updated events to records, some renaming and restructuring

StudentEnrollmentConsoleApp/Events/Event.cs

@@ -1,8 +1,6 @@
 namespace StudentEnrollmentConsoleApp.Events;
 
-public abstract class Event
+public abstract record Event
 {
-    public abstract string StreamId { get; }
-
-    public DateTime CreatedAtUtc { get; set; }
+    public string Id { get; init; } = default!;
 }

StudentEnrollmentConsoleApp/Events/EventTypeMapper.cs

@@ -0,0 +1,35 @@
+using System.Collections.Concurrent;
+
+namespace StudentEnrollmentConsoleApp.Events;
+
+public class EventTypeMapper
+{
+    public static readonly EventTypeMapper Instance = new();
+
+    private readonly ConcurrentDictionary<string, Type?> _typeMap = new();
+    private readonly ConcurrentDictionary<Type, string> _typeNameMap = new();
+
+    public string ToName<TEventType>() => ToName(typeof(TEventType));
+
+    public string ToName(Type eventType) => _typeNameMap.GetOrAdd(eventType, _ =>
+    {
+        var eventTypeName = eventType.FullName!;
+        _typeMap.TryAdd(eventTypeName, eventType);
+        return eventTypeName;
+    });
+
+    public Type? ToType(string eventTypeName) => _typeMap.GetOrAdd(eventTypeName, _ =>
+    {
+        var type = AppDomain.CurrentDomain
+            .GetAssemblies()
+            .SelectMany(a => a.GetTypes().Where(x => x.FullName == eventTypeName || x.Name == eventTypeName))
+            .FirstOrDefault();
+
+        if (type == null)
+            return null;
+
+        _typeNameMap.TryAdd(type, eventTypeName);
+
+        return type;
+    });
+}

StudentEnrollmentConsoleApp/Events/StudentCreated.cs

@@ -1,11 +1,9 @@
 namespace StudentEnrollmentConsoleApp.Events;
 
-public class StudentCreated : Event
+public record StudentCreated : Event
 {
-    public required string StudentId { get; init; }
     public required string FullName { get; init; }
     public required string Email { get; init; }
     public required DateTime DateOfBirth { get; init; }
-
-    public override string StreamId => StudentId;
+    public DateTime CreatedAtUtc { get; init; }
 }

StudentEnrollmentConsoleApp/Events/StudentEmailChanged.cs

@@ -0,0 +1,7 @@
+namespace StudentEnrollmentConsoleApp.Events;
+
+public record StudentEmailChanged : Event
+{
+    public required string Email { get; init; }
+    public DateTime ChangedAtUtc { get; init; }
+}

StudentEnrollmentConsoleApp/Events/StudentEnrolled.cs

@@ -1,9 +1,7 @@
 namespace StudentEnrollmentConsoleApp.Events;
 
-public class StudentEnrolled : Event
+public record StudentEnrolled : Event
 {
-    public required string StudentId { get; init; }
     public required string CourseName { get; init; }
-
-    public override string StreamId => StudentId;
+    public DateTime EnrolledAtUtc { get; init; }
 }

StudentEnrollmentConsoleApp/Events/StudentWithdrawn.cs

@@ -0,0 +1,7 @@
+namespace StudentEnrollmentConsoleApp.Events;
+
+public record StudentWithdrawn : Event
+{
+    public required string CourseName { get; init; }
+    public DateTime WithdrawnAtUtc { get; init; }
+}

StudentEnrollmentConsoleApp/Program.cs

@@ -3,6 +3,12 @@
 using EventStore.Client;
 using StudentEnrollmentConsoleApp.Events;
 
+// Register events to a singleton for ease-of-reference
+EventTypeMapper.Instance.ToName(typeof(StudentCreated));
+EventTypeMapper.Instance.ToName(typeof(StudentEnrolled));
+EventTypeMapper.Instance.ToName(typeof(StudentWithdrawn));
+EventTypeMapper.Instance.ToName(typeof(StudentEmailChanged));
+
 var id = Guid.Parse("a662d446-4920-415e-8c2a-0dd4a6c58908");
 var streamId = $"student-{id}";
 
@@ -11,10 +17,11 @@
     "StudentCreated",
     JsonSerializer.SerializeToUtf8Bytes(new StudentCreated
     {
-        StudentId = streamId,
+        Id = streamId,
         FullName = "Erik Shafer",
         Email = "[email protected]",
-        DateOfBirth = new DateTime(1987, 1, 1)
+        DateOfBirth = new DateTime(1987, 1, 1),
+        CreatedAtUtc = DateTime.UtcNow
     })
 );
 
@@ -23,19 +30,20 @@
     "StudentEnrolled",
     JsonSerializer.SerializeToUtf8Bytes(new StudentEnrolled
     {
-        StudentId = streamId,
-        CourseName = "From Zero to Hero: REST APis in .NET"
+        Id = streamId,
+        CourseName = "From Zero to Hero: REST APis in .NET",
+        EnrolledAtUtc = DateTime.UtcNow
     })
 );
 
-var updated = new EventData(
+var emailChanged = new EventData(
     Uuid.NewUuid(),
-    "StudentUpdated", 
-    JsonSerializer.SerializeToUtf8Bytes(new StudentUpdated
+    "StudentEmailChanged",
+    JsonSerializer.SerializeToUtf8Bytes(new StudentEmailChanged
     {
-        StudentId = streamId,
-        FullName = "Erik Shafer",
-        Email = "[email protected]",
+        Id = streamId,
+        Email = "[email protected]",
+        ChangedAtUtc = DateTime.UtcNow
     })
 );
 
@@ -48,7 +56,7 @@
 await client.AppendToStreamAsync(
     streamId,
     StreamState.Any,
-    new[] { created, enrolled, updated },
+    new[] { created, enrolled, emailChanged },
     cancellationToken: default
 );
 
@@ -62,21 +70,38 @@ await client.AppendToStreamAsync(
 var eventStream = await readStreamResult.ToListAsync();
 
 // Write out the events from the stream
-foreach (var @event in eventStream)
+Console.WriteLine("Events from selected stream: ");
+foreach (var resolved in eventStream)
 {
-    Console.WriteLine($"EventId: {@event.Event.EventId}");
-    Console.WriteLine($"EventStreamId: {@event.Event.EventStreamId}");
-    Console.WriteLine($"EventType: {@event.Event.EventType}");
-    Console.WriteLine($"Data: {Encoding.UTF8.GetString(@event.Event.Data.ToArray())}");
-    Console.WriteLine("---");
+    Console.WriteLine($"\tEventId: {resolved.Event.EventId}");
+    Console.WriteLine($"\tEventStreamId: {resolved.Event.EventStreamId}");
+    Console.WriteLine($"\tEventType: {resolved.Event.EventType}");
+    Console.WriteLine($"\tData: {Encoding.UTF8.GetString(resolved.Event.Data.ToArray())}");
+    Console.WriteLine("");
 }
 
 // Write out all the courses the student enrolled in
 var enrolledCourses = eventStream
     .Where(re => re.Event.EventType == "StudentEnrolled")
     .Select(re => JsonSerializer.Deserialize<StudentEnrolled>(re.Event.Data.ToArray()))
     .Select(se => se!.CourseName)
-    .ToArray();
+    .ToList();
+Console.WriteLine("Courses enrolled in: ");
+enrolledCourses.ForEach(ec => Console.WriteLine($"\t- {ec}"));
+Console.WriteLine("");
+
+// Write out using the mapper
+Console.WriteLine("Deserialized events:");
+foreach (var resolved in eventStream)
+{
+    var eventType = EventTypeMapper.Instance.ToType(resolved.Event.EventType);
+
+    if (eventType == null)
+        break;
+
+    var deserializedEvent = JsonSerializer.Deserialize(Encoding.UTF8.GetString(resolved.Event.Data.Span), eventType);
+
+    Console.WriteLine($"\t{deserializedEvent}");
+}
 
-Console.WriteLine($"Courses enrolled in: {enrolledCourses}");
 Console.WriteLine("");

StudentEnrollmentConsoleApp/Student.cs

@@ -4,11 +4,12 @@ namespace StudentEnrollmentConsoleApp;
 
 public class Student
 {
-    public string Id { get; set; }
-    public string FullName { get; set; }
-    public string Email { get; set; }
+    public string Id { get; set; } = default!;
+    public string FullName { get; set; } = default!;
+    public string Email { get; set; } = default!;
     public DateTime DateOfBirth { get; set; }
-    public List<string> EnrolledCourses { get; set; } = new();
+    public DateTime CreatedAtUtc { get; set; }
+    public List<string> EnrolledCourses { get; set; } = [];
 
     public void Apply(Event @event)
     {
@@ -17,28 +18,28 @@ public void Apply(Event @event)
             case StudentCreated created:
                 Apply(created);
                 break;
-            case StudentUpdated updated:
-                Apply(updated);
+            case StudentEmailChanged emailChanged:
+                Apply(emailChanged);
                 break;
             case StudentEnrolled enrolled:
                 Apply(enrolled);
                 break;
-            case StudentUnEnrolled unEnrolled:
-                Apply(unEnrolled);
+            case StudentWithdrawn withdrawn:
+                Apply(withdrawn);
                 break;
         }
     }
 
     private void Apply(StudentCreated @event)
     {
-        Id = @event.StudentId;
+        Id = @event.Id;
         FullName = @event.FullName;
         Email = @event.Email;
+        CreatedAtUtc = @event.CreatedAtUtc;
     }
 
-    private void Apply(StudentUpdated @event)
+    private void Apply(StudentEmailChanged @event)
     {
-        FullName = @event.FullName;
         Email = @event.Email;
     }
 
@@ -48,7 +49,7 @@ private void Apply(StudentEnrolled @event)
             EnrolledCourses.Add(@event.CourseName);
     }
 
-    private void Apply(StudentUnEnrolled @event)
+    private void Apply(StudentWithdrawn @event)
     {
         if (EnrolledCourses.Contains(@event.CourseName))
             EnrolledCourses.Add(@event.CourseName);