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content/01-Introductory-Sessions/Session02/Session02 Notes.md

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+# 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](https://learn.microsoft.com/en-us/aspnet/core/fundamentals/middleware/)
+
+### ✅ Routing in ASP.NET Core
+
+> Learn how incoming requests map to controller actions through routing.  
+> 🔗 [ASP.NET Core Routing Docs](https://learn.microsoft.com/en-us/aspnet/core/fundamentals/routing)
+
+### ✅ Controllers
+
+> Understand how to structure controllers and handle requests with actions.  
+> 🔗 [ASP.NET Core Controllers](https://learn.microsoft.com/en-us/aspnet/core/mvc/controllers/actions)
+
+## 📌 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`.
+
+````csharp
+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:
+
+```csharp
+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:
+
+```csharp
+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:
+
+```csharp
+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
+
+```csharp
+public class HomeController : Controller
+{
+    public IActionResult Index()
+    {
+        return View();
+    }
+}
+```
+
+---
+
+### ✅ Handling HTTP Methods
+
+Use attributes to define the HTTP method an action should handle:
+
+```csharp
+[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:
+
+```csharp
+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:
+
+```csharp
+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:
+
+- [Microsoft Docs](https://learn.microsoft.com/en-us/aspnet/core/)
+- ChatGPT 2025 sessions