ASP.NET/01_IntroductionSessions/Session02/Notes/02_Notes.md

0. Middleware and Request Pipeline

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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.

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.

[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.

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.

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.

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.

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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.

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.

[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.

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.

public IActionResult EditProduct(int id, string name) {     
// Parameters are bound from the URL }

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