🧩 Implementing a Lightweight Query Handler in .NET using GMediator fully free for commerical use

In modern .NET applications, maintaining clean architecture is critical — and that’s where the Mediator pattern shines. It decouples the request/response flow and promotes separation of concerns.

While libraries like MediatR are popular, sometimes you want something even lighter — with zero dependencies.

Enter: GMediator, a custom lightweight mediator implementation.

🚀 What We’ll Build
In this blog, we’ll create a simple GET API using GMediator that returns a list of products stored in an in-memory store — no database, no ORM — just the core pattern in action.
🧱 Step 1: Define the Product Model

Code Snippet

public class Product { public Guid Id { get; set; } = Guid.NewGuid(); public string Name { get; set; } public decimal Price { get; set; } }

💾 Step 2: Create an In-Memory Store

Code Snippet

public static class ProductStore { public static List<Product> Products { get; set; } = new() { new Product { Name = "Laptop", Price = 1200 }, new Product { Name = "Mouse", Price = 20 }, new Product { Name = "Keyboard", Price = 45 } }; }

📬 Step 3: Create the Query Request

Code Snippet

using GMediator.Interfaces; public class GetAllProducts : IRequest<List<Pro>> { } public class Pro { public Guid Id { get; set; } = Guid.NewGuid(); public string Name { get; set; } public decimal Price { get; set; } } 🧠 Step 4: Implement the Query Handler using GMediator.Interfaces; public class GetAllProductsHandler : IRequestHandler<GetAllProducts, List<Pro>> { public Task<List<Pro>> Handle(GetAllProducts request, CancellationToken cancellationToken) { var products = ProductStore.Products .Select(x => new Pro { Id = x.Id, Name = x.Name, Price = x.Price }) .ToList(); // Important: convert to List<Pro> return Task.FromResult(products); } }

🎯 Step 5: Create the Controller

Code Snippet

[ApiController] [Route("api/[controller]")] public class ProductsController : ControllerBase { private readonly IMediator _mediator; public ProductsController(IMediator mediator) { _mediator = mediator; } [HttpGet] public async Task<IActionResult> Get() { var products = await _mediator.Send(new GetAllProducts()); return Ok(products); } }

🧪 Step 6: Register GMediator in Program.cs

Code Snippet

builder.Services.AddGMediator(); // Register your custom GMediator

💡 Final Thoughts
GMediator is a great option for internal projects, low-dependency APIs, or learning the Mediator pattern hands-on.
You can extend this by adding Create, Update, Delete, or integrating with a real database like SQLite or SQL Server.