Web API Fundamentals

This document provides a comprehensive overview of the core concepts and principles behind building robust and scalable Web APIs using the .NET ecosystem.

Introduction

Web APIs (Application Programming Interfaces) are essential for modern software development, enabling communication between different applications and services over the web. They act as a contract, defining how requests can be made and what responses can be expected. .NET offers powerful tools and frameworks for creating and consuming Web APIs efficiently.

REST Principles

A RESTful API adheres to the Representational State Transfer (REST) architectural style. Key principles include:

Creating Web APIs in .NET

The primary framework for building Web APIs in .NET is ASP.NET Core. It provides a high-performance, cross-platform, and open-source framework for building modern, cloud-based, internet-connected applications.

Routing

Routing is the process of determining how an incoming request is mapped to a specific handler or controller action. ASP.NET Core uses a flexible routing system, often based on conventions or explicit route templates.

A common approach is attribute routing, where routes are defined directly on controller actions using attributes.

[ApiController]
[Route("api/[controller]")]
public class ProductsController : ControllerBase
{
    // ...
}

This sets up a base route like /api/products for the entire controller.

Controllers

Controllers are classes responsible for handling incoming HTTP requests and returning HTTP responses. In ASP.NET Core Web APIs, controller classes typically inherit from ControllerBase.

They are decorated with attributes like [ApiController], which enables several API-specific behaviors, such as automatic model validation and handling of HTTP 400 errors.

Action Methods

Action methods are public methods within a controller that handle specific HTTP requests for a given resource. The framework determines which action method to execute based on the HTTP verb (GET, POST, PUT, DELETE) and the route.

[HttpGet]
public IEnumerable<Product> Get()
{
    // Returns a list of products
    return _productRepository.GetAll();
}

[HttpGet("{id}")]
public ActionResult<Product> Get(int id)
{
    var product = _productRepository.GetById(id);
    if (product == null)
    {
        return NotFound(); // Returns HTTP 404
    }
    return Ok(product); // Returns HTTP 200 with product data
}

[HttpPost]
public IActionResult Post([FromBody] Product newProduct)
{
    if (!ModelState.IsValid)
    {
        return BadRequest(ModelState); // Returns HTTP 400
    }
    _productRepository.Add(newProduct);
    return CreatedAtAction(nameof(Get), new { id = newProduct.Id }, newProduct); // Returns HTTP 201
}

Data Formats (Serialization/Deserialization)

Web APIs typically exchange data in formats like JSON or XML. ASP.NET Core uses built-in support for JSON serialization via the System.Text.Json namespace (or Newtonsoft.Json for older projects).

The framework automatically serializes return values from action methods into the appropriate format (usually JSON by default) and deserializes incoming request bodies into C# objects.

HTTP Messages

Understanding HTTP is crucial for Web API development. Key components include:

Common HTTP status codes include:

Error Handling

Graceful error handling is vital for a good API experience. ASP.NET Core provides mechanisms for:

Note: Avoid returning detailed exception messages to clients in production environments for security reasons. Log detailed errors on the server.

Security Considerations

Securing your Web API is paramount. Common security measures include:

Tip: Explore ASP.NET Core's built-in identity management features and security middleware for robust protection.

This section covers the foundational aspects of building Web APIs. For advanced topics, refer to the specific documentation on data binding, dependency injection, testing, and deployment within ASP.NET Core.