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01_IntroductionSessions/Session02/Notes/02_Notes.md

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+
+## **0. Middleware and Request Pipeline**
+![[Pasted image 20241105101014.png]]
+![[Pasted image 20241105111037.png]]
+
+![[Pasted image 20241105111022.png]]
+
+## **1. Routing in ASP.NET Core MVC**
+
+Routing is a mechanism to map incoming HTTP requests to specific controller actions. Understanding routing is crucial for managing URL patterns and making your app user-friendly and SEO-optimized.
+
+### **Basic Routing Structure**
+
+Routes in ASP.NET Core are configured in `Program.cs` (or `Startup.cs` in earlier versions) using the `app.MapControllerRoute` method, which defines how URLs map to controllers and actions.
+
+### **Steps and Key Concepts in Routing**
+
+1. **Define a Default Route** The default route defines the basic URL pattern that ASP.NET Core will follow.
+    
+```c#
+app.MapControllerRoute(name: "default", pattern: "{controller=Home}/{action=Index}/{id?}");
+```
+- **Pattern**: 
+	- `{controller=Home}/{action=Index}/{id?}`:
+	- `{controller=Home}`: Specifies the controller, defaulting to `Home`.
+	- `{action=Index}`: Specifies the action method, defaulting to `Index`.
+	- `{id?}`: Optional parameter for passing an `id`.
+1. **Attribute Routing** Define routes directly within the controller using attributes. This is useful when each action needs a unique route.
+    
+ ```c#
+[Route("products")] 
+public class ProductsController : Controller 
+{     
+	[HttpGet("all")]
+	public IActionResult GetAllProducts() { /*...*/ }      
+
+	[HttpGet("{id}")]     
+	public IActionResult GetProductById(int id) { /*...*/ } 
+}
+```
+1. **Custom Route Parameters and Constraints** You can add custom parameters and enforce constraints directly in the route to manage data types and URL patterns.
+        
+```c#
+app.MapControllerRoute(name: "custom", pattern: "{controller=Products}/{action=List}/{id:int:min(1)}");
+```
+
+- **Constraints**: `{id:int:min(1)}` ensures `id` is an integer greater than or equal to 1.
+- Other constraints include `bool`, `datetime`, `guid`, `minlength(x)`, `maxlength(x)`, and custom regular expressions.
+
+1. **Setting Default Actions Based on Controller** To give specific controllers a unique default action, create additional routes before the default route.
+    
+```c#
+app.MapControllerRoute(name: "gallery", pattern: "Gallery/{action=Main}/{id?}",defaults: new { controller = "Gallery" });  
+
+app.MapControllerRoute(name: "default", pattern: "{controller=Home}/{action=Index}/{id?}");
+```
+    
+1. **SEO-Friendly and Readable URLs** For user-friendly URLs, use meaningful route names instead of parameters. This is particularly useful for e-commerce or content-heavy sites.    
+```c#
+app.MapControllerRoute(name: "productDetail", pattern: "products/details/{id:int}/{name}");
+```
+
+This structure allows URLs like `/products/details/10/laptop`, which is clear and keyword-rich.
+
+---
+
+## **2. Controllers in ASP.NET Core MVC**
+
+Controllers are central in ASP.NET Core MVC and handle requests, retrieve data, and determine how it’s returned to the client.
+
+### **Controller Basics**
+
+- **Controller Naming**: Controllers usually end with "Controller" (e.g., `HomeController`, `ProductController`).
+- **Actions**: Methods within controllers are called action methods, typically returning a response to the user.
+
+### **Steps and Key Concepts in Controllers**
+
+1. **Creating a Basic Controller** A controller inherits from the `Controller` base class and contains action methods.
+    
+```c#
+public class HomeController : Controller 
+{     
+	public IActionResult Index()     
+	{         
+		return View();     
+	} 
+}
+```
+
+1. **Handling HTTP Methods with Attributes** Controllers use HTTP attributes like `[HttpGet]`, `[HttpPost]`, `[HttpPut]`, and `[HttpDelete]` to specify which HTTP methods they handle.
+    
+```c# 
+[HttpPost] 
+public IActionResult CreateProduct(Product product) 
+{     
+    //Handle POST request     
+	return RedirectToAction("Index"); 
+}
+```
+    
+3. **Using Dependency Injection in Controllers** Dependency injection is commonly used in ASP.NET Core to inject services (like a repository) into controllers, supporting clean code and testability.
+    
+```c#
+public class ProductsController : Controller 
+{     
+	private readonly IProductRepository _repository;
+    public ProductsController(IProductRepository repository)     
+    {         
+	    _repository = repository;     
+	    } 
+	}
+}
+```
+
+1. **Defining Action Parameters** Parameters passed to action methods are automatically bound from the URL or query string. Use model binding to parse complex objects from the request body.
+    
+    
+```c#
+public IActionResult EditProduct(int id, string name) {     
+// Parameters are bound from the URL }
+```
+
+
+---
+