ASP.NET Core Web API

This documentation provides a comprehensive guide to building Web APIs with ASP.NET Core. ASP.NET Core Web API is a framework for building HTTP services that can be accessed from a broad range of clients, including browsers and mobile devices.

Introduction to Web API

Web API allows you to build RESTful services and applications. It's built on the same ASP.NET Core infrastructure as MVC applications, providing a powerful and flexible way to expose data and functionality over HTTP.

Key features include:

• Support for various data formats (JSON, XML).
• Content negotiation.
• Routing and attribute routing.
• Model binding and validation.
• Dependency injection.
• Cross-Origin Resource Sharing (CORS).

Getting Started

To start building a Web API, you can create a new ASP.NET Core Web API project in Visual Studio or using the .NET CLI:

dotnet new webapi -o MyWebApiProject
cd MyWebApiProject

This will create a basic project structure with controllers ready to be implemented.

Controllers

Controllers are classes that handle incoming HTTP requests. They typically inherit from ControllerBase and contain action methods that map to specific HTTP verbs and routes.

using Microsoft.AspNetCore.Mvc;

[ApiController]
[Route("api/[controller]")]
public class ProductsController : ControllerBase
{
    [HttpGet]
    public ActionResult> Get()
    {
        return new string[] { "Product 1", "Product 2" };
    }

    [HttpGet("{id}")]
    public ActionResult Get(int id)
    {
        if (id <= 0) return BadRequest("Product ID must be positive.");
        return $"Product {id}";
    }
}

Routing

ASP.NET Core Web API supports two main routing approaches:

• Convention-based routing: Defined in the Program.cs (or Startup.cs) file.
• Attribute routing: Defined using attributes on controllers and action methods (e.g., [Route("api/[controller]")], [HttpGet("details/{id}")]). Attribute routing is generally preferred for Web APIs as it allows for more explicit and organized routing configurations.

Model Binding and Validation

Web API automatically binds incoming request data (query parameters, route parameters, request body) to controller action parameters. Validation can be performed using data annotation attributes.

public class CreateProductRequest
{
    [Required]
    [StringLength(100)]
    public string Name { get; set; }

    [Range(1, 1000)]
    public decimal Price { get; set; }
}

[HttpPost]
public IActionResult CreateProduct([FromBody] CreateProductRequest request)
{
    if (!ModelState.IsValid)
    {
        return BadRequest(ModelState);
    }
    // ... create product logic
    return Ok();
}

API Reference

Here's a quick reference for common HTTP status codes used in Web APIs:

Advanced Topics

• Authentication and Authorization
• Error Handling
• Dependency Injection
• Testing Web APIs
• Swagger/OpenAPI Integration