ASP.NET Core Web API Basic Interview Questions and Answers

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ASP.NET Core Web API Basic Interview Questions and Answers

In this article, I will discuss the most frequently asked Top 50 ASP.NET Core Web API Basic Interview Questions and Answers. When preparing for an interview focused on ASP.NET Core Web API, it’s crucial to cover a wide range of topics, from basics to advanced features. Here’s a comprehensive list of ASP.NET Core Web API Basic Interview Questions and Answers.

What is ASP.NET Core Web API?

ASP.NET Core Web API is a framework for building HTTP services that can be consumed by various clients, including web browsers, mobile devices, and IoT devices. It allows developers to build lightweight, scalable, and high-performance APIs using the ASP.NET Core framework.

Explain the REST architectural style.

REST (Representational State Transfer) is an architectural style for designing networked applications. It relies on a stateless, client-server communication protocol, typically HTTP, and emphasizes the use of standard HTTP methods (GET, POST, PUT, DELETE) for performing CRUD (Create, Read, Update, Delete) operations on resources. RESTful APIs are designed to be scalable, maintainable, and easily accessible.

What are the main features of ASP.NET Core Web API?

Some of the main features of ASP.NET Core Web API include:

• Built-in support for creating RESTful APIs.
• Unified MVC (Model-View-Controller) and Web API frameworks.
• Cross-platform support, allowing development on Windows, Linux, and macOS.
• Middleware-based pipeline for handling requests and responses.
• Built-in support for dependency injection.
• Integrated support for JSON and XML data formats.
• Support for authentication and authorization using various mechanisms.

Describe HTTP methods and their purpose.

HTTP methods, also known as HTTP verbs, are actions that can be performed on a resource. The main HTTP methods and their purposes are:

• GET: Retrieve data from the server.
• POST: Submit data to the server to create a new resource.
• PUT: Update an existing resource on the server.
• DELETE: Remove a resource from the server.
• PATCH: Apply partial modifications to a resource.
• OPTIONS: Retrieve information about the communication options available for a resource.
• HEAD: Retrieve metadata about a resource without fetching the resource itself.

What is Middleware in ASP.NET Core Web API?

Middleware in ASP.NET Core Web API is software components that are added to the HTTP request pipeline to handle requests and responses. Middleware components are executed in the order they are added to the pipeline and can perform various tasks such as logging, authentication, authorization, exception handling, and content negotiation.

Explain routing in ASP.NET Core Web API.

Routing in ASP.NET Core Web API is the process of matching incoming HTTP requests to the appropriate controller action based on the request URL and HTTP method. Route templates are defined using attributes or convention-based routing, allowing developers to define custom URL patterns for their APIs.

How do you secure ASP.NET Core Web API?

ASP.NET Core Web API can be secured using various mechanisms such as:

• Authentication: Implementing authentication mechanisms like JWT (JSON Web Tokens), OAuth, or OpenID Connect.
• Authorization: Applying authorization policies to restrict access to certain endpoints or resources.
• HTTPS: Enabling HTTPS to encrypt data transmitted between clients and the server.
• CORS (Cross-Origin Resource Sharing): Configuring CORS policies to control access to resources from different origins.
• Data validation and sanitization: Validating and sanitizing input data to prevent security vulnerabilities such as SQL injection and XSS (Cross-Site Scripting).

What is Model Binding in ASP.NET Core Web API?

Model Binding in ASP.NET Core Web API is the process of mapping HTTP request data to parameters of controller action methods or model properties. It automatically binds data from various sources such as query string parameters, route values, and request body, and forms data for the corresponding parameters or model properties based on their names and data types.

What is dependency injection and its benefits?

Dependency Injection (DI) is a design pattern and technique for managing object dependencies in software applications. In ASP.NET Core Web API, DI is built into the framework and allows developers to register and resolve dependencies using built-in container services. The benefits of dependency injection include:

• Improved modularity and maintainability of code.
• Increased testability by enabling easier mocking and unit testing.
• Reduced coupling between components, making the codebase more flexible and easier to refactor.
• Promotes the principle of “Inversion of Control” (IoC), where the control of object creation and lifecycle management is delegated to a container.

How do you handle errors in ASP.NET Core Web APIs?

Errors in ASP.NET Core Web APIs can be handled using various techniques such as:

• Global exception handling: Implementing a global exception filter to catch unhandled exceptions and return appropriate error responses.
• Middleware: Writing custom middleware components to handle specific types of errors and generate error responses.
• Use of status codes: Returning appropriate HTTP status codes (e.g., 400 Bad Request, 404 Not Found, 500 Internal Server Error) to indicate the nature of the error.
• Logging: Logging errors and exceptions to record details for troubleshooting and debugging purposes.
• Error response models: Creating custom error response models to provide additional information about the error to the client.

Explain data annotation in ASP.NET Core Web API.

Data annotations in ASP.NET Core Web API are attributes that can be applied to model properties to specify validation rules, formatting options, and other metadata. Examples of data annotations include [Required], [StringLength], [Range], [RegularExpression], etc. These annotations help in validating and formatting data before it is processed by the API.

How do you perform database migrations in EF Core?

Database migrations in EF Core can be performed using the Entity Framework Core Migrations feature. Developers can use the dotnet ef migrations CLI commands or the Add-Migration and Update-Database commands in the Package Manager Console in Visual Studio to create and apply migrations to the database schema based on changes made to the model classes.

What are action filters?

Action filters in ASP.NET Core Web API are attributes that can be applied to controller actions to add pre-processing or post-processing logic. They allow developers to intercept requests before they reach the controller action or responses before they are sent back to the client. Examples of action filters include AuthorizationFilter, ExceptionFilter, ActionFilter, and ResultFilter.

How do you log information in ASP.NET Core Web API applications?

Logging in ASP.NET Core Web API applications can be done using the built-in logging framework provided by Microsoft.Extensions.Logging namespace. Developers can configure logging providers such as Console, Debug, EventLog, File, etc., in the ConfigureLogging method of Startup class. Logging can be done using the ILogger interface, which allows logging of messages at different log levels such as Information, Warning, Error, Debug, etc.

What is CORS, and how do you enable it?

CORS (Cross-Origin Resource Sharing) is a security feature implemented by web browsers that restricts web applications running on one domain from making requests to another domain. In ASP.NET Core Web API, CORS can be enabled by configuring CORS policies in the ConfigureServices method of the Startup class using the AddCors method. CORS policies can be configured to allow or restrict cross-origin requests based on specified origins, HTTP methods, headers, etc.

How do you implement API versioning in ASP.NET Core Web API?

API versioning in ASP.NET Core Web API can be implemented using various approaches such as URI-based versioning, query string-based versioning, header-based versioning, or using a custom media type. Developers can use the Microsoft.AspNetCore.Mvc.Versioning package to version APIs and configure versioning options in the ConfigureServices method of the Startup class.

What are environment variables, and how are they used?

Environment variables are dynamic variables that are used to configure application behavior based on the runtime environment. In ASP.NET Core Web API, environment variables can be used to specify configuration settings, such as database connection strings, API keys, logging levels, etc., that may vary across different environments, such as development, staging, and production.

How do you use appsettings.json for configuration?

In ASP.NET Core Web API, configuration settings can be stored in the appsettings.json file, which is a JSON formatted file that contains key-value pairs of configuration settings. The appsettings.json file is loaded and parsed during application startup, and the configuration settings can be accessed using the IConfiguration interface. Developers can use the ConfigureAppConfiguration method in the Startup class to load additional configuration sources such as environment variables, command-line arguments, etc.

What is Swagger, and why is it used?

Swagger is a tool for documenting and testing APIs. It generates interactive API documentation from API metadata such as OpenAPI (formerly Swagger) specifications, allowing developers to explore and test API endpoints without writing any client code. In ASP.NET Core Web API, Swagger can be integrated using the Swashbuckle.AspNetCore package to automatically generate Swagger documentation for the API and expose a Swagger UI for testing endpoints.

Explain the purpose of the [ApiController] attribute.

The [ApiController] attribute is used to indicate that a controller class is an API controller in ASP.NET Core Web API. When applied to a controller class, it enables various behaviors such as automatic model validation, automatic HTTP 400 responses for invalid requests, and binding source parameter inference. It also applies a set of conventions for API behavior, such as handling of HTTP methods and responses, which simplifies API development and improves consistency.

How do you manage application settings and configurations?

Application settings and configurations in ASP.NET Core Web API can be managed using the appsettings.json file, environment variables, command-line arguments, and other configuration sources. The settings can be accessed using the IConfiguration interface and can be injected into classes using dependency injection.

What is the significance of Program.cs in ASP.NET Core Web API?

Program.cs is the entry point of an ASP.NET Core Web API application. It contains the Main method, which sets up the host for the application and configures services and middleware. It is responsible for configuring the application’s host, logging, dependency injection, and starting the web server.

How do you create and use custom middleware in ASP.NET Core Web API?

Custom middleware in ASP.NET Core Web API can be created by implementing a class with a method that conforms to the RequestDelegate delegate signature. The custom middleware can perform tasks such as request processing, response modification, error handling, etc. It is added to the middleware pipeline using the UseMiddleware extension method in the Configure method of the Startup class.

What are the differences between app.Use vs. app.Run?

• app.Use: Adds middleware to the request processing pipeline. It can handle the request itself or pass it to the next middleware in the pipeline.
• app.Run: Adds terminal middleware to the request processing pipeline. It must be the last middleware added and is responsible for generating a response or terminating the request pipeline.

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

File uploads in ASP.NET Core Web API can be handled by using the IFormFile interface to represent uploaded files in controller action parameters. The files can be received as part of a multipart/form-data request and processed using model binding or directly accessing the request body. Additionally, developers can configure the maximum file size and other upload-related settings in the Startup class.

How do you implement authentication using Identity in ASP.NET Core Web API?

Authentication using Identity in ASP.NET Core Web API can be implemented by configuring the Identity services in the ConfigureServices method of the Startup class. This involves setting up identity options, specifying the user and role entity types, configuring authentication schemes, and enabling authentication middleware. Once configured, developers can use authentication attributes or middleware to secure API endpoints.

What is JWT, and how is it used in ASP.NET Core Web API?

JWT (JSON Web Token) is a compact, URL-safe means of representing claims to be transferred between two parties. In ASP.NET Core Web API, JWT is commonly used for authentication and authorization purposes. It allows users to securely transmit information between the client and server as a JSON object, typically containing user identity information and additional metadata.

Explain the role of HTTPS in security.

HTTPS (Hypertext Transfer Protocol Secure) is the secure version of HTTP and provides encrypted communication between a client and a server. In ASP.NET Core Web API, HTTPS is crucial for securing sensitive data transmitted over the network, such as authentication tokens, user credentials, and other sensitive information. It protects against eavesdropping, man-in-the-middle attacks, and data tampering.

How do you use attribute routing in ASP.NET Core Web API?

Attribute routing in ASP.NET Core Web API allows developers to define routes for controller actions using attributes. This involves applying the [Route] attribute to controller classes or action methods to specify the route template. Attribute routing provides a more declarative and flexible way to define routes compared to convention-based routing.

How do you implement social authentication?

Social authentication in ASP.NET Core Web API can be implemented using OAuth or OpenID Connect protocols with external identity providers such as Google, Facebook, Twitter, etc. Developers can use third-party authentication middleware like Microsoft.AspNetCore.Authentication.Google, Microsoft.AspNetCore.Authentication.Facebook, etc., to configure authentication options and handle the authentication flow with the external providers.

How do you handle real-time web functionalities?

Real-time web functionalities in ASP.NET Core Web API can be achieved using technologies such as SignalR. SignalR is a library that simplifies adding real-time web functionality to applications by providing bi-directional communication between clients and servers. It allows users to push content from the server to connect clients instantly, enabling features like chat applications, live updates, notifications, etc.

How do you implement global exception handling?

Global exception handling in ASP.NET Core Web API can be implemented using middleware or filters. Middleware can be used to catch exceptions globally and return appropriate error responses. Alternatively, developers can implement an exception filter by creating a class that implements the IExceptionFilter interface and registering it globally using the services.AddMvc(options => options.Filters.Add<ExceptionFilter>()) method in the Startup class.

What is the difference between IActionResult and ActionResult?

IActionResult is an interface representing the result of an action method in ASP.NET Core Web API. ActionResult is a base class that implements IActionResult. The main difference is that ActionResult provides additional helper methods for creating various types of action results, such as Ok, BadRequest, NotFound, etc., whereas IActionResult is an interface that defines the contract for all action results.

How do you optimize API performance?

API performance optimization in ASP.NET Core Web API can be achieved through various techniques such as:

• Implementing caching mechanisms to reduce database or computation overhead.
• Using asynchronous programming to improve scalability and responsiveness.
• Optimizing database queries and reducing data transfer.
• Minimizing payload size by using compression techniques like gzip.
• Implementing rate limiting and throttling to prevent abuse and ensure fair usage of resources.
• Utilizing CDN (Content Delivery Network) to serve static content.
• Profiling and performance testing to identify bottlenecks and areas for improvement.

What is the difference between AddMvc() and AddMvcCore()?

• AddMvc(): This method adds all the necessary services for MVC (Model-View-Controller), including filters, formatters, model binders, and view engines. It configures MVC options and adds all built-in MVC services required for full MVC functionality.
• AddMvcCore(): This method adds only the minimal set of services required for MVC, excluding features like Razor view engine, model validation, and other higher-level MVC functionalities. It is suitable for building lightweight APIs without the overhead of full MVC.

How do you manage sessions in ASP.NET Core Web API?

ASP.NET Core Web API typically does not use session state because it’s designed for stateless communication. However, if session management is required, developers can use distributed caching or session management middleware provided by ASP.NET Core. This involves configuring session services in the Startup class and using the HttpContext.Session property to access and manipulate session data.

What are dependency injection scopes?

Dependency injection scopes in ASP.NET Core Web API define the lifespan of a service instance created by the dependency injection container. There are three built-in scopes:

• Transient: A new instance of the service is created every time it is requested.
• Scoped: A single instance of the service is created per request scope.
• Singleton: A single instance of the service is created for the lifetime of the application.

How do you implement API rate limiting?

API rate limiting in ASP.NET Core Web API can be implemented using middleware or third-party libraries such as AspNetCoreRateLimit. Developers can configure rate-limiting policies based on IP address, client ID, or request path, specifying limits for the number of requests per time interval. The middleware intercepts requests and enforces rate limits, returning appropriate HTTP status codes (e.g., 429 Too Many Requests) when the limit is exceeded.

What are the best practices for API design in ASP.NET Core Web API?

Some best practices for API design in ASP.NET Core Web API include:

• Using meaningful and consistent resource naming conventions (RESTful principles).
• Implementing versioning to manage changes and updates to the API.
• Designing predictable and consistent URIs.
• Leveraging HTTP methods and status codes appropriately.
• Providing comprehensive and clear documentation using tools like Swagger/OpenAPI.
• Securing sensitive data and endpoints using authentication and authorization mechanisms.
• Optimizing performance by minimizing payload size and utilizing caching mechanisms.

How do you create a simple Web API in ASP.NET Core?

To create a simple Web API in ASP.NET Core, you can follow these steps:

• Create a new ASP.NET Core Web API project using Visual Studio or the dotnet new webapi command.
• Define a controller class with action methods to handle HTTP requests.
• Configure routing in the Startup class to map incoming requests to controller actions.
• Implement business logic and data access code within the controller actions.
• Run the application and test the API endpoints using tools like Postman or Swagger UI.

What are the advantages of using ASP.NET Core for Web API development?

Some advantages of using ASP.NET Core for Web API development include:

• Cross-platform compatibility, allowing development on Windows, Linux, and macOS.
• High performance and scalability.
• Built-in support for dependency injection and middleware.
• Unified MVC and Web API frameworks.
• Integrated support for modern web standards like WebSockets and HTTP/2.
• Easy integration with cloud platforms like Azure.
• Open-source and actively maintained by Microsoft with strong community support.

Explain routing in ASP.NET Core Web API.

Routing in ASP.NET Core Web API maps incoming HTTP requests to the appropriate action methods in controllers based on the URL pattern. Routing can be configured using attributes on controller classes and action methods or by convention-based routing in the Startup class. Routes can include placeholders for route parameters, allowing dynamic routing based on the values passed in the URL.

How do you return data from a Web API action?

Data can be returned from a Web API action method using the ActionResult or specific result types such as OkObjectResult, NotFoundResult, BadRequestResult, etc. These result types allow different HTTP status codes and data to be returned. Additionally, data can be returned directly from action methods as objects, which are automatically serialized to JSON or XML based on the client’s request format.

What is JSON and XML serialization in Web API?

JSON (JavaScript Object Notation) and XML (eXtensible Markup Language) serialization in Web API refers to the process of converting .NET objects into JSON or XML format for transmission over the network. ASP.NET Core Web API automatically handles the serialization and deserialization of objects based on the content type specified in the request headers. JSON is commonly used for its simplicity and efficiency in data exchange between client and server.

What is dependency injection, and what is its importance in ASP.NET Core Web API?

Dependency injection (DI) is a design pattern used to achieve loose coupling between components by injecting dependencies into a class rather than creating them internally. In ASP.NET Core Web API, DI is built into the framework and is used to inject services such as repositories, logging, configuration, etc., into controller classes and other components. DI promotes modularity, testability, and maintainability of code.

Explain the concept of Middleware in the ASP.NET Core Web API request pipeline.

Middleware in ASP.NET Core Web API is software components that are added to the HTTP request pipeline to handle requests and responses. Middleware components can intercept requests and responses, perform operations such as logging, authentication, authorization, exception handling, etc., and pass control to the next middleware in the pipeline. Middleware allows developers to modularize and reuse components in the request processing pipeline.

How do you enable CORS in ASP.NET Core Web API?

CORS (Cross-Origin Resource Sharing) in ASP.NET Core Web API can be enabled by configuring CORS policies in the ConfigureServices method of the Startup class using the AddCors method. Developers can specify allowed origins, HTTP methods, headers, and other settings to control access to resources from different origins. CORS policies can be applied globally or to specific controllers and actions using the EnableCors attribute.

What is Swagger, and how do you implement it in ASP.NET Core Web API?

Swagger is a tool for documenting and testing APIs. In ASP.NET Core Web API, Swagger can be implemented using the Swashbuckle.AspNetCore package. It automatically generates interactive API documentation from API metadata such as OpenAPI (formerly Swagger) specifications, allowing developers to explore and test API endpoints without writing any client code. Swagger UI provides a user-friendly interface for interacting with the API.

Describe the process of securing a Web API with JWT.

Securing a Web API with JWT (JSON Web Tokens) involves the following steps:

• Issuing JWT tokens to authenticated users upon successful login.
• Sending the JWT token with subsequent requests from the client.
• Validating the JWT token on the server to ensure its authenticity and integrity.
• Authorizing access to protected resources based on the claims present in the JWT token.
• Configuring authentication middleware in the Startup class to validate JWT tokens and authenticate users.

How do you handle exceptions in ASP.NET Core Web API?

Exceptions in ASP.NET Core Web API can be handled using middleware or filters. Middleware can be used to catch exceptions globally and return appropriate error responses. Alternatively, developers can implement an exception filter by creating a class that implements the IExceptionFilter interface and registering it globally using the services.AddMvc(options => options.Filters.Add<ExceptionFilter>()) method in the Startup class. Additionally, specific exception-handling logic can be applied within individual action methods using try-catch blocks.

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

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