.NET Core Interview Question & Answers
Tags: csharp, dotnet, career, programming
Published: 2023-10-11 09:52:01

Dive into the world of contemporary programming as we untangle some of the most commonly asked **dotnet core interview questions and answers**!

Staying up-to-date with the evolution of technology can be a demanding task, but not if you’re provided with clear explanations and useful insights. In this chunk of knowledge, we’ll delve deeply into the key aspects of .NET Core, allowing you to showcase your expertise and ace your next interview.

Whether you’re an aspiring programmer or an experienced developer revisiting your core dotnet interview know-how, this right here is your invaluable resource!

## How does Dependency Injection work in .NET Core?

### Answer

In .NET Core, Dependency Injection (DI) is a technique whereby one class (or module) outsources the creation of its dependencies to an external framework instead of handling them itself.

Built-in DI is a significant aspect of .NET Core. It comes with integrated support for dependency injection, unlike the previous versions, where we had to rely on external libraries like AutoFac, Ninject, Unity, etc.

Here is a simple example:

```csharp
public class SampleClassA: ISampleClassA
{
    private readonly ISampleClassB _sampleClassB;
    public SampleClassA(ISampleClassB sampleClassB)
    {
        _sampleClassB = sampleClassB;
    }
}
```

In this case, `SampleClassA` depends on `ISampleClassB`. To inject `ISampleClassB` into `SampleClassA`, you need to register these classes in your `Startup.cs` file:

```csharp
public void ConfigureServices(IServiceCollection services)
{
    services.AddTransient<ISampleClassA, SampleClassA>();
    services.AddTransient<ISampleClassB, SampleClassB>();
}
```

When `SampleClassA` is created, .NET Core automatically creates an instance of `SampleClassB` and injects it into the constructor.

## Can you explain how .NET Core’s performance compares to Node.js?

### Answer

In terms of performance, both .NET Core and Node.js have their strengths and weaknesses. Performance can also be relative based on the specific workload and requirements of the application, but here are some general insights:

-   **Response Time**: .NET Core generally holds an edge over Node.js in raw response time. .NET Core has been designed to deal with high-performance servers and optimized accordingly.
-   **Concurrent Request Handling**: Node.js uses a single-threaded, event-driven architecture that is efficient for handling high volumes of concurrent, IO-intensive workloads. In contrast, .NET Core uses a multi-threaded approach, which can lead to higher resource consumption under heavy loads but can handle CPU-intensive workloads more efficiently.
-   **Throughput**: In most cases, .NET Core exhibits high throughput rates compared to Node.js due to its inherent design and the optimization done by the JIT compiler.

Remember, while these are some of the general observations, the real-life performance of an application will depend on various factors, including how well the code is written and optimized.

## How do you manage cross-platform targeting in a .NET Core project?

### Answer

.NET Core projects are capable of targeting multiple platforms including Windows, Linux, and macOS. This can be managed through the project file (`*.csproj`).

First, the Target Framework Moniker (TFM) determines the APIs that you have access to. It is possible to specify multiple target frameworks and libraries depending on your application needs. The selected framework will dictate which APIs your code can call.

Here is an example where the project targets .NET Core 3.1 and .NET Standard 2.0:

```csharp
<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFrameworks>netcoreapp3.1;netstandard2.0</TargetFrameworks>
  </PropertyGroup>

</Project>
```

You need to be aware of any breaking changes or incompatible APIs when targeting multiple platforms. It is also possible to handle divergent code with the help of preprocessor directives.

## What are the main advantages of using Entity Framework Core over Entity Framework 6.x in a .NET Core application?

### Answer

Entity Framework Core (EF Core) is a lightweight, extensible, open-source, and cross-platform version of the popular Entity Framework data access technology. Here are the main advantages of using EF Core:

-   **Cross-Platform**: EF Core works with .NET Core, which makes it possible to run on any platform that .NET Core supports.
-   **Improved Performance**: Compared to EF 6.x, EF Core provides better performance because of its optimized query generation and processing.
-   **Modular Design**: EF Core is more modular, which means you can include only the necessary packages your application needs, leading to less clutter and overhead.
-   **Built-In Dependency Injection**: EF Core supports the new .NET Core dependency injection feature out of the box.
-   **Flexibility and Extensibility**: EF Core is designed to be flexible and extensible, allowing developers to adapt the framework to their specific needs.

## How does Kestrel server work in the .NET Core environment and how does it differ from other web servers?

### Answer

Kestrel is a cross-platform web server built for .NET Core based applications. It is based on a libuv library, an asynchronous I/O-based model used by Node.js. Kestrel can also be used in combination with a reverse proxy server such as Apache, Nginx, or IIS, which provides an additional layer of configuration, security, and load balancing.

Here are the key differences between Kestrel and other web servers such as IIS and Http.sys:

-   **Cross-Platform**: Unlike IIS and Http.sys, which are Windows-specific, Kestrel can run on multiple operating systems thanks to its integration with .NET Core.
-   **Performance**: Kestrel is designed to be fast and has been heavily optimized for performance. It demonstrates high throughput and has a lower request latency than traditional IIS.
-   **Stand-Alone or with Reverse Proxy**: Kestrel can be used as a stand-alone web server or with a reverse proxy. Using it with a reverse proxy can help protect the application from potential vulnerabilities.
-   **In-Process or Out-Of-Process Models**: With the advent of .NET Core 2.2 and 3.0, Kestrel can be used in both in-process and out-of-process hosting models, providing flexibility in how your application is hosted.

Overall, when considering a web server for hosting .NET Core applications, Kestrel provides a high-performance, cross-platform, and flexible option that aligns well with the objectives of .NET Core.

___

Moving smoothly from servers to application patterns, let’s discuss another fundamental topic that often spices up **net core questions for interviews** – the Repository pattern.

Certainly, transitioning from the way Kestrel servers operate in .NET Core to the application of patterns in Entity Framework Core might seem like a leap. But don’t fret, as we’ll guide you through the interconnected world of .NET Core with simple explanations and concise examples.

___

## How would you implement the Repository pattern in a .NET Core application using Entity Framework Core?

### Answer

To implement the Repository pattern in a .NET Core application using Entity Framework Core, you could follow these general steps:

-   **Create an interface for repositories:** Each repository should have its unique interface defining the operations it supports. For example, in a student management system, a typical IRepository interface might include methods for GetAll, GetById, Insert, Update, and Delete.
-   **Implement repository interfaces:** Write a class that implements each interface, providing the logic for the defined operations. Entity Framework Core’s DbContext provides the functionality to handle these operations.
-   **Create a UnitOfWork class:** Unit of Work is another pattern that’s often used with Repository. It groups one or more operations (like reading, insertion, or deletion) into a single transaction. In the context of Entity Framework Core, your DbContext class would act as your unit of work.
-   **Use dependency injection to provide instances of your repositories to controllers:** .NET Core has built-in support for dependency injection. You can provide your DbContext and repository classes in ConfigureServices method of your Startup class.

Here is a simple example of what the repository class might look like:

```csharp
public class Repository<T> : IRepository<T> where T : class{
    private readonly DbContext _dbContext;
    public Repository(DbContext dbContext){
        _dbContext = dbContext;
    }
    public IEnumerable<T> GetAll(){
        return _dbContext.Set<T>().ToList();
    }
    //... other methods
}
```

## How do you handle exceptions globally in an ASP.NET Core Web API project?

### Answer

Global [exception handling](https://www.bytehide.com/blog/5-good-practices-for-error-handling-in-c) in ASP.NET Core can be achieved using middleware. The ideal place to handle exceptions is in the middleware pipeline so that it is separate from your application logic, and can trap any unhandled exceptions.

One of the most effective ways is to use the built-in `UseExceptionHandler` middleware which captures synchronous and asynchronous exceptions. With this middleware, you can redirect to an error handling route or render an error response directly.

```csharp
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    else
    {
        app.UseExceptionHandler("/api/Error");
    }

    //... rest of the middleware
}
```

In the above code, when an exception is raised it is handled by the “/api/Error” route.

Another method of handling global exceptions is using `UseDeveloperExceptionPage` middleware which provides detailed exception information in the local development environment.

## What are the significant differences between .NET Core 2.x and .NET Core 3.x?

### Answer

There are a number of significant differences between .NET Core 2.x and .NET Core 3.x:

**Desktop Development:** .NET Core 3 introduced support for Windows Desktop Applications (Windows Forms and WPF). This feature was not available in .NET Core 2.

**New JSON APIs:** .NET Core 3.0 introduced new built-in JSON APIs that are high-performance and low allocation, making them significantly faster than JSON.NET.

**HTTP/2 Support:** In .NET Core 3, built-in support for HTTP/2 was added.

**Improved performance:** Continuous enhancements were made to improve the performance of .NET Core including less memory consumption and faster application startup times.

**gRPC Services:** .NET Core 3.x introduced support for gRPC, a modern open-source high-performance RPC framework.

**Support for ARM64:** .NET Core 3.0 added support for ARM64-based processors.

## Can you explain the steps involved in configuring and working with Azure Active Directory in .NET core?

### Answer

Azure Active Directory (Azure AD) provides an easy way for businesses to manage identity and access, both in the cloud and on-premises. You can use it to add sign-in functionality and regulate access to your .NET Core applications. Here are the essential steps to configure and work with Azure AD in a .NET Core application:

**Register your application with your Azure AD tenant:**

-   Log in to the Azure portal.
-   Click Azure Active Directory, and then click App registrations to open the [list](https://www.bytehide.com/blog/list-csharp) of registered applications.
-   Click New registration, and provide a suitable name for your application.
-   In the Redirect URI field, enter the base URL for your application.

**Configure your .NET Core application to use Azure AD:**

Open your application settings in the Azure portal, copy the Directory (tenant) ID and Application (client) ID, and then use them to configure the authentication in your .NET Core application.

```csharp
public void ConfigureServices(IServiceCollection services)
{
    services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
        .AddJwtBearer(options =>
        {
            options.Authority = "<Directory (tenant) ID>";
            options.Audience = "<Application (client) ID>";
        });

    services.AddControllers();
}
```

**Protect your application’s routes:**

```csharp
[Authorize]
public class SecureController : Controller
{
  //... controller logic here
}
```

**Use Azure AD as user store:**

You can use Azure AD to store and manage users for your .NET Core application.

## How to do database migrations in Entity Framework Core?

### Answer

Entity Framework Core (EF Core) includes a feature called Migrations that allows you to make changes to your model and then propagate those changes to your database schema. Here’s a basic overview of performing a migration:

**1\. Install the necessary packages:** EF Core requires certain NuGet packages to perform migrations. Make sure you have the basic Entity Framework Core and EF Core tools packages installed in your project.

**2\. Create a new Migration:** Use the `Add-Migration` command and provide a name for your migration. This creates a new class in your Migrations folder that contains the changes to be made to the database schema.

```csharp
Add-Migration MyFirstMigration
```

**3\. Update the database:** Use the `Update-Database` command. This applies any pending migrations on the database. EF Core creates the database if it does not exist.

```csharp
Update-Database
```

You may opt to provide a specific migration name if you want to update the database to a specific migration rather than the latest.

Remember to treat migrations as a part of your codebase. They need to be kept under source control and applied as part of your deployment process. Well-managed migrations are key to dealing with evolving database schemas.

___

We’ve had a comprehensive understanding of how to conduct database migrations in Entity Framework Core so far. But what about real-time communication in web applications?

As the terrain of **dotnet core interview questions and answers** is vast and varied, let’s shift our sails and explore the realm of SignalR and its indispensable role in the .NET Core universe.

Real-time communication is a crucial cog in the wheel of interactive and highly responsive applications, so stick around as we dive deeper!

___

## How can you explain SignalR’s role in .NET Core and how it enhances real-time communication in web applications?

### Answer

SignalR is a library in .NET Core used to facilitate real-time communication between server and client. It uses several techniques under the hood to maintain a persistent connection between the client and the server. This connection allows real-time communication with high-frequency updates.

SignalR uses WebSockets, Long Polling, Server-Sent Events, and others to maintain this connection, choosing the best available transport method based on the client and server capabilities.

In effect, SignalR simplifies the process of creating real-time, responsive web applications. It’s widely used in applications where high frequency updates are required, such as live chat, gaming, real-time dashboards, and others.

## How do you secure .NET Core Web API using IdentityServer4?

### Answer

IdentityServer4 is an OpenID Connect and OAuth 2.0 framework for .NET Core, which can be used to secure your .NET Core Web API.

To do this, you would need to install and configure IdentityServer4 in your application. This will involve creating the necessary client configurations, defining scopes, and securing your API endpoints.

Here is a basic overview of the steps:

-   Install the IdentityServer4 package in your application
-   Create an IdentityServer service and configure its options in your Startup class. This includes setting up your resources, clients, and scopes.
-   Add the authentication middleware to your application pipeline, specifying the IdentityServer authentication handler.
-   Decorate your API actions or controllers with the `[Authorize]` attribute to ensure they are secured.

It’s important to remember that securing your API requires a clear understanding of authentication and authorization concepts, as well as the protocols used by IdentityServer4 (OpenID Connect and OAuth 2.0).

## How would you manage configurations in a .NET Core application when moving from development to production?

### Answer

.NET Core provides an elegant solution to managing configurations across different environments through the use of configuration providers.

For managing configuration, you can use the appsettings.json file, which is the default file read by .NET Core application. Moreover, you can have dedicated configuration files for each environment, such as appsettings.Development.json or appsettings.Production.json, giving you the chance to override the default settings.

Here are some steps you could take:

-   Use different appsettings.{Environment}.json files to store environment-specific configurations.
-   Use the environment variable configuration provider to set environment-specific settings. The settings set by this provider take precedence over those set in the appsettings.json.
-   Use the `IConfiguration` interface in your classes to access configured settings.

Remember to exclude sensitive data like connection strings and application secrets from source control by using secure methods like user secrets or Azure Key Vault.

## How does the out-of-the-box logging framework in .NET Core work?

### Answer

With .NET Core, you get an in-built, easy-to-use logging API which supports a variety of built-in and third-party logging providers. It provides various logging levels like Trace, Debug, Information, Warning, Error, and Critical.

The steps to add logs to a .NET Core application using this framework are as follows:

-   Inject the `ILogger<T>` dependency in your class, where `T` is the class into which `ILogger<T>` is injected.
-   Use the provided methods (`LogDebug`, `LogInformation`, `LogWarning`, `LogError`, `LogCritical`) to log messages at different levels.

You can configure these log levels and logging output targets in the appsettings.json or in your code. The framework automatically reads from the configuration settings at runtime.

## How would you implement CQRS in a .NET Core application?

### Answer

Command Query Responsibility Segregation (CQRS) is a pattern in which read operations (queries) and write operations (commands) are separated, improving performance, scalability, and security.

To implement this in .NET Core:

-   Create two separate models: a write model (for commands) and a read model (for queries).
-   Define distinct interfaces/classes for your commands and queries.
-   Use the MediatR library, which provides a straightforward way to implement the CQRS pattern. You define your queries and commands as Request/Notification handlers.
-   For the read operations, you can design the models according to the needs of the client application, while the write model can be closer to the business/domain model.

Remember, while CQRS can provide performance and scalability benefits, it adds complexity to the application and should be used wisely, preferentially in more complex scenarios where these benefits are significant.

___

Having understood how to implement Command Query Responsibility Segregation (CQRS) in a .NET Core application, it’s time to transition towards microservices. The jump may seem wide, but it’s all threads in the same vast tapestry of **core dotnet interview questions**.

In the complex world of .NET Core ecosystems, knowledge of microservices becomes incredibly pertinent. So, let’s delve into the support provided by .NET Core for the development of microservices and how they efficiently manage a large application’s complex business requirements.

___

## How does .NET Core support the development of microservices?

### Answer

.NET Core supports the development of microservices by several ways:

-   **Cross-platform support** – .NET Core supports the development and deployment of applications on several operating systems including Windows, Linux, and macOS. This flexibility is crucial for microservices architecture as it allows services to be deployed on a variety of platforms.
-   **Easily integrated with Docker** – Docker is a popular platform used to deploy applications, and .NET Core has excellent support for Docker. It is possible to create a Dockerfile for an application, which makes it easy to build and run the application inside a Docker container.
-   **Independent Deployment** – Each microservice can be developed, tested and deployed independently of others. Microservices can also have their own databases and develop their own individual business capabilities.
-   **Scalability** – Microservices developed with .NET Core can be easily scaled out or in, depending on the demand. They don’t have to share server resources and can be scaled independently.
-   **Resiliency** – .NET Core and the use of microservices provide for each service to be able to handle and respond to failure. If a microservice fails, it won’t crash the whole system.

## How is routing implemented in ASP.NET Core MVC compared to ASP.NET MVC?

### Answer

There are several differences in how routing is handled in ASP.NET Core MVC compared to ASP.NET MVC.

-   In ASP.NET MVC, routing was handled through a central `RouteConfig` file that includes rules for each controller and action method. These routing rules can be either attribute-based or convention-based.
-   On the other hand, ASP.NET Core MVC uses middleware for routing. It provides two types of routing methodologies – convention-based routing and attribute routing. All the routing information is configured in the `Startup.cs` file.
-   In ASP.NET Core MVC, we also have a new feature, Routing to Razor Pages. Razor Pages are a new aspect of ASP.NET Core MVC that allow you to create page-based programming model.
-   Additionally, ASP.NET Core MVC supports route constraints, which weren’t available in ASP.NET MVC. Route constraints let you restrict how the parameters in the route template are matched.

## What are some of the best techniques for optimizing performance in .NET Core applications?

### Answer

Optimizing performance in .NET Core applications could involve several techniques:

-   **Caching**: It’s about storing data somewhere for future use to speed up the application. .NET Core provides support for several different types of caching including in-memory caching, distributed caching, and response caching.
-   **Asynchronous Programming**: Use the async and [await](https://www.bytehide.com/blog/await-csharp) keywords to write asynchronous code that’s easier to read, write and manage.
-   **Pooling**: Techniques such as Object Pooling or Connection Pooling can be used to recycle objects or connections instead of creating and destroying them frequently.
-   **Optimization of Data Access**: Minimize the amount of data that you send over the network and reduce the number of server round trips.
-   **Use of Middleware**: Middleware components are used to handle requests and responses. Ensure that unnecessary middleware components are not registered.

## Can you explain some possible strategies for managing session state in a distributed .NET Core application?

### Answer

Managing session state in a distributed .NET Core application generally involves either a server-side or client-side session management approach.

-   **Server-side session management**: It store session data on the server. This strategy involves storing the session state in a database or in-memory data store like Redis. This allows applications running on multiple servers to have access to the shared session data.
-   **Client-side session management**: In this strategy, the session state is stored in a client side, usually in cookies or in local storage. This strategy eliminates the need to store session data on the server, which can be especially useful in applications with a large number of users.
-   **Distributed Cache Session Management**: ASP.NET Core provides IDistributedCache interface that you can use to store your session state.

Remember to always secure session data, especially when incorporating client-side session management strategies.

## How would you approach error handling and debugging in a distributed .NET Core application with multiple microservices?

### Answer

Handling errors and debugging in a distributed .NET Core application with multiple microservices can be challenging. Some of the strategies include:

-   **Centralized Logging**: All microservices should send their logs to a centralized place where they are collated and indexed. This allows you to search and visualize logs from all services at one place.
-   **Use of Correlation IDs**: Correlation IDs are unique identifiers that are assigned to a request. This ID is then passed to all the services that are involved in handling that request. This allows you to trace the entire chain of requests and responses.
-   **Health Check APIs**: Health check APIs can be implemented to monitor the status of the microservices. They can report metrics like uptime, CPU usage, memory usage etc.
-   **Exception Handling Middleware**: You can create a middleware that wraps around every microservice request. If an exception occurs during the execution of the request, this middleware will catch the exception and respond with a meaningful error message.
-   **Use a Distributed Tracing System**: It collects data and metrics from each microservice, then collates that data into a comprehensive, visual overview of your system’s performance.

Remember that in a microservices architecture errors should be handled at the service level. Each service should handle its own exceptions and return a suitable error message or response code.

Wrapping up our deep dive into **net core questions for interviews**, we hope you found the thorough explanations and code examples enlightening.

Remember, the journey of a thousand miles begins with a single step, and every complex problem can be broken down into simple, easy-to-understand blocks. And that’s precisely what our exploration of the .NET Core environment aimed to do.

So whether you’re preparing for your next interview or simply seeking to solidify your .NET Core understanding, keep this guide in your arsenal!

**Until next time, happy coding!**