ASP.NET Core Intermediate Interview Questions and Answers

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ASP.NET Core Intermediate Interview Questions and Answers

In this article, I will discuss the most frequently asked Top 50 ASP.NET Core Intermediate Interview Questions and Answers. Please read our previous article discussing Top 50 ASP.NET Core Basic Interview Questions and Answers. Here’s a comprehensive list of ASP.NET Core Intermediate Interview Questions and Answers.

Explain the design principles behind ASP.NET Core. How does it differ from previous versions of ASP.NET?

ASP.NET Core was designed with the principles of modularity, cross-platform functionality, and performance in mind. It represents a significant departure from previous versions of ASP.NET by:

• Modularity: ASP.NET Core allows developers to include only the components they need, reducing application size and improving performance.
• Cross-Platform: It can run on Windows, Linux, and macOS, making it more versatile than its predecessor.
• Performance: ASP.NET Core is optimized for modern web applications, offering improved performance due to its lightweight and modular nature.

What is Kestrel? How does it compare to other web servers like IIS or Apache?

Kestrel is a cross-platform web server for ASP.NET Core. It is built on the libuv library, which provides asynchronous I/O operations. Kestrel can be used as a standalone web server or behind a reverse proxy like IIS or Apache. Compared to IIS and Apache, Kestrel is designed to be fast and lightweight, optimized for running ASP.NET Core applications. While IIS and Apache offer more built-in features and management tools, Kestrel provides better performance in ASP.NET Core environments.

What is Razor Pages in ASP.NET Core? How does it differ from MVC?

Razor Pages is a page-based coding model that makes building web UI easier and more productive. Unlike MVC, which requires controllers and views, Razor Pages integrates the page model directly with view rendering, simplifying page-focused scenarios. It’s part of the MVC framework but focuses on page-centric architectures, making it straightforward for developers to work on individual pages.

Explain Tag Helpers in ASP.NET Core. Provide examples of when and how to use them.

Tag Helpers enable server-side code to participate in creating and rendering HTML elements in Razor files. They are used for linking CSS, generating form elements, or creating custom components. For instance, the AnchorTagHelper can be used to generate links, while the FormTagHelper is used for form submissions. Tag Helpers improve the readability of Razor markup and provide a more HTML-like development experience.

What is the purpose of the Startup.cs file in an ASP.NET Core application?

The Startup.cs file is where you configure the services and the request pipeline for an ASP.NET Core application. It contains two methods:

• ConfigureServices: Used to add services to the application’s DI container.
• Configure: Used to define how the app responds to HTTP requests, essentially setting up the request processing pipeline with middleware.

How do you configure logging in ASP.NET Core?

Logging in ASP.NET Core is configured in the Startup.cs file by calling AddLogging on the IServiceCollection in the ConfigureServices method and by setting up logging providers (e.g., Console, Debug, EventSource) in the appsettings.json file or programmatically in the Configure method. ASP.NET Core uses a logging API that supports multiple providers and categories, making it flexible and extensible.

What is the role of the appsettings.json file in ASP.NET Core? How do you access settings from this file in your application?

The appsettings.json file in ASP.NET Core is used for storing configuration settings like connection strings, logging configurations, and application-specific settings. Settings from this file can be accessed in the application through the IConfiguration interface, which is typically injected into classes where configurations are needed.

Explain the concept of Middleware in ASP.NET Core. Provide examples of commonly used middleware.

Middleware in ASP.NET Core is software that’s assembled into an application pipeline to handle requests and responses. Each component chooses whether to pass the request to the next component in the pipeline and can perform operations before and after the next component. Commonly used middleware includes:

• Static File Middleware for serving static files.
• Authentication Middleware for authentication.
• MVC Middleware for handling MVC requests.

What are the benefits of using dependency injection in ASP.NET Core? How do you implement it?

Dependency Injection (DI) in ASP.NET Core provides a way to inject object dependencies at runtime rather than at compile time. This promotes a loosely coupled design, improving testability and maintenance. ASP.NET Core includes a built-in DI container that supports constructor injection by default, making it easy to implement DI throughout your application.

What is the difference between services.AddTransient, services.AddScoped, and services.AddSingleton in ASP.NET Core dependency injection?

• services.AddTransient: Creates a new instance each time the service is requested.
• services.AddScoped: Creates a single instance within the scope per request. Ideal for data operations within a single request.
• services.AddSingleton: Creates a single instance that persists for the application’s lifetime and is shared across all requests. Useful for services that are stateless or need to maintain state globally.

Explain the differences between HttpContext, HttpRequest, and HttpResponse in ASP.NET Core.

• HttpContext: Represents the context of an individual HTTP request in ASP.NET Core. It includes all information about the current HTTP request, including HttpRequest, HttpResponse, and other request-specific features like authentication data, session data, and environment information.
• HttpRequest: Part of the HttpContext, it encapsulates all HTTP-specific information about an incoming request. This includes details like the query string, form data, headers, cookies, and the HTTP method used (GET, POST, etc.).
• HttpResponse: Also part of the HttpContext, it represents the outgoing response that the server will send back to the client. This includes everything that you want to send back to the client, such as response headers, cookies, and the body content.

How do you handle exceptions globally in ASP.NET Core?

To handle exceptions globally in ASP.NET Core, you can use the middleware UseExceptionHandler in the Configure method of the Startup class. This middleware can be configured to redirect to a specific error-handling route or page, which can log and return the appropriate response to the client.

app.UseExceptionHandler(“/error”);

Additionally, for more granular control, especially for APIs, you can implement a custom exception handling middleware or use UseStatusCodePages middleware, which provides a way to handle specific HTTP status codes.

What is the difference between authentication and authorization in ASP.NET Core?

Authentication is the process of verifying who a user is. It involves validating user credentials (like username and password) against a known store (such as a database) to confirm the user’s identity.

Authorization is the process of determining what resources and operations a user can access or perform after they are authenticated. It involves checking whether an authenticated user has the right permissions to access a resource or execute an action.

How do you implement authentication and authorization using JWT in ASP.NET Core?

To implement authentication and authorization using JWT (JSON Web Tokens) in ASP.NET Core, you first need to configure the JWT bearer token service in the Startup.cs file by adding the JWT bearer authentication scheme to the ConfigureServices method. Then, you issue JWT tokens from your login or authentication endpoint. Tokens typically include claims that are used for authorization decisions. You secure endpoints using the [Authorize] attribute, optionally specifying roles or policies that dictate access.

What are policy-based authorization and resource-based authorization in ASP.NET Core?

Policy-based authorization involves defining policies with specific requirements (like a minimum age, membership duration, or having certain roles or claims) and applying those policies to controllers or actions using the [Authorize(Policy = “PolicyName”)] attribute.

Resource-based authorization involves making authorization decisions based on the resource being accessed and the user’s operation on it. This is typically implemented programmatically within your code, where you check whether a user has permission to perform an action on a resource.

Explain the role of Claims-based authentication in ASP.NET Core.

Claims-based authentication uses claims to convey information about a user’s identity and permissions. A claim is a statement about a user, such as name, role, age, etc. In ASP.NET Core, claims-based authentication is a flexible way to authenticate users and authorize access, allowing applications to make decisions based on the rich set of claims attached to the authenticated user.

What is Entity Framework Core? How does it differ from Entity Framework 6?

Entity Framework Core (EF Core) is a lightweight, extensible, and cross-platform version of Entity Framework, a popular Object-Relational Mapping (ORM) framework for .NET. EF Core is designed to work with both .NET Core and .NET Framework. Compared to Entity Framework 6, EF Core offers improved performance, a modular design that allows for non-relational databases, and support for asynchronous programming patterns.

How do you configure Entity Framework Core in an ASP.NET Core application?

To configure Entity Framework Core in an ASP.NET Core application, you typically add the EF Core package for your database provider (e.g., SQL Server, PostgreSQL) to your project. In the Startup.cs file, you configure the database context using the ConfigureServices method using the AddDbContext extension method, specifying the connection string and other options as needed.

What are migrations in Entity Framework Core? How do you create and apply them?

Migrations in Entity Framework Core are a way to manage and apply schema changes to your database over time. You create a migration using the Add-Migration <MigrationName> command in the Package Manager Console or dotnet ef migrations add <MigrationName> using the .NET CLI. To apply migrations to your database, you use the Update-Database command in the Package Manager Console or dotnet ef database update using the .NET CLI.

Explain the Repository pattern. How do you implement it with Entity Framework Core in ASP.NET Core?

The Repository pattern abstracts the data layer, providing a collection-like interface for accessing domain objects. It helps decouple the application’s business logic from data access logic. To implement it with Entity Framework Core in an ASP.NET Core application, you define repository interfaces and classes that use an EF Core context to perform CRUD operations. These repositories are then injected into your services or controllers, allowing for cleaner, more maintainable code by separating concerns.

What are Data Transfer Objects (DTOs)? When and why would you use them in an ASP.NET Core application?

DTOs are simple objects that are used to transfer data between processes or layers in an application without unnecessary data or behavior. In ASP.NET Core applications, you use DTOs to send only the required data from the server to the client or vice versa, particularly when working with APIs. This approach helps improve performance by reducing payload size and ensuring that sensitive data is not exposed inadvertently. DTOs also help in decoupling the internal domain model from the external interface, making the system more robust to changes.

What is the difference between DbContext.SaveChanges and DbContext.SaveChangesAsync in Entity Framework Core?

DbContext.SaveChanges executes synchronously and blocks the calling thread until the operation is completed. It commits all changes made in the context of the database. On the other hand, DbContext.SaveChangesAsync performs the same operation asynchronously without blocking the calling thread, allowing for a more responsive application, especially in web environments where I/O operations can be time-consuming. SaveChangesAsync is particularly beneficial in ASP.NET Core applications for improving scalability and responsiveness.

Explain the concept of Inversion of Control (IoC) and how it is implemented in ASP.NET Core.

Inversion of Control (IoC) is a design principle where the control of objects or portions of a program is transferred to a container or framework. It’s primarily used for managing dependencies between objects. In ASP.NET Core, IoC is implemented through a built-in Dependency Injection (DI) container. This container is responsible for instantiating classes and managing their lifecycles, allowing for loosely coupled components, which increases the modularity and testability of the application.

What is the role of the appsettings.Development.json file in an ASP.NET Core application?

The appsettings.Development.json file is used to store configuration settings that are specific to the development environment in an ASP.NET Core application. This allows developers to have settings like connection strings, logging levels, and other environment-specific configurations that differ from production or other environments. This file overrides the settings in the appsettings.json file when running in the development environment, ensuring that sensitive production data is not exposed during development.

How do you handle cross-cutting concerns such as logging, caching, and validation in ASP.NET Core?

In ASP.NET Core, cross-cutting concerns like logging, caching, and validation are handled through the use of middleware, filters, and attributes. Middleware components are used to implement concerns globally across all requests (e.g., logging and caching). Filters and attributes can be applied to controllers or actions to handle concerns like validation and caching at a more granular level. Dependency Injection (DI) is also leveraged to inject services such as logging and caching into classes where they are needed.

Explain the concept of CORS (Cross-Origin Resource Sharing) in ASP.NET Core. How do you configure it?

CORS is a security feature that allows or restricts web applications from making requests to resources hosted on a domain different from the one the application was served from. In ASP.NET Core, CORS can be configured using middleware. You configure it by adding the CORS services in the ConfigureServices method of the Startup class and then enabling CORS with the desired policy in the Configure method. This setup allows specifying which origins, headers, and methods are allowed for cross-origin requests.

What are the benefits of using middleware for exception handling in ASP.NET Core compared to traditional try-catch blocks?

Using middleware for exception handling in ASP.NET Core allows for centralized error management, reducing code duplication and ensuring consistency in handling exceptions across the application. Unlike scattered try-catch blocks, middleware provides a clean and unobtrusive way to catch and respond to errors from a single location. It also allows for the separation of error-handling logic from business logic, making the code cleaner and easier to maintain.

What are Health Checks in ASP.NET Core? How do you implement them?

Health Checks in ASP.NET Core are used to monitor the status and health of an application and its dependencies, such as databases and external services. They are implemented by registering health check services in the ConfigureServices method of the Startup class and configuring a health check endpoint in the Configure method. Health checks can then be used by external monitoring services or load balancers to determine the health of an application, facilitating automatic failover or alerting mechanisms.

Explain the concept of versioning APIs in ASP.NET Core. How do you version your APIs?

API versioning in ASP.NET Core allows you to support multiple versions of an API simultaneously, ensuring backward compatibility while allowing for new features and changes. Versioning can be achieved through different methods, such as URL path, query string parameters, header values, or content negotiation. ASP.NET Core supports API versioning through the Microsoft.AspNetCore.Mvc.Versioning package, which provides attributes and services to define and manage API versions easily.

What is SignalR? How do you implement real-time communication using SignalR in ASP.NET Core?

SignalR is a library for ASP.NET Core that enables real-time web functionality, allowing server-side code to push content to clients instantly. It’s used for applications that require high-frequency updates from the server, such as chat applications, live gaming, real-time monitoring, and more. To implement SignalR, you add the SignalR service to the ConfigureServices method in Startup, define hubs that manage connections and communication, and configure routes for these hubs in the Configure method. Clients can then connect to these hubs using the SignalR JavaScript client or other client SDKs to send and receive real-time messages.

What are the advantages of using DI containers like Autofac or Unity over the built-in DI container in ASP.NET Core?

The built-in DI container in ASP.NET Core is designed to be lightweight and straightforward, catering to most development needs. However, third-party DI containers like Autofac or Unity offer advanced features such as:

• Property and Method Injection: Beyond constructor injection, allowing for more complex scenarios.
• Advanced Lifetime Management: More sophisticated control over object lifetimes and scopes.
• AOP Support: Facilitating aspects like logging, transaction management, etc., through dynamic proxies.
• Better Support for Generic Types: Enhanced capabilities for resolving generic types.
• Performance: In certain scenarios, third-party containers might offer performance optimizations tailored to specific needs.

These features make third-party DI containers attractive for complex applications requiring more than the basic functionalities provided by the built-in DI container.

How do you handle file uploads in ASP.NET Core?

File uploads in ASP.NET Core can be handled using the IFormFile interface in an action method. Here’s a simplified example:

[HttpPost]
public async Task<IActionResult> UploadFile(IFormFile file)
{
    if (file == null || file.Length == 0)
    {
        return BadRequest("No file uploaded.");
    }

    var path = Path.Combine(Directory.GetCurrentDirectory(), "uploads", file.FileName);

    using (var stream = new FileStream(path, FileMode.Create))
    {
        await file.CopyToAsync(stream);
    }

    return Ok("File successfully uploaded.");
}

This code snippet demonstrates receiving a file from a form submission, validating it, and saving it to a predefined location on the server.

Explain the concept of Action Filters in ASP.NET Core. Provide examples of when and how to use them.

Action Filters in ASP.NET Core allow you to execute code before or after specific stages in the action execution pipeline. They’re useful for concerns like logging, authentication, caching, or modifying the result of an action. For example, an action filter could log the execution time of action methods or apply custom authorization checks.

You can apply action filters globally, at the controller level, or the action level using attributes. Here’s an example of a simple logging filter:

public class LogActionFilter : IActionFilter
{
    public void OnActionExecuting(ActionExecutingContext context)
    {
        // Code before the action executes
        Log("Before executing action");
    }

    public void OnActionExecuted(ActionExecutedContext context)
    {
        // Code after the action executes
        Log("After executing action");
    }

    private void Log(string message)
    {
        // Logging logic here
    }
}

This filter logs messages before and after an action method executes.

What are the benefits of using the Factory pattern in ASP.NET Core? Provide examples.

The Factory pattern is beneficial in ASP.NET Core for creating instances of objects without specifying the exact class of the object that will be created. This is particularly useful for:

• Decoupling Code: Reducing dependencies between the application’s components, thereby making the system more modular and easier to maintain or extend.
• Supporting Advanced Scenarios: Like conditional instantiation of different classes based on runtime parameters or configuration.
• Enhancing Testability: By allowing mocking of objects for unit tests.

For example, a payment processing system might use a factory to instantiate different payment service objects based on the payment method selected by the user.

How do you handle distributed caching in ASP.NET Core?

ASP.NET Core supports distributed caching using implementations like Redis or SQL Server. This allows applications to maintain a consistent cache across multiple server instances in a web farm or cloud environment. You configure the distributed cache in the Startup.cs file:

services.AddStackExchangeRedisCache(options =>
{
    options.Configuration = "localhost";
    options.InstanceName = "SampleInstance";
});

You can then inject IDistributedCache into your services or controllers to interact with the cache.

Explain the role of IHostedService and BackgroundService in ASP.NET Core.

IHostedService and BackgroundService (which is an abstract class implementing IHostedService) allow you to run background tasks in a web application. These are useful for tasks that need to run outside the request processing pipeline, such as background data processing, scheduled tasks, or integrating long-running operations.

BackgroundService provides a base for implementing long-running IHostedService with a background task loop. Implementations should override the ExecuteAsync method to execute the background task.

What is gRPC? How do you implement gRPC services in ASP.NET Core?

gRPC is a high-performance, open-source universal RPC framework. In ASP.NET Core, you can implement gRPC services by:

• Defining your service in a .proto file.
• Generating the server and client code using the Grpc.Tools NuGet package.
• Implementing the service class derived from the generated base class.
• Configuring the gRPC services in the Startup.cs file.
• gRPC services in ASP.NET Core support both unary and streaming calls and can be consumed by clients built in any language that supports gRPC.

What are the benefits of using Swagger/OpenAPI for documenting ASP.NET Core APIs?

Swagger (OpenAPI) provides a standardized, language-agnostic interface to REST APIs, allowing both humans and computers to discover and understand the capabilities of the service without access to source code, documentation, or network traffic. Benefits include:

• Interactive Documentation: Allows consumers to easily test and interact with the API.
• Client SDK Generation: Enables automatic generation of client libraries in various programming languages.
• API Discoverability and Testing: Simplifies the process of discovering and understanding API endpoints and their expected parameters and responses.

Integration with ASP.NET Core can be easily achieved using the Swashbuckle.AspNetCore package.

Explain the concept of Application Insights. How do you integrate it into an ASP.NET Core application?

Application Insights is an extensible Application Performance Management (APM) service for web developers, supporting multiple platforms. It helps you monitor your live applications by automatically detecting performance anomalies, providing powerful analytics, and enabling diagnostic logging.

To integrate Application Insights into an ASP.NET Core application, you can:

• Add the Application Insights SDK via the NuGet package.
• Configure the service in the Startup.cs or through the appsettings.json file with the Instrumentation Key.
• Use the Application Insights API to track custom events, metrics, or dependencies.

What is the purpose of the IWebHostEnvironment interface in ASP.NET Core?

The IWebHostEnvironment interface provides information about the web hosting environment in which an application is running. It allows applications to programmatically adjust their behavior based on the environment name (e.g., Development, Staging, Production) by enabling/disabling certain features or choosing different configuration files. It is typically injected into the Startup class, where environment-specific configurations can be applied.

How do you handle routing in ASP.NET Core?

Routing in ASP.NET Core is handled through a middleware that matches HTTP requests to endpoint handlers. Routes can be configured in the Startup.cs file using the app.UseEndpoints method, where you can define patterns for URLs and map them to controllers and actions (for MVC apps) or Razor Pages. ASP.NET Core supports both conventional routing, where routes are defined explicitly, and attribute routing, where routes are defined via attributes on controllers or actions.

What is the purpose of the IApplicationBuilder interface in ASP.NET Core?

IApplicationBuilder is used in the Configure method of the Startup.cs file to configure the HTTP request pipeline of an ASP.NET Core application. It provides a mechanism to register middleware components in a specific order. Each middleware can perform operations before and after the next component in the pipeline, allowing for tasks such as authentication, routing, and response generation.

Explain the differences between IIS Hosting, Kestrel Hosting, and Self Hosting in ASP.NET Core.

• IIS Hosting: Uses IIS as a reverse proxy with Kestrel or HTTP.sys as the underlying web server. IIS manages process activation and provides an additional layer of security and manageability.
• Kestrel Hosting: A cross-platform web server for ASP.NET Core, used for hosting directly on a network edge, capable of running without a reverse proxy in front of it, recommended to be used with a reverse proxy for production.
• Self Hosting: Refers to hosting the application within a custom process (like a Windows service or console application) using Kestrel or HTTP.sys directly, providing full control over the hosting environment.

What are the benefits of using the HttpClientFactory in ASP.NET Core to make HTTP requests?

HttpClientFactory offers several benefits for managing HttpClient instances in ASP.NET Core applications:

• Lifecycle Management: It handles the pooling and lifecycle of HttpClient instances, avoiding socket exhaustion issues.
• Policies: It integrates with Polly, allowing easy implementation of retry policies, circuit breakers, and more.
• Configuration: It allows for centralized configuration of HttpClient instances, making it easier to apply consistent settings across the application.

Explain the concept of scaffolding in ASP.NET Core. How do you use it to generate code?

Scaffolding in ASP.NET Core is a code generation framework that allows developers to quickly generate boilerplate code for common patterns, such as MVC controllers, Razor Pages, entity models, and CRUD (Create, Read, Update, Delete) operations against a database. It can be used through the .NET CLI or within Visual Studio, speeding up development by generating the necessary code structure and elements based on the project’s context.

What are the benefits of using Razor Class Libraries (RCLs) in ASP.NET Core?

Razor Class Libraries (RCLs) enable the sharing of Razor views, pages, controllers, and data models across multiple ASP.NET Core web applications. Benefits include:

• Reusability: Promotes DRY (Don’t Repeat Yourself) principles by allowing reuse of UI components and logic.
• Modularity: Enhances application maintainability by encapsulating different functionalities within separate class libraries.
• Simplifies Deployment and Updates: Shared components can be updated across all applications by updating the RCL.

What is the purpose of the IActionResult interface in ASP.NET Core?

The IActionResult interface is used in ASP.NET Core MVC and Razor Pages to represent the result of an action method. It abstracts the way actions return data and allows for a flexible mechanism to return different types of responses (views, file downloads, redirects, HTTP status codes, etc.), making the action methods more modular and testable.

How do you implement background tasks in ASP.NET Core?

Background tasks in ASP.NET Core can be implemented using hosted services with the IHostedService interface or by deriving from the BackgroundService abstract class. These services can run background operations on a timer or in response to some trigger. They are registered in the ConfigureServices method of Startup.cs and are useful for tasks that should occur outside the request processing pipeline, such as background data processing or periodic cleanup tasks.

What is the purpose of the IWebHostBuilder interface in ASP.NET Core?

The IWebHostBuilder interface in ASP.NET Core is used to configure and build an instance of IWebHost. It abstracts the setup of the web server and the hosting environment, allowing developers to configure services, the request processing pipeline, logging, and more. It is typically used in the Program.cs file of an ASP.NET Core application to configure and launch the application’s web server.

In the next article, I will discuss Frequently Asked Top 50 ASP.NET Core Experienced Interview Questions and Answers. In this article, I provided the list of Frequently Asked Top 50 ASP.NET Core Intermediate Interview Questions and Answers. I hope you enjoy this article on ASP.NET Core Intermediate Interview Questions and Answers.

If you want to share any questions and answers, please put them in the comment section, which will benefit others. If you face any questions in the interview that we are not covering here, please feel free to put that question(s) in the comment section, and we will definitely add that question(s) with answers as soon as possible.