Allow structs to be used in FlatTableProjection Map statements

src/EventSourcingTests/Bugs/Bug_3643_using_struct_in_map_flattableprojection.cs

@@ -0,0 +1,55 @@
+using System;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Marten.Events.Projections;
+using Marten.Events.Projections.Flattened;
+using Marten.Testing.Harness;
+using Shouldly;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace EventSourcingTests.Bugs;
+
+public class Bug_3643_using_struct_in_map_flattableprojection : BugIntegrationContext{
+    private readonly ITestOutputHelper _output;
+    public Bug_3643_using_struct_in_map_flattableprojection(ITestOutputHelper output)
+    {
+        _output = output;
+    }
+
+    public record MyEvent(Guid Id, MyStruct MyStruct, MyClass MyClass);
+    public record struct MyStruct(string PrimitiveValue);
+    public record MyClass(string PrimitiveValue);
+
+    public class MyTableProjection : FlatTableProjection{
+        public MyTableProjection() : base("my_table_projection", SchemaNameSource.EventSchema){
+            Table.AddColumn<Guid>("id").AsPrimaryKey();
+            Options.TeardownDataOnRebuild = true;
+
+            Project<MyEvent>(map => {
+                map.Map(x => x.MyStruct.PrimitiveValue);
+                map.Map(x => x.MyClass.PrimitiveValue);
+            });
+        }
+    }
+
+
+    [Fact]
+    public async Task add_event_that_requires_mapping_a_struct_and_a_class(){
+        StoreOptions(x => {
+            x.Projections.Add<MyTableProjection>(ProjectionLifecycle.Inline);
+            x.Logger(new TestOutputMartenLogger(_output));
+        });
+
+        await theStore.Storage.ApplyAllConfiguredChangesToDatabaseAsync();
+         using(var session = theStore.LightweightSession()){
+            var e = new MyEvent(Guid.NewGuid(), new MyStruct("StructValue"), null);
+            session.Events.StartStream(Guid.NewGuid(), e);
+            await session.SaveChangesAsync();
+            (string structvalue, string classvalue) result = (await session.AdvancedSql.QueryAsync<string, string>($"SELECT ROW(my_struct_primitive_value), ROW(my_class_primitive_value) FROM bugs.my_table_projection", CancellationToken.None)).First();
+            result.structvalue.ShouldBe("StructValue");
+            result.classvalue.ShouldBeNull();
+        }
+    }
+}

src/Marten/Events/Projections/Flattened/MemberMap.cs

@@ -2,6 +2,7 @@
 using System.Linq;
 using System.Linq.Expressions;
 using System.Reflection;
+using System.Text;
 using JasperFx.CodeGeneration.Model;
 using JasperFx.Core;
 using Marten.Linq.Parsing;
@@ -76,6 +77,17 @@ public string ToInsertExpression(Table table)
 
     public string ToValueAccessorCode(Variable eventVariable)
     {
-        return $"{eventVariable.Usage}.Data.{_members.Select(x => x.Name).Join("?.")}";
+        var accessor = new StringBuilder();
+        for(var i = 0; i < _members.Length; i++){
+            accessor.Append(_members[i].Name);
+            if(i < _members.Length - 1){
+                if(_members[i] is PropertyInfo propertyinfo && propertyinfo.PropertyType.IsValueType && !propertyinfo.PropertyType.IsPrimitive){
+                    accessor.Append('.');
+                }else{
+                    accessor.Append("?.");
+                }
+            }
+        }
+        return $"{eventVariable.Usage}.Data.{accessor}";
     }
 }