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Add Mediator Implementation
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‎Mediator/EmailMessage.cs

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public record EmailMessage(string Subject);

‎Mediator/Handlers.cs

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public class EmailSender : INotificationHandler<EmailMessage>
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{
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public void Handle(EmailMessage notification)
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{
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Console.WriteLine($"Inside {nameof(EmailSender)}.Handle()...");
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Console.WriteLine($"Sending email with subject {notification.Subject}...");
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}
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}
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public class EmailArchiver : INotificationHandler<EmailMessage>
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{
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public void Handle(EmailMessage notification)
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{
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Console.WriteLine($"Inside {nameof(EmailArchiver)}.Handle()...");
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Console.WriteLine($"Archiving email with subject {notification.Subject}...");
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}
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}

‎Mediator/IMediator.cs

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public interface IMediator
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{
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void Send<TMessage>(TMessage message);
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}

‎Mediator/INotificationHandler.cs

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public interface INotificationHandler<T>
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{
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void Handle(T notification);
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}

‎Mediator/Mediator.cs

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public class Mediator : IMediator
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{
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private readonly NotificationHandlerRegistry handlerRegistry;
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public Mediator(NotificationHandlerRegistry handlerRegistry)
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{
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this.handlerRegistry = handlerRegistry;
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}
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public void Send<TMessage>(TMessage message)
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{
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if (!handlerRegistry.HasHandler<TMessage>())
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{
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throw new InvalidOperationException($"No handler registered for message type {typeof(TMessage).Name}");
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}
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var handlers = handlerRegistry.GetHandlers<TMessage>();
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foreach (var handler in handlers)
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{
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handler.Handle(message);
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}
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}
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}

‎Mediator/Mediator.csproj

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net7.0</TargetFramework>
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<ImplicitUsings>enable</ImplicitUsings>
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<Nullable>enable</Nullable>
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</PropertyGroup>
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<ItemGroup>
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<PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="7.0.0" />
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</ItemGroup>
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</Project>

‎Mediator/Mediator.sln

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Microsoft Visual Studio Solution File, Format Version 12.00
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Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Mediator", "Mediator.csproj", "{03CCC487-C218-4D95-A874-0CA42AE2494D}"
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EndProject
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Global
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GlobalSection(SolutionConfigurationPlatforms) = preSolution
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Debug|Any CPU = Debug|Any CPU
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Release|Any CPU = Release|Any CPU
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EndGlobalSection
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GlobalSection(ProjectConfigurationPlatforms) = postSolution
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{03CCC487-C218-4D95-A874-0CA42AE2494D}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
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{03CCC487-C218-4D95-A874-0CA42AE2494D}.Debug|Any CPU.Build.0 = Debug|Any CPU
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{03CCC487-C218-4D95-A874-0CA42AE2494D}.Release|Any CPU.ActiveCfg = Release|Any CPU
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{03CCC487-C218-4D95-A874-0CA42AE2494D}.Release|Any CPU.Build.0 = Release|Any CPU
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EndGlobalSection
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EndGlobal

‎Mediator/MediatorExtensions.cs

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using System.Reflection;
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using Microsoft.Extensions.DependencyInjection;
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public static class MediatorExtensions
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{
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public static IServiceCollection AddMediator(this IServiceCollection services, params Assembly[] assemblies)
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{
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// We allow multiple assemblies to scan - if the user doesn't add anything, we assume the current one
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// where we are looking for INotificationHandler<T>
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if (assemblies.Length == 0)
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{
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assemblies = new[] { Assembly.GetExecutingAssembly() };
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}
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services.AddSingleton<IMediator, Mediator>();
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// Register all handler types found in the specified assemblies.
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foreach (var assembly in assemblies)
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{
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var handlerTypes = assembly.ExportedTypes
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.Where(x => x.GetInterfaces().Any(y => y.IsGenericType && y.GetGenericTypeDefinition() == typeof(INotificationHandler<>)))
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.ToList();
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foreach (var handlerType in handlerTypes)
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{
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services.AddTransient(handlerType);
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}
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}
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// Build the handler registry using the registered handlers.
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services.AddSingleton<NotificationHandlerRegistry>(provider =>
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{
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var registry = new NotificationHandlerRegistry();
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foreach (var service in services)
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{
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if (service.ServiceType.GetInterfaces().Any(y => y.IsGenericType && y.GetGenericTypeDefinition() == typeof(INotificationHandler<>)))
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{
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// Get the INotificationHandler<T> instances from the container
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var handler = provider.GetServices(service.ServiceType);
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foreach (var h in handler.Where(s => s is not null))
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{
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var handlerInterface = h!.GetType().GetInterfaces().First();
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var messageType = handlerInterface.GetGenericArguments().First();
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typeof(NotificationHandlerRegistry)
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.GetMethod("AddHandler")!
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.MakeGenericMethod(messageType)
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.Invoke(registry, new[] { h });
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}
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}
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}
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return registry;
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});
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return services;
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}
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}

‎Mediator/NotificationHandlerRegistry.cs

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public class NotificationHandlerRegistry
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{
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// The handler has to hold objects as key, as we don't know the type of the message yet
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private readonly Dictionary<Type, object> handlers = new();
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public void AddHandler<T>(INotificationHandler<T> handler)
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{
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var messageType = typeof(T);
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if (!handlers.ContainsKey(messageType))
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{
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handlers[messageType] = new List<INotificationHandler<T>>();
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}
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((List<INotificationHandler<T>>)handlers[messageType]).Add(handler);
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}
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public bool HasHandler<T>() => handlers.ContainsKey(typeof(T));
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public IReadOnlyCollection<INotificationHandler<T>> GetHandlers<T>()
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=> handlers.TryGetValue(typeof(T), out var list) ? (List<INotificationHandler<T>>)list : Array.Empty<INotificationHandler<T>>();
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}

‎Mediator/ProducerService.cs

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public class ProducerService
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{
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private readonly IMediator _mediator;
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public ProducerService(IMediator mediator)
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{
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_mediator = mediator;
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}
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public void ProduceEmail(string subject)
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{
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_mediator.Send(new EmailMessage(subject));
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}
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}

‎Mediator/Program.cs

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using Microsoft.Extensions.DependencyInjection;
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var services = new ServiceCollection()
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.AddMediator()
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.AddScoped<ProducerService>()
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.BuildServiceProvider();
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var producer = services.GetRequiredService<ProducerService>();
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producer.ProduceEmail("Hello World");

‎Mediator/README.md

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# Create your own Mediator (like Mediatr)
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In this blog post, I'll show you the fundamentals of the Mediator pattern and how to implement it in your application from scratch. And yes, we basically implement the famous MediatR library.
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Found [here](https://steven-giesel.com/blogPost/dc27bbf9-55c7-4f11-bec5-cf1704df3a21)

‎README.md

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| BlogPost | Publish Date |
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| -------------------------------------------------------------------------------------------------------------- | ------------ |
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| [Create your own Mediator (like Mediatr)](Mediator/) | 21.06.2023 |
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| [Verifying your DI Container](ServiceCollectionVerify/) | 30.04.2023 |
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| [.NET 8 Performance Edition](BenchmarkDotNet8/) | 12.04.2023 |
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| [Creating a ToolTip Component in Blazor](BlazorToolTip/) | 31.03.2023 |

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