update introducery sessions notes
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Ali Taherzadeh
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# Session 2: Middleware, Routing, and Controllers in ASP.NET Core MVC
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## **0. Middleware and Request Pipeline**
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![[Pasted image 20241105101014.png]]
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![[Pasted image 20241105111037.png]]
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## 📝 Overview
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![[Pasted image 20241105111022.png]]
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In this session, we’ll cover the following concepts:
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## **1. Routing in ASP.NET Core MVC**
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- Middleware and the ASP.NET Core request pipeline
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- Routing structure: default, attribute-based, constraints, SEO-friendly
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- Creating and structuring controllers
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- Handling HTTP methods
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- Dependency Injection in controllers
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- Model binding and action parameters
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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.
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## 📚 Topics Covered
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### **Basic Routing Structure**
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### ✅ Middleware and Request Pipeline
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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.
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> Visual understanding of the middleware flow and pipeline order
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> 🖼️ _See diagrams in original session notes_
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### **Steps and Key Concepts in Routing**
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🔗 [ASP.NET Core Middleware Overview](https://learn.microsoft.com/en-us/aspnet/core/fundamentals/middleware/)
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1. **Define a Default Route** The default route defines the basic URL pattern that ASP.NET Core will follow.
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```c#
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app.MapControllerRoute(name: "default", pattern: "{controller=Home}/{action=Index}/{id?}");
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```
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- **Pattern**:
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- `{controller=Home}/{action=Index}/{id?}`:
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- `{controller=Home}`: Specifies the controller, defaulting to `Home`.
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- `{action=Index}`: Specifies the action method, defaulting to `Index`.
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- `{id?}`: Optional parameter for passing an `id`.
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1. **Attribute Routing** Define routes directly within the controller using attributes. This is useful when each action needs a unique route.
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```c#
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[Route("products")]
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public class ProductsController : Controller
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{
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[HttpGet("all")]
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public IActionResult GetAllProducts() { /*...*/ }
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### ✅ Routing in ASP.NET Core
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[HttpGet("{id}")]
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public IActionResult GetProductById(int id) { /*...*/ }
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}
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```
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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.
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```c#
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app.MapControllerRoute(name: "custom", pattern: "{controller=Products}/{action=List}/{id:int:min(1)}");
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```
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> Learn how incoming requests map to controller actions through routing.
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> 🔗 [ASP.NET Core Routing Docs](https://learn.microsoft.com/en-us/aspnet/core/fundamentals/routing)
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- **Constraints**: `{id:int:min(1)}` ensures `id` is an integer greater than or equal to 1.
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- Other constraints include `bool`, `datetime`, `guid`, `minlength(x)`, `maxlength(x)`, and custom regular expressions.
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### ✅ Controllers
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1. **Setting Default Actions Based on Controller** To give specific controllers a unique default action, create additional routes before the default route.
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```c#
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app.MapControllerRoute(name: "gallery", pattern: "Gallery/{action=Main}/{id?}",defaults: new { controller = "Gallery" });
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> Understand how to structure controllers and handle requests with actions.
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> 🔗 [ASP.NET Core Controllers](https://learn.microsoft.com/en-us/aspnet/core/mvc/controllers/actions)
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app.MapControllerRoute(name: "default", pattern: "{controller=Home}/{action=Index}/{id?}");
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```
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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.
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```c#
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app.MapControllerRoute(name: "productDetail", pattern: "products/details/{id:int}/{name}");
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```
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## 📌 Notes
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This structure allows URLs like `/products/details/10/laptop`, which is clear and keyword-rich.
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> _Collected from various sources including Microsoft Docs and ChatGPT_
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---
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## **2. Controllers in ASP.NET Core MVC**
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## 📍 Part 0: Middleware and Request Pipeline
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Controllers are central in ASP.NET Core MVC and handle requests, retrieve data, and determine how it’s returned to the client.
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🖼️ **Diagrams**:
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### **Controller Basics**
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- ![[Pasted image 20241105101014.png]]
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- ![[Pasted image 20241105111037.png]]
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- ![[Pasted image 20241105111022.png]]
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- **Controller Naming**: Controllers usually end with "Controller" (e.g., `HomeController`, `ProductController`).
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- **Actions**: Methods within controllers are called action methods, typically returning a response to the user.
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---
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### **Steps and Key Concepts in Controllers**
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## 📍 Part 1: Routing in ASP.NET Core MVC
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1. **Creating a Basic Controller** A controller inherits from the `Controller` base class and contains action methods.
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```c#
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public class HomeController : Controller
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{
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public IActionResult Index()
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{
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return View();
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}
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}
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```
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Routing maps incoming HTTP requests to controller actions.
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1. **Handling HTTP Methods with Attributes** Controllers use HTTP attributes like `[HttpGet]`, `[HttpPost]`, `[HttpPut]`, and `[HttpDelete]` to specify which HTTP methods they handle.
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```c#
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[HttpPost]
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public IActionResult CreateProduct(Product product)
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{
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//Handle POST request
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return RedirectToAction("Index");
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}
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```
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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.
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```c#
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public class ProductsController : Controller
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{
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private readonly IProductRepository _repository;
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public ProductsController(IProductRepository repository)
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{
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_repository = repository;
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}
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}
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}
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```
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### ✅ Basic Routing Structure
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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.
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```c#
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public IActionResult EditProduct(int id, string name) {
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// Parameters are bound from the URL }
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```
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Routing is configured in `Program.cs` via `app.MapControllerRoute`.
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````csharp
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app.MapControllerRoute(
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name: "default",
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pattern: "{controller=Home}/{action=Index}/{id?}"
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);
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- `{controller=Home}`: default controller
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- `{action=Index}`: default action
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- `{id?}`: optional URL parameter
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---
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### ✅ Attribute Routing
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Define routes directly in the controller using attributes:
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```csharp
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[Route("products")]
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public class ProductsController : Controller
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{
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[HttpGet("all")]
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public IActionResult GetAllProducts() { /*...*/ }
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[HttpGet("{id}")]
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public IActionResult GetProductById(int id) { /*...*/ }
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}
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````
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---
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### ✅ Route Parameters & Constraints
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You can enforce patterns and types using constraints:
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```csharp
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app.MapControllerRoute(
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name: "custom",
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pattern: "{controller=Products}/{action=List}/{id:int:min(1)}"
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);
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```
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- `int:min(1)` means `id` must be an integer ≥ 1
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- Other constraints: `bool`, `datetime`, `guid`, `minlength(x)`, etc.
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---
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### ✅ Per-Controller Default Routes
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You can assign a default action to a specific controller:
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```csharp
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app.MapControllerRoute(
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name: "gallery",
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pattern: "Gallery/{action=Main}/{id?}",
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defaults: new { controller = "Gallery" }
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);
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app.MapControllerRoute(
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name: "default",
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pattern: "{controller=Home}/{action=Index}/{id?}"
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);
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```
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---
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### ✅ SEO-Friendly URLs
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Use descriptive URLs for readability and SEO:
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```csharp
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app.MapControllerRoute(
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name: "productDetail",
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pattern: "products/details/{id:int}/{name}"
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);
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```
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✅ Example output: `/products/details/10/laptop`
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---
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## 📍 Part 2: Controllers in ASP.NET Core MVC
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Controllers handle requests and return responses, acting as a bridge between models and views.
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### ✅ Creating a Basic Controller
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```csharp
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public class HomeController : Controller
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{
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public IActionResult Index()
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{
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return View();
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}
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}
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```
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---
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### ✅ Handling HTTP Methods
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Use attributes to define the HTTP method an action should handle:
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```csharp
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[HttpPost]
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public IActionResult CreateProduct(Product product)
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{
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return RedirectToAction("Index");
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}
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```
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Other attributes include:
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- `[HttpGet]`
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- `[HttpPut]`
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- `[HttpDelete]`
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---
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### ✅ Dependency Injection in Controllers
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Inject services like repositories into controllers for better separation of concerns:
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```csharp
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public class ProductsController : Controller
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{
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private readonly IProductRepository _repository;
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public ProductsController(IProductRepository repository)
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{
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_repository = repository;
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}
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}
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```
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---
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### ✅ Action Parameters and Model Binding
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Parameters are bound automatically from the URL, query string, or form body:
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```csharp
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public IActionResult EditProduct(int id, string name)
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{
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// id and name are bound from query or route
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}
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```
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For complex types, ASP.NET Core binds data from the request body (e.g., forms or JSON).
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---
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## 🧪 Practice
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- Define multiple routes with custom constraints
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- Build an SEO-friendly route pattern
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- Create controller with basic actions (`Index`, `Details`, `Create`)
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- Add attribute-based routes to actions
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- Use `[HttpGet]`, `[HttpPost]` on appropriate methods
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- Inject a service into a controller via constructor
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- Bind parameters from query and route
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## 🙏 Acknowledgments
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Sources:
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- [Microsoft Docs](https://learn.microsoft.com/en-us/aspnet/core/)
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- ChatGPT 2025 sessions
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