📌 Routing in Web API – Extended Guide with Real-World Examples

🔍 Overview

Routing is the heart of a Web API. It determines how incoming HTTP requests are mapped to the correct controller and action method. In a real application, proper routing helps organize endpoints, manage versions, and keep APIs intuitive.

📁 Real Project Folder Structure Example

Here’s how a typical ASP.NET Core Web API project with attribute routing and versioning might look:

MyApp.API/ ├── Controllers/ │ ├── v1/ │ │ └── ProductsController.cs │ ├── v2/ │ │ └── ProductsController.cs ├── Program.cs ├── Startup.cs (or Program.cs if using .NET 6+)

🔢 Versioned Routing

Versioning is useful when APIs evolve and newer clients require updated logic or data formats.

Example: Versioned Attribute Routing

namespace MyApp.API.Controllers.v1
{
    [ApiController]
    [Route("api/v1/[controller]")]
    public class ProductsController : ControllerBase
    {
        [HttpGet("{id}")]
        public IActionResult GetProductV1(int id)
        {
            return Ok($"Product {id} from V1");
        }
    }
}

namespace MyApp.API.Controllers.v2
{
    [ApiController]
    [Route("api/v2/[controller]")]
    public class ProductsController : ControllerBase
    {
        [HttpGet("{id}")]
        public IActionResult GetProductV2(int id)
        {
            return Ok($"Product {id} from V2 with extra fields");
        }
    }
}

Requests:

• GET /api/v1/products/10 → calls V1 controller
• GET /api/v2/products/10 → calls V2 controller

🧩 Route Constraints

Route constraints allow filtering routes based on data type or pattern.

Example: Adding Type Constraints

[HttpGet("{id:int}")]
public IActionResult GetById(int id)
{
    return Ok($"Integer ID: {id}");
}

[HttpGet("{name:alpha}")]
public IActionResult GetByName(string name)
{
    return Ok($"Name: {name}");
}

Requests:

• GET /api/products/123 → goes to GetById
• GET /api/products/iphone → goes to GetByName

Common Route Constraints

Constraint	Description	Example
int	Must be an integer	{id:int}
guid	Must be a GUID	{id:guid}
alpha	Only letters (A–Z)	{name:alpha}
length	Fixed string length	{code:length(5)}
min/max	Min/max numeric limits	{age:min(18)}

✅ Clean Route Design Best Practices

• Use nouns, not verbs: /api/products instead of /api/getproducts
• Use plural resource names: /api/users, /api/orders
• Use query parameters for filtering: /api/products?category=mobile&inStock=true
• Maintain route consistency across versions
• Prefer attribute routing over convention-based for clarity and control

📌 Summary

• Routing connects HTTP requests to action methods.
• Attribute routing is the modern, flexible approach.
• Versioning helps maintain backward compatibility.
• Constraints improve route matching precision.
• Clean route design improves maintainability and usability.