Ability to build a proper event wrapper from DocumentSession.Events

Directory.Build.props

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project>
     <PropertyGroup>
-        <Version>8.8.2</Version>
+        <Version>8.9.0</Version>
         <LangVersion>12.0</LangVersion>
         <Authors>Jeremy D. Miller;Babu Annamalai;Jaedyn Tonee</Authors>
         <PackageIconUrl>https://martendb.io/logo.png</PackageIconUrl>

src/EventSourcingTests/Metadata/overriding_metadata_on_appends.cs

@@ -248,6 +248,31 @@ public async Task set_header_on_individual_events(EventAppendMode mode)
         events[2].Headers["color"].ShouldBe("green");
     }
 
+    [Theory]
+    [InlineData(JasperFx.Events.EventAppendMode.Rich)]
+    [InlineData(JasperFx.Events.EventAppendMode.QuickWithServerTimestamps)]
+    public async Task override_header_on_event_with_as_type_then_get_header_but_declared_as_object(EventAppendMode mode)
+    {
+        EventAppendMode = mode;
+        var streamId = Guid.NewGuid();
+
+        var action = theSession.Events.StartStream(streamId, new AEvent(), new BEvent(), new CEvent());
+        action.Events[0].SetHeader("color", "red");
+        action.Events[1].SetHeader("color", "blue");
+        action.Events[2].SetHeader("color", "green");
+
+        await theSession.SaveChangesAsync();
+
+        object data = new AEvent();
+        var withHeader = theSession.Events.BuildEvent(data).WithHeader("color", "orange");
+        withHeader.ShouldBeOfType<Event<AEvent>>();
+        theSession.Events.Append(streamId, withHeader);
+        await theSession.SaveChangesAsync();
+
+        var events = await theSession.Events.FetchStreamAsync(streamId);
+        events.Last().Headers["color"].ShouldBe("orange");
+    }
+
     /* TODO
      Do this w/ FetchForWriting where you pass in Event<T> on new and old, quick and rich
      Append by passing in Event<T>

src/Marten/Events/EventStore.cs

@@ -20,6 +20,12 @@ public EventStore(DocumentSessionBase session, DocumentStore store, Tenant tenan
         _store = store;
     }
 
+    public IEvent BuildEvent(object data)
+    {
+        if (data == null) throw new ArgumentNullException(nameof(data));
+        return _store.Events.BuildEvent(data);
+    }
+
     public void OverwriteEvent(IEvent e)
     {
         var op = new OverwriteEventOperation(_store.Events, e);

src/Marten/Events/IEventStoreOperations.cs

@@ -10,6 +10,14 @@ namespace Marten.Events;
 
 public interface IEventStoreOperations: IEventOperations, IQueryEventStore
 {
+    /// <summary>
+    /// Helper to create an event wrapper as part of appending events if you need
+    /// to express custom metadata
+    /// </summary>
+    /// <param name="data"></param>
+    /// <returns></returns>
+    IEvent BuildEvent(object data);
+
     /// <summary>
     ///     Append one or more events in order to an existing stream and verify that maximum event id for the stream
     ///     matches supplied expected version or transaction is aborted.