapping)
             {
                 m.ConfigureAggregateMapping(mapping, mapping.StoreOptions);
             }
+        }
+    }
+}
 
+internal class ProjectionVersionAliasPolicy : IDocumentPolicy
+{
+    public void Apply(DocumentMapping mapping)
+    {
+        if (mapping.StoreOptions.Projections == null) return;
+
+        if (mapping.StoreOptions.Projections.TryFindAggregate(mapping.DocumentType, out var projection))
+        {
+            if (projection.Version > 1)
+            {
+                var suffix = "_" + projection.Version;
+                if (!mapping.Alias.EndsWith(suffix))
+                {
+                    mapping.Alias += suffix;
+                }
+            }
         }
     }
 }

src/Marten/StoreOptions.cs

@@ -72,7 +72,7 @@ internal INpgsqlDataSourceFactory NpgsqlDataSourceFactory
         new ProjectionDocumentPolicy()
     ];
 
-    private readonly List<IDocumentPolicy> _postPolicies = new();
+    private readonly List<IDocumentPolicy> _postPolicies = new() { new ProjectionVersionAliasPolicy() };
 
     /// <summary>
     ///     Register "initial data loads" that will be applied to the DocumentStore when it is