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ASP.NET API With Controllers

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ASP.NET Controller APIs

In ASP.NET Core, controller-based APIs organize related endpoints into classes that inherit from ControllerBase. This class provides essential HTTP functionality including status code responses, model binding, and request handling.

public class ProductsController : ControllerBase
{
    [HttpGet]
    public ActionResult<IEnumerable<Product>> GetAll() => _products;
    
    [HttpGet("{id}")]
    public ActionResult<Product> GetById(int id) => _products.FirstOrDefault(p => p.Id == id);
}

[ApiController] in ASP.NET

In ASP.NET Core, the [ApiController] attribute enhances controller classes with API-specific behaviors that reduce boilerplate code. This attribute automatically performs model validation, infers parameter binding sources, and returns standardized problem details for errors without requiring manual implementation.

[ApiController]
[Route("api/products")]
public class ProductsController : ControllerBase
{
    // Model validation happens automatically
    // Parameter binding sources are inferred
}

[Route] in ASP.NET

In ASP.NET Core, the [Route] attribute defines the URL patterns for controller endpoints with the route template passed as a string parameter.

[Route("api/[controller]")]     // Resolves to "api/products" 
public class ProductsController : ControllerBase
{
    [HttpGet]
    public ActionResult<Product> Get() => _products;
}

ASP.NET HTTP Verbs

In ASP.NET Core, HTTP verb attributes ([HttpGet], [HttpPost], [HttpPut], [HttpDelete]) map controller action methods to specific HTTP operations:

public class ProductsController : ControllerBase
{
    [HttpGet]                       // Handles GET requests
    public ActionResult<Product[]> GetAll() => _products;
    
    [HttpPost]                      // Handles POST requests
    public ActionResult<Product> Create(Product product) => CreatedAtAction(nameof(GetById), new { id = product.Id }, product);
    
    [HttpPut("{id}")]               // Handles PUT requests
    public IActionResult Update(int id, Product product) => NoContent();
    
    [HttpDelete("{id}")]            // Handles DELETE requests
    public IActionResult Delete(int id) => NoContent();
}

Route Parameters

In ASP.NET Core, route parameters capture dynamic values from URLs using curly brace syntax {id} in route patterns and corresponding method parameters.

[HttpGet("{id}")]  // Captures dynamic value from URL
public ActionResult<Product> GetById(int id)  // Parameter name matches route parameter
{
    var product = _products.FirstOrDefault(p => p.Id == id);
    return product == null ? NotFound() : product;
}

ActionResult in ASP.NET

In ASP.NET Core, ActionResult<T> provides flexibility to return either data (200 OK) or status code responses (404 Not Found, 400 Bad Request) from controller actions.

public ActionResult<Product> GetById(int id)
{
    var product = _products.FirstOrDefault(p => p.Id == id);
    
    if (product == null)
        return NotFound();     // Returns 404 status code
    
    return product;            // Returns 200 OK with product data
}

ASP.NET Core Model Binding

In ASP.NET Core, model binding automatically maps request data to action method parameters with optional source binding attributes ([FromQuery], [FromBody], [FromRoute]).

// Automatic binding based on parameter names
[HttpGet("{id}")]
public ActionResult<Product> GetById(int id)  // id from route
{
    return _products.FirstOrDefault(p => p.Id == id);
}


// Explicit binding with source attributes
[HttpGet("search")]
public ActionResult<IEnumerable<Product>> Search(
    [FromQuery] string name,        // From query string
    [FromQuery] decimal? maxPrice,  // From query string
    [FromRoute] string category)    // From route
{
    return _products.Where(p => p.Name.Contains(name) && p.Price <= maxPrice);
}

ASP.NET Core Validation

In ASP.NET Core, data annotations like [Required] and [StringLength] enable declarative validation that is automatically enforced by the framework.

public class Product
{
    public int Id { get; set; }
    
    [Required]
    [StringLength(100, MinimumLength = 3)]
    public string Name { get; set; } = string.Empty;
    
}

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