ASP.NET

Session02 Notes

3 min read

Session 2: Middleware, Routing, and Controllers in ASP.NET Core MVC

📝 Overview

In this session, we’ll cover the following concepts:

  • Middleware and the ASP.NET Core request pipeline
  • Routing structure: default, attribute-based, constraints, SEO-friendly
  • Creating and structuring controllers
  • Handling HTTP methods
  • Dependency Injection in controllers
  • Model binding and action parameters

📚 Topics Covered

✅ Middleware and Request Pipeline

Visual understanding of the middleware flow and pipeline order
🖼️ See diagrams in original session notes

🔗 ASP.NET Core Middleware Overview

✅ Routing in ASP.NET Core

Learn how incoming requests map to controller actions through routing.
🔗 ASP.NET Core Routing Docs

✅ Controllers

Understand how to structure controllers and handle requests with actions.
🔗 ASP.NET Core Controllers

📌 Notes

Collected from various sources including Microsoft Docs and ChatGPT

📍 Part 0: Middleware and Request Pipeline

🖼️ Diagrams:

  • [](../../../Assets/Pasted image 20241105101014.png)
  • [](../../../Assets/Pasted image 20241105111037.png)
  • [](../../../Assets/Pasted image 20241105111022.png)

📍 Part 1: Routing in ASP.NET Core MVC

Routing maps incoming HTTP requests to controller actions.

✅ Basic Routing Structure

Routing is configured in Program.cs via app.MapControllerRoute.

app.MapControllerRoute(
    name: "default",
    pattern: "{controller=Home}/{action=Index}/{id?}"
);
 
- `{controller=Home}`: default controller
 
- `{action=Index}`: default action
 
- `{id?}`: optional URL parameter
 
 
---
 
### ✅ Attribute Routing
 
Define routes directly in the controller using attributes:
 
```csharp
[Route("products")]
public class ProductsController : Controller
{
    [HttpGet("all")]
    public IActionResult GetAllProducts() { /*...*/ }
 
    [HttpGet("{id}")]
    public IActionResult GetProductById(int id) { /*...*/ }
}

✅ Route Parameters & Constraints

You can enforce patterns and types using constraints:

app.MapControllerRoute(
    name: "custom",
    pattern: "{controller=Products}/{action=List}/{id:int:min(1)}"
);
  • int:min(1) means id must be an integer ≥ 1
  • Other constraints: bool, datetime, guid, minlength(x), etc.

✅ Per-Controller Default Routes

You can assign a default action to a specific controller:

app.MapControllerRoute(
    name: "gallery",
    pattern: "Gallery/{action=Main}/{id?}",
    defaults: new { controller = "Gallery" }
);
 
app.MapControllerRoute(
    name: "default",
    pattern: "{controller=Home}/{action=Index}/{id?}"
);

✅ SEO-Friendly URLs

Use descriptive URLs for readability and SEO:

app.MapControllerRoute(
    name: "productDetail",
    pattern: "products/details/{id:int}/{name}"
);

✅ Example output: /products/details/10/laptop

📍 Part 2: Controllers in ASP.NET Core MVC

Controllers handle requests and return responses, acting as a bridge between models and views.

✅ Creating a Basic Controller

public class HomeController : Controller
{
    public IActionResult Index()
    {
        return View();
    }
}

✅ Handling HTTP Methods

Use attributes to define the HTTP method an action should handle:

[HttpPost]
public IActionResult CreateProduct(Product product)
{
    return RedirectToAction("Index");
}

Other attributes include:

  • [HttpGet]
  • [HttpPut]
  • [HttpDelete]

✅ Dependency Injection in Controllers

Inject services like repositories into controllers for better separation of concerns:

public class ProductsController : Controller
{
    private readonly IProductRepository _repository;
 
    public ProductsController(IProductRepository repository)
    {
        _repository = repository;
    }
}

✅ Action Parameters and Model Binding

Parameters are bound automatically from the URL, query string, or form body:

public IActionResult EditProduct(int id, string name)
{
    // id and name are bound from query or route
}

For complex types, ASP.NET Core binds data from the request body (e.g., forms or JSON).

🧪 Practice

  • Define multiple routes with custom constraints
  • Build an SEO-friendly route pattern
  • Create controller with basic actions (Index, Details, Create)
  • Add attribute-based routes to actions
  • Use [HttpGet], [HttpPost] on appropriate methods
  • Inject a service into a controller via constructor
  • Bind parameters from query and route

🙏 Acknowledgments

Sources:

Graph View

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