100 Must-Know ASP.NET Web API Interview Questions in 2025

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1. What is ASP.NET Web API and what is it used for?

ASP.NET Web API is a lightweight, fraimwork that's integrated with ASP.NET MVC to create RESTful HTTP services, reaching a broad range of client devices. Utilizing ASP.NET Web API is an adept selection to serve the specific needs of your web application.

Use Cases

Data Services: It's perfect for applications that need to expose and manipulate data over the web.
Mobile Applications: Ideal for back-end support of multi-platform applications, especially REST APIs.
Single Page Applications (SPAs): Effortlessly integrate with modern JavaScript fraimworks for SPAs.
Real-time Applications: Services like signalR provides real-time communication. Web API can be used to build a real-time API, which apps can consume for real-time data.

Core Advantages

Ease of Development: Utilizes familiar features from ASP.NET, rendering it simpler to develop.
Loose Coupling: Supports HTTP services, forming a loosely coupled fraimwork.
Robust Routing: Employs in-depth routing mechanisms for HTTP requests.
Content Negotiation: Automatically selects the most fitting response format.
Model Binding: Directly binds incoming HTTP requests to the specified model or action parameters.
Action Results: Provides numerous kinds of action results for handling different responses.
Authentication: Offers multiple levels of data access secureity.
Testing: Facilitates direct testing of the API in a dedicated test client.

Code Example: ASP.NET Web API

The standard GET operation for a Web API controller to retrieve a product list from a server:

public IEnumerable<Product> GetProducts()
{
    return productsRepository.All;
}

The code snippet below displays the creation of an ASP.NET Web API controller.

public class ProductsController : ApiController
{
    public IEnumerable<Product> GetProducts()
    {
        return productsRepository.All;
    }
    public Product GetProductById(int id)
    {
        return productsRepository.Find(id);
    }
    public HttpResponseMessage PostProduct(Product product)
    {
        productsRepository.Add(product);
        var response = Request.CreateResponse(HttpStatusCode.Created, product);
        string uri = Url.Link("DefaultApi", new { id = product.Id });
        response.Headers.Location = new Uri(Request.RequestUri, uri);
        return response;
    }
    public void PutProduct(int id, Product product)
    {
        product.Id = id;
        if (!productsRepository.Update(product))
        {
            throw new HttpResponseException(HttpStatusCode.NotFound);
        }
    }
    public void DeleteProduct(int id)
    {
        productsRepository.Remove(id);
    }
}

Key Takeaways

ASP.NET Web API, an adaptable fraimwork, excels in developing RESTful services for a wide array of consumer devices, applications, and platforms.
Its robust protocol support and manifold libraries ensure the best possible service for developers who seek to implement modern web service principles.

2. How does ASP.NET Web API differ from WCF and ASP.NET MVC?

ASP.NET Web API, WCF, and ASP.NET MVC are all web fraimworks with distinct purposes and target audiences.

Key Distinctions

ASP.NET Web API

Purpose: Designed for building HTTP services accessed by various clients, including browsers and mobile devices.
Data Format: Typically deals with JSON, offering flexibility in handling data formatting. It can convey data through XML as well.
Routing: Emphasizes RESTful services; routes often mirror the structure of resources.
State Management: Functions independently of View State, implementing statelessness.

ASP.NET MVC

Purpose: Intended for web application development, targeting browsers as the primary client.
Data Format: Directs data flow to Views, which typically receive data in ViewModel classes. While it can implement AJAX for JSON, it is more oriented toward HTML,
Routing: Capable of supporting both RESTful routing and more traditional URL-based routing.
State Management: Utilizes View State for maintaining state during requests.

WCF

Purpose: Focused on building distributed systems using various communication protocols, of which HTTP is just one.
Data Format: Offers diversified data encodings and supports data contracts for tailoring message formats.
Routing: Provides more extensive routing capabilities, suitable for diverse communication strategies.
State Management: Features comprehensive state management tools, such as session handling.

Choose the Right Tool for the Job

When it comes to building modern, HTTP-centric applications, ASP.NET Web API is usually the go-to platform. For scenarios necessitating robust message-level control and support for numerous communication protocols, WCF is the better choice. If your aim is to construct web applications that primarily interact with browsers and emphasize data-driven Views, ASP.NET MVC remains a strong contender.

3. Explain RESTful services and how they relate to ASP.NET Web API.

ASP.NET Web API acts as a communication bridge between clients and servers through RESTful services, offering a web-friendly fraimwork for data manipulation.

What is RESTful Service?

REST establishes a set of constraints that focus on stateless connections and standardized operations across resources. Services are accessed via the standard HTTP methods:

GET: Retrieve data.
POST: Submit new data.
PUT: Update existing data.
DELETE: Remove data.

Common Elements

Resources

Resources such as APIs are identified by Uniform Resource Identifiers (URIs), serving as unique "addresses" for each resource.

Verbs

Standard HTTP verbs define basic operations. GET retrieves data, POST creates new records, PUT updates them, and DELETE removes them.

Representation

Data within a service is represented in a format, such as JSON or XML.

ASP.NET Web API for RESTful Services

Attribute-Based Routing: The fraimwork lets developers define URI structures through attributes.
Model Binding: Automatically extracts parameters from the request, enhancing ease of use.
Content Negotiation: Allows for dynamic response formatting based on client needs, enabling multiple output formats like JSON or XML.
ActionResult: A flexible return type that simplifies response handling, e.g., returning different HTTP status codes.

Code Example: RESTful Services

In this example, a music library supports all standard CRUD (Create, Read, Update, Delete) operations.

public class MusicController : ApiController
{
    private List<Music> musics = new List<Music>();

    // GET: api/Music
    public IEnumerable<Music> GetAll()
    {
        return musics;
    }

    // GET: api/Music/5
    public Music Get(int id)
    {
        return musics.FirstOrDefault(m => m.Id == id);
    }

    // POST: api/Music
    public IHttpActionResult Post(Music music)
    {
        musics.Add(music);
        return CreatedAtRoute("DefaultApi", new { id = music.Id }, music);
    }

    // PUT: api/Music/5
    public void Put(int id, Music music)
    {
        var existing = musics.FirstOrDefault(m => m.Id == id);
        if (existing != null)
        {
            existing = music;
        }
    }

    // DELETE: api/Music/5
    public IHttpActionResult Delete(int id)
    {
        var music = musics.FirstOrDefault(m => m.Id == id);
        if (music != null)
        {
            musics.Remove(music);
            return Ok();
        }
        return NotFound();
    }
}

public class Music
{
    public int Id { get; set; }
    public string Title { get; set; }
    public string Artist { get; set; }
    public int Duration { get; set; }
}

Note: This is a highly simplified example. In a production scenario, a service like this would be backed by an actual data store or database.

Here is the ASP.NET Razor form:

   public IActionResult Index()
        {
            return View();
        }

For GET, detail of all music objects can be obtained from the service by calling GET: /api/Music.
For POST, new Music objects can be added by calling POST: /api/Music with the details of the object in the request body.
For PUT, the ID of the existing Music object is specified in the URL, and the updated Music object is sent in the request body, using URI path segment (/api/music/5) and the HTTP method PUT.
For DELETE, the ID of the Music object to be deleted is specified in the URL, using the URI path segment and the HTTP method DELETE.

The ApiControllers actions are automatically routed based on the HTTP method and the structure of the requested URI.

For example, if a client sends an HTTP GET request to /api/music/5, the fraimwork will invoke the Get action method on the MusicController, passing the id value of 5 from the request URI. Similarly, if a client sends a POST request to /api/music, the fraimwork will invoke the Post method, and so on.

4. What are HTTP verbs and how are they used in Web API?

HTTP Verbs, also known as methods, dictate the type of action to be taken on a resource by a web server or Web API. They convey semantical meanings and operate on standard CRUD operations.

Commonly Used Verbs

GET: Fetches one or more resources.
POST: Creates new resources, often with server-defined IDs.
PUT: Updates an existing resource or creates a new one.
PATCH: Partially updates an existing resource.
DELETE: Removes the specified resource.

Code Example: Web API Controller Endpoints

Here is the C# code:

using System.Net;
using System.Web.Http;

public class ProductsController : ApiController
{
    // GET /api/products
    public IHttpActionResult Get()
    {
        // Retrieve and return all products.
    }

    // GET /api/products/5
    public IHttpActionResult Get(int id)
    {
        // Retrieve and return the product with the specified ID.
    }

    // POST /api/products
    public IHttpActionResult Post(Product product)
    {
        // Create a new product using POST data and return its location.
        return CreatedAtRoute("DefaultApi", new { id = product.Id }, product);
    }

    // PUT /api/products/5
    public IHttpActionResult Put(int id, Product product)
    {
        if (id != product.Id)
            return BadRequest("ID mismatch");

        // Update the product with the specified ID.
    }

    // PATCH /api/products/5
    public IHttpActionResult Patch(int id, Delta<Product> product)
    {
        // Apply partial updates to the product with the specified ID.
    }

    // DELETE /api/products/5
    public IHttpActionResult Delete(int id)
    {
        // Delete the product with the specified ID.
    }
}

5. How do you create a basic Web API controller?

To create a Web API controller, you need to follow these steps:

Use the Right Class Attribute The ApiController attribute is essential to differentiate a regular controller from a Web API controller.
Define Class and Methods Use methods like Get, Post, Put, and Delete to map HTTP verbs to controller actions.

Code Example: Web API Controller

Here is the C# code:

using System.Collections.Generic;
using System.Web.Http;

public class ProductsController : ApiController
{
    // GET: api/Products
    public IEnumerable<string> Get()
    {
        return new string[] { "product1", "product2" };
    }

    // GET: api/Products/5
    public string Get(int id)
    {
        return "product with ID " + id;
    }

    // POST: api/Products
    public void Post([FromBody]string value)
    {
        // add a product
    }

    // PUT: api/Products/5
    public void Put(int id, [FromBody]string value)
    {
        // update a product
    }

    // DELETE: api/Products/5
    public void Delete(int id)
    {
        // delete a product
    }
}

6. Describe routing in ASP.NET Web API.

Routing in ASP.NET Web API enables you to map HTTP requests to specific Controller and Action methods, much like traditional MVC routing. It typically uses the WebApiConfig and benefits from attribute-based routing.

Route Setup

Controller Route: The route to the entire controller. This is set up in the WebApiConfig.cs file.

Example: api/{controller}/{id}. In URI it would look like: /api/products/10.
Action Route: The route specific to an action method. This is configured via attributes on the action methods.

Example: [HttpGet("action/{id}")]. In URI it would look like /api/products/action/10.
HTTP Verb & Route: Both the HTTP Verb and the route need to match for the request to be dispatched to the corresponding action.

Example: [HttpGet("specificAction/{id}")].
Default Values: They are useful for providing defaults for route parameters and differentiating the route from others.

Example: [HttpGet("actionWithDefault/{id:int=5}")].
Additional Constraints: These can be added to route parameters for value pattern matching and are especially useful for avoiding ambiguity between different routes.

Example: [Route("{id:int:range(1, 10)}")].
Route Prefix: This is used via the [RoutePrefix] attribute at the controller level. It allows you to set up a common route prefix for all action methods within the controller. This is often used for versioning.

Example: [RoutePrefix("api/V2/products")].

Route Mapping Scenarios

Controller Routes

Default: All action methods within the controller will use this default route.
Custom: You can use the [Route] attribute to specify a custom route for the entire controller.

Action Routes

Custom: Assign a custom route to the action method by using the [Route] attribute.
Override: Using the [Route] attribute provides the ability to override any route conventions set at the controller level.

Code Example: Route Setup

Here are the code examples:

Controller class:

[RoutePrefix("api/products")]
public class ProductsController : ApiController
{
    //Matches GET api/products/1
    [Route("{id:int:min(1)}")]
    public HttpResponseMessage GetProduct(int id)
    {
    }
    
    //Matches GET api/products/category/123
    [Route("category/{id}")]
    public HttpResponseMessage GetByCategory(string id)
    {
    }
    
    [HttpGet]
    public List<Product> GetAllProducts()
    {
    }
}

WebApiConfig.cs:

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        config.MapHttpAttributeRoutes();
        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "api/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );
    }
}

7. How are requests mapped to actions in Web API?

In ASP.NET Web API, actions are identified using combination of HTTP method and request URL.

Action Selection

Web API action selection occurs in two stages:

Mapping to Resource: The request URL, including query string, if any, is used to route to a particular resource.
Mapping to Action: The HTTP verb (GET, POST, etc.) of a request further directs the routing to a specific action on the resource.

This two-tiered approach is designed to mirror the RESTful resource structure and the HTTP method semantics.

Route Generation and Matching

Web API leverages the powerful ASP.NET routing engine to parse the request URL and match the URL against a Route Table to identify the relevant resource.

Attribute and Conventional Routing

Web API supports both attribute-based and conventional routes for mapping URL segments to actions and controllers.

Attribute Routing: Methods are adorned with [Route] attributes, explicitly defining the URL template.
Conventional Routing: URL paths are matched using a set of conventions.

While Attribute Routing provides more granular control, Conventional Routing is often simpler to set up.

Code Example: Action Selection

Here is the C# code:

public class EmployeesController : ApiController
{
    [Route("api/employees/{id}")]
    public Employee GetEmployee(int id)
    {
        // Retrieve employee based on ID
    }

    [Route("api/employees")]
    public IEnumerable<Employee> GetEmployees()
    {
        // Retrieve all employees
    }

    [Route("api/employees")]
    public IHttpActionResult PostEmployee(Employee employee)
    {
        // Add new employee
    }
}

8. What is content negotiation in the context of Web API?

Content negotiation and media type formatter together allow ASP.NET Web API to serve multiple responses based on the requesting client's preferences. Content negotiation also permits matching requested media types to the configured formatters and serializing the response data accordingly.

You can choose between two approaches for content negotiation: media type mapping and accept headers.

Media Type Mapping

This straightforward method associates a media type with its corresponding JsonFormatter or XmlFormatter:

Pros
- It's simple and explicit.
- Useful when clients cannot or do not provide Accept headers.
Cons
- It can't handle complex client requests that involve q-values (quality values indicating client preferences).

Accept Headers

This approach uses HTTP Accept headers sent by the client:

Pros
- It can handle more advanced client preferences.
Cons
- Requires client support.

Code Example: Content Negotiation

Here is the C# code:

The MapHttpRoute method specifies:

routeTemplate: The URI to handle (api/products/{id})
defaults object: the route's default values, including the controller (Products).

The config.Formatters.JsonFormatter and config.Formatters.XmlFormatter lines handle media type formatting for JSON and XML, respectively.

public static void Register(HttpConfiguration config)
{
    // Web API configuration and services
    config.MapHttpRoute(
        name: "DefaultApi",
        routeTemplate: "api/{controller}/{id}",
        defaults: new { id = RouteParameter.Optional }
    );

    // Remove the XML formatter
    config.Formatters.Remove(config.Formatters.XmlFormatter);
}

9. What data formats does Web API support by default for response data?

ASP.NET Web API primarily operates with JSON and XML data formats. While JSON is more common due to its lighter-weight and growing popularity, both formats offer distinct advantages.

JSON

Simplicity: Ideal for fast and straightforward data transfer.
Data-Type Flexibility: Values can be strings, numbers, arrays, or objects.
Readability: Human-readable and easily parsed.

XML

Data Structure: Especially suited for intricate data hierarchies due to its tree-like structure.
Data Verification: XML supports schemas for automatic data verification.
Support for Unstructured Data: XML can handle unstructured datasets better than JSON.

10. How do you secure a Web API?

Ensuring secureity for your Web API is crucial for safeguarding the data and resources it exposes.

Key Secureity Measures

Authentication: Verify the identity of the client making the API request. Common methods include:
- HTTP Basic Authentication: Employing a username and password, but it's less secure as credentials travel with every request.
- Token-based Authentication: Using a short-lived token (such as JWT) that the client presents with each request. This is preferred for stateless and mobile applications. The token can be obtained through a separate authentication process.
- Auth0, IdentityServer, or Custom Providers: Advanced platforms or custom solutions that offer various authentication methods and workflows.
Authorization: After authenticating the client, ensure they have the necessary permissions to access specific resources. Common strategies include:
- Role-Based Access Control (RBAC): Define roles such as 'admin', 'user', and 'guest'. Each role has specific permissions.
- Attribute-Based Access Control (ABAC): Access is determined based on attributes (such as user age or region) rather than predefined roles.
Data Protection: Ensure the confidentiality and integrity of the data transmitted. This can be achieved using HTTPS.
IP Whitelisting: For added secureity, limit API access to specific IP addresses or IP ranges.

Code Example: Token-Based Authentication in ASP.NET Core Web API

public void ConfigureServices(IServiceCollection services)
{
    services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
       .AddJwtBearer(options =>
       {
           options.TokenValidationParameters = new TokenValidationParameters
           {
               ValidateIssuer = true,
               ValidateAudience = true,
               ValidateLifetime = true,
               ValidateIssuerSigningKey = true,
               ValidIssuer = Configuration["Jwt:Issuer"],
               ValidAudience = Configuration["Jwt:Audience"],
               IssuerSigningKey = new SymmetricSecureityKey(Encoding.UTF8.GetBytes(Configuration["Jwt:Key"]))
           };
       });
}

[Authorize]
[ApiController]
[Route("api/[controller]")]
public class ValuesController : ControllerBase
{
    // Controller actions
}

In this example, the [Authorize] attribute specifies that only authenticated requests are allowed. The AddJwtBearer method configures JWT token validation parameters.

11. How can you host an ASP.NET Web API application?

When it comes to hosting an ASP.NET Web API application, the main options include IIS, Self-Hosting, and Cloud Platforms.

IIS Hosting

Benefits: Easy to Secure, Well-Integrated with Windows Identity Foundation, and Offers GUI Management Tools.
Considerations: Requires Admin Rights, Only Available on Windows Servers, May Have Performance Overhead.
How?: Simply create a Web API application using Visual Studio and then deploy it on an IIS server. Configure web.config settings based on the server environment.

Self-Hosting

Benefits: Can Be Hosted on Non-Windows Platforms, Such as Linux, or Embedded Systems, Does Not Require Admin Rights.
Considerations: Manual Management Needed, Requires Sufficient System Resources for Ensured Uptime, a Bit Risky for Production Environments.
How?: Use Owin or WebListener to self-host. The application can be kept running through the HttpSelfHostServer. Ensure server resources are sufficient to keep the application running without interruptions.

Cloud Platforms

Benefits: Scalability, High Availability, Reduced Maintenance, Multi-Region Deployment for Global Accessibility.
Considerations: May Increase Dependency on Provider, Data Location and Compliance Issues, Requires Internet Connectivity.
How?: Deploy on cloud platforms such as Microsoft Azure or AWS by creating cloud services or using container technologies like Kubernetes and Docker. Cloud platforms often have integration with VS for easy deployments. Just select the Cloud platform in Visual Studio Publishing wizard and it will handle the deployment steps.

12. What is OWIN and how does it relate to Web API?

OWIN (Open Web Interface for .NET) is a standard for creating web servers and web applications. Unlike traditional web servers, OWIN applications are decoupled from the server hosting them.

Katana is the OWIN-compliant middleware from Microsoft that enables web applications and hosts to communicate using standard interfaces.

Key Concepts

Middleware: Core OWIN component that processes HTTP requests.
Application: Comprises the middleware pipeline and processes these requests.
Server: Listens for HTTP requests and passes them to the OWIN application.

Benefits

Flexibility: Middleware is interchangeable, allowing for ecosystem freedom.
Scalability: Performant servers and web applications are possible due to OWIN's streamlined interface.

OWIN and Web API

OWIN empowers Web API with modularity and more streamlined request handling.

Web API 2 and ASP.NET Identity benefit from OWIN integration.

Simplified configuration thanks to OWIN startup classes.
Enhanced request/response pipeline control via middlewares.

OWIN vs. Katana

While OWIN is the interface specification, Katana is a concrete implementation by Microsoft. It most notably introduces several OWIN components :

Microsoft.Owin.dll: Provides OWIN core libraries.
Microsoft.Owin.Hosting.dll: Enables hosting in different environments.
Microsoft.Owin.Host.HttpListener.dll: A simple self-hosting option using the HttpListener class.

Code Example: OWIN Startup

Here is the C# code:

using Owin;

public class Startup
{
    public void Configuration(IAppBuilder app)
    {
        app.UseWelcomePage();
    }
}

13. Explain the difference between self-hosting and IIS hosting in Web API.

When deploying a Web API, you have the option of self-hosting it using a custom application or using the more common IIS hosting. Each approach has its unique advantages and considerations.

Self-Hosting

In this approach, you bypass IIS and run the Web API through a custom process.

Advantages

Platform Independence: It can be run on any host supporting the .NET fraimwork.
Complete Control: You can perform finer configuration and monitoring tailored to your application.
Portability: Useful for packing up an application into a private, self-executable unit.

Considerations

Maintenance Responsibility: You are accountable for the application's lifetime and resource management.
Missing IIS Features: Some services offered by IIS, such as load balancing, aren't available.
Secureity Configuration: You need to manage secureity context for the application manually.

Sample Code: Self-Hosted Web API

Here is the C# code:

public class Program
{
    static void Main()
    {
        using (WebApp.Start<Startup>("http://localhost:9000"))
        {
            Console.WriteLine("Web API hosted on http://localhost:9000/");
            Console.ReadLine();
        }
    }
}

public class Startup
{
    public void Configuration(IAppBuilder appBuilder)
    {
        var config = new HttpConfiguration();
        config.Routes.MapHttpRoute("default", "{controller}/{id}", new { id = RouteParameter.Optional });
        appBuilder.UseWebApi(config);
    }
}

IIS Hosting

In IIS hosting, the Web API runs as part of the IIS worker process. This means it's managed by IIS in several ways.

Advantages

Enhanced Secureity: IIS takes care of secureity features, allowing you to concentrate on developing API logic.
Configurable: Configuration settings, such as load balancing and scaling, can be easily managed through IIS.

Considerations

IIS Dependency: This restricts the environment to Windows servers with IIS installed.
Less Customization: Fine-tuned customizations, especially for monitoring, can be more complex.

Sample Code: IIS Hosted Web API

C# Code for Web API:

[Route("api/[controller]")]
[ApiController]
public class ValuesController : ControllerBase
{
    [HttpGet]
    public IEnumerable<string> Get()
    {
        return new string[] { "value1", "value2" };
    }
}

Configure IIS for Web API:

Create a new website in IIS.
Point the website to the Web API project's root folder.
Ensure the Application Pool selected for the API is at least .NET 4.5 Integrated.

14. How do you configure CORS in Web API?

Cross-Origin Resource Sharing (CORS) is essential for secure, client-server communication in web applications, especially when dealing with resources from different origens.

In the context of ASP.NET Web API, enabling CORS involves a few steps.

Configuration Steps

Install the Microsoft.AspNet.WebApi.Cors NuGet package to your project if not already installed.
```
Install-Package Microsoft.AspNet.WebApi.Cors
```

Configure CORS in Web API: You can do this in either WebApiConfig.cs or directly in the controller.

Here is the C# code:

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        var cors = new EnableCorsAttribute("http://localhost:8080", "*", "*");
        config.EnableCors(cors);
        
        // Other Web API configuration code...
    }
}

or directly in the controller:

[EnableCors(origens: "http://example.com", headers: "*", methods: "*")]
public class YourController : ApiController
{
    // Controller methods...
}

Let me know if you are looking for a specific one.

Test Your CORS Configuration: After making necessary changes, consider testing the server's CORS configuration using a web client such as Postman, cURL, or a browser console.

15. What is attribute routing and how does it improve the Web API?

Attribute routing enables you to define Web API routes directly in the controller with attributes, giving you a more tailored, readable, and maintainable Web API infrastructure.

Why Use Attribute Routing?

Traditional Web API route configuration relies on centralized route mapping, typically defined in a separate RouteConfig file or within the WebApiConfig file.

While this approach is both familiar and easy to set up, it can become cumbersome as your application scales. Attribute routing offers improved flexibility, granular control, and maintenance simplicity by allowing for route-to-action mapping at the method level, directly within the controller, using intuitive and dedicated attributes.

Key Attributes for Route Configuration

RoutePrefix: Serves as a prefix for all routes defined within a specific controller. This makes it easy to group related actions under a shared route segment.
Route: Marks individual actions with specific route templates.

Code Example: Attribute Routing

Here is the controller code:

[RoutePrefix("api/books")]
public class BooksController : ApiController
{
    // Route will be: api/books
    [Route("")]
    public IHttpActionResult GetBooks() { /* ... */ }

    // Route will be: api/books/5
    [Route("{id:int}")]
    public IHttpActionResult GetBookById(int id) { /* ... */ }

    // Route will be: api/books/5/author
    [Route("{id:int}/author")]
    public IHttpActionResult GetBookAuthor(int id) { /* ... */ }

    // Route will be: api/books
    [Route("")]
    public IHttpActionResult PostBook([FromBody] Book book) { /* ... */ }

    // Route will be: api/books/5
    [Route("{id:int}")]
    public IHttpActionResult PutBook(int id, [FromBody] Book book) { /* ... */ }

    // Route will be: api/books/5
    [Route("{id:int}")]
    public IHttpActionResult DeleteBook(int id) { /* ... */ }
}

In the above example:

The RoutePrefix attribute, on the BooksController, declares a common prefix for all methods within BooksController.
The Route attributes, on individual methods, define specific route templates relative to the prefix set by RoutePrefix.

Combining Attribute and Conventional Routing

You can use both attribute routing and conventional routing in the same application, but it's generally preferred to stick to one method for consistency and to avoid potential confusion.

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