ASP.NET Core Overview

ASP.NET Core is a modern, cross-platform framework for building high-performance, cloud-based, and internet-connected applications. It is designed to work on Windows, macOS, and Linux, making it versatile and flexible for various development scenarios.

Key Differences Between ASP.NET Core and ASP.NET

  1. Cross-Platform: ASP.NET Core is cross-platform, while ASP.NET (classic) is Windows-only.
  2. Performance: ASP.NET Core offers improved performance and scalability.
  3. Modular Design: ASP.NET Core is modular and allows you to include only the necessary components.
  4. Unified Programming Model: ASP.NET Core merges MVC and Web API into a single framework.
  5. Dependency Injection: ASP.NET Core has built-in support for dependency injection, unlike ASP.NET.
  6. Configuration: ASP.NET Core uses a new configuration system that is more flexible and extensible.

Role of the Startup Class

The Startup class is central to configuring an ASP.NET Core application. It includes methods to configure services (ConfigureServices) and the request processing pipeline (Configure). This class is where you set up middleware, configure dependency injection, and define application services.

Dependency Injection

Dependency Injection (DI) is a design pattern used to achieve Inversion of Control (IoC) between classes and their dependencies. ASP.NET Core has built-in support for DI, allowing you to manage dependencies in a clean, testable manner. It helps decouple components, making code easier to maintain and test.

Benefits of ASP.NET Core

  1. Cross-Platform: Works on Windows, macOS, and Linux.
  2. High Performance: Optimized for modern hardware and software architectures.
  3. Modular and Lightweight: Allows for more efficient applications by including only necessary components.
  4. Unified Framework: Combines MVC and Web API into a single framework.
  5. Built-In Dependency Injection: Facilitates a more maintainable and testable codebase.
  6. Flexible Configuration: Supports various configuration sources and options.

Request Processing Pipeline in ASP.NET Core

The request processing pipeline is composed of a series of middleware components that handle HTTP requests and responses. Each middleware component can perform operations on the request before passing it to the next middleware, and on the response before sending it to the client. Middleware components are configured in the Configure method of the Startup class.

Differentiating app.Run and app.Use

  • app.Use: Adds a middleware to the pipeline that can perform actions and pass control to the next middleware.
  • app.Run: Adds a terminal middleware that does not pass control to the next component in the pipeline.

Request Delegate

A request delegate is a function that handles HTTP requests. It takes an HttpContext as a parameter and returns a Task. It is used to process requests and responses within middleware components.

Host in ASP.NET Core

The Host is responsible for managing the app’s lifetime, including starting and stopping the application. It sets up the environment and dependency injection. There are two main types of hosts: Generic Host (for background services and console apps) and Web Host (for web applications).

Configuration in ASP.NET Core

Configuration in ASP.NET Core is managed through a flexible system that reads from various sources like appsettings.json, environment variables, command-line arguments, and more. Values from appsettings.json can be accessed using the IConfiguration interface.

Handling Static Files

ASP.NET Core serves static files (e.g., HTML, CSS, JavaScript) using the StaticFileMiddleware. This middleware is added to the pipeline using app.UseStaticFiles().

Session and State Management

  • Session: Used to store user-specific data across requests. Configured using services.AddSession() and app.UseSession().
  • State Management: Includes techniques like cookies, sessions, and query strings to persist user data.

Running ASP.NET Core in Docker

Yes, ASP.NET Core applications can run in Docker containers. Docker provides a consistent runtime environment, making it easier to deploy and manage applications across different environments.

Model Binding

Model binding in ASP.NET Core converts HTTP request data into .NET objects. It maps data from forms, query strings, and route data to action method parameters.

Model Validation

Model validation ensures that the data passed to a model is correct. Custom validation can be added by creating custom attributes inheriting from ValidationAttribute and applying them to model properties.

ASP.NET Core MVC Architecture

ASP.NET Core MVC uses the Model-View-Controller (MVC) pattern:

  • Model: Represents the data and business logic.
  • View: Renders the UI based on the model data.
  • Controller: Handles user input, manipulates the model, and returns the view.

Components of ASP.NET Core MVC

  • Model: Defines the data structure and business logic.
  • View: Defines the presentation layer.
  • Controller: Handles user requests and responses.

View Models

View models are used to pass data between the controller and view. They encapsulate data needed for rendering a view and may include multiple models or additional properties.

Routing in ASP.NET Core MVC

Routing maps incoming requests to the appropriate controller and action methods based on URL patterns. Routes can be defined in Startup.Configure using app.UseRouting() and app.UseEndpoints().

Attribute-Based Routing

Attribute-based routing allows defining routes directly on controller actions using attributes like [Route] or [HttpGet]. It provides more control over route templates and parameters.

Dependency Injection Problems Solved

  1. Tight Coupling: Reduces dependencies between components.
  2. Testability: Makes it easier to inject mock dependencies for unit testing.
  3. Flexibility: Facilitates configuration changes without modifying code.

Service Lifetimes

  1. Transient: Created each time they are requested.
  2. Scoped: Created once per request.
  3. Singleton: Created once and shared throughout the application.

Middleware Concept

Middleware are components in the request pipeline that handle HTTP requests and responses. They can perform tasks such as logging, authentication, and error handling.

Middleware Role

Middleware components are used to:

  • Process requests before they reach the application.
  • Modify responses before they are sent to the client.
  • Implement cross-cutting concerns like authentication and logging.

Options Pattern

The Options Pattern is used to configure and manage application settings. It involves creating classes to represent settings, binding them to configuration sections, and injecting them into services.

Managing Multiple Environments

ASP.NET Core supports multiple environments (Development, Staging, Production). You can configure environment-specific settings in appsettings.{Environment}.json and use the IWebHostEnvironment interface to check the current environment.

Logging System

ASP.NET Core provides a built-in logging system that supports various logging providers (Console, Debug, File). Logs can be configured in Startup.Configure and written using ILogger instances.

Routing in ASP.NET Core

Routing determines how HTTP requests are matched to endpoints (e.g., controllers, pages). It supports attribute-based routing and conventional routing, allowing flexible URL mappings.

Error and Exception Handling

Error handling in ASP.NET Core can be managed using exception handling middleware (app.UseExceptionHandler()), custom error pages, and logging.

Custom Model Binding

Custom model binding allows you to create your own logic for converting HTTP request data into model objects. Implement the IModelBinder interface and register it in Startup.ConfigureServices.

Custom Middleware

Custom middleware can be created by defining a class with a Invoke or InvokeAsync method. It is added to the pipeline using app.UseMiddleware<YourMiddleware>().

Accessing HttpContext

HttpContext provides information about the current request and response. It can be accessed through dependency injection in controllers and services.

Change Token

Change tokens are used to detect changes in configuration or settings. They allow applications to respond to changes dynamically without restarting.

ASP.NET Core APIs in Class Library

APIs in ASP.NET Core can be used in class libraries by referencing the necessary packages and using the HttpClient to make API requests.

Open Web Interface for .NET (OWIN)

OWIN is a specification for decoupling web applications from web servers. ASP.NET Core has its own hosting model but is designed to be compatible with OWIN middleware.

URL Rewriting Middleware

URL Rewriting Middleware allows modifying incoming request URLs based on rules. It can be used for redirecting or rewriting URLs for SEO or routing purposes.

Application Model

The application model represents the structure and behavior of the application. It includes components like controllers, views, and routes, defining how the application processes requests.

Caching Strategies

  • In-Memory Caching: Stores data in the memory of the server. Used for quick access.
  • Distributed Caching: Stores data in a distributed cache system (e.g., Redis) to share cache across multiple servers.

XSRF/CSRF Prevention

Cross-Site Request Forgery (CSRF) attacks can be prevented using anti-forgery tokens. ASP.NET Core includes built-in support for anti-forgery tokens using [ValidateAntiForgeryToken].

Cross-Site Scripting (XSS) Prevention

To prevent XSS attacks, ensure proper encoding of user input, validate and sanitize data, and use built-in HTML encoding features in ASP.NET Core.

Enabling CORS

Cross-Origin Resource Sharing (CORS) allows APIs to be accessed from different domains. It is enabled using the AddCors method in Startup.ConfigureServices and configured in Startup.Configure.

Dependency Injection for Controllers

In ASP.NET Core MVC, dependency

injection is used to provide services to controllers via constructor injection. Services are registered in Startup.ConfigureServices.

Dependency Injection for Views

For views, you typically use the IViewComponent interface or view-specific services. Dependency injection in views is less common but can be achieved using view components or custom tag helpers.

Unit Testing Controllers

Controllers can be unit tested by mocking dependencies and verifying the behavior of action methods. Use testing frameworks like xUnit or NUnit and mocking libraries like Moq.

Cache Tag Helper

The Cache Tag Helper helps cache parts of a view to improve performance. It allows caching output of a Razor page or view to reduce server load and improve response times.

Validation in ASP.NET Core MVC

Validation in ASP.NET Core MVC is achieved using data annotations and the validation attributes applied to model properties. It supports client-side and server-side validation, following the DRY principle.

Strongly Typed Views

Strongly typed views are views that are bound to a specific model type, providing IntelliSense and compile-time checking. They improve type safety and development efficiency.

Partial Views

Partial views are reusable components that can be rendered within other views. They are useful for sharing common UI elements across multiple views.

Security Concerns in ASP.NET Core

ASP.NET Core handles security through features like authentication, authorization, and secure communication. Best practices include using HTTPS, implementing role-based and policy-based authorization, and securing sensitive data.