will go over how the.NET 9 Core Minimal API Controller APIs differ from one another. Introduced in.NET 6.0, the Minimal API is a lightweight and quick API development that is improved in.NET 9. Additionally, it works well with microservices, tiny APIs, and lightweight services. The basic API lacks [HttpGet] and routing characteristics. All of the logics are defined in Program.cs, making it simpler. The controller-based API is structured, scalable, and based on the Model-View-Controller (MVC) design. It will work well for complicated and sizable applications. Different controller classes are used to structure logics.

Will see how to create and run both a minimal API and a Controller API. First, to create the minimal API, run the following command in the command line.

dotnet new web -n MinimalApiDemo
cd MinimalApiDemo

In the program.cs file mapping the URL and function, there are no controllers and attributes; simply added routed mappings.

Minimal API Example
var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

var products = new List<Product>
{
    new(1, "Laptop", 999.99m),
    new(2, "Phone", 499.99m)
};

app.MapGet("/products", () => products);

app.MapGet("/products/{id}", (int id) =>
    products.FirstOrDefault(p => p.Id == id) is Product product
        ? Results.Ok(product)
        : Results.NotFound());

app.MapPost("/products", (Product product) =>
{
    products.Add(product);
    return Results.Created($"/products/{product.Id}", product);
});

app.Run();

To check the output, visit 'https://localhost:5001/product/1'.

Controller API Example
To create an MVC controller-based AP,I run the below command.
dotnet new webapi -n ControllerApiDemo
cd ControllerApiDemo

Here we will have a simple product API example, with [HttpGet] routing example given below.
using Microsoft.AspNetCore.Mvc;

[ApiController]
[Route("api/[controller]")]
public class ProductsController : ControllerBase
{
    private static readonly List<Product> Products = new()
    {
        new Product { Id = 1, Name = "Laptop", Price = 1200 },
        new Product { Id = 2, Name = "Smartphone", Price = 800 }
    };

    [HttpGet]
    public ActionResult<IEnumerable<Product>> GetAll()
    {
        return Ok(Products);
    }

    [HttpGet("{id}")]
    public ActionResult<Product> GetById(int id)
    {
        var product = Products.FirstOrDefault(p => p.Id == id);
        if (product == null) return NotFound();
        return Ok(product);
    }
}

To check the output, visit 'https://localhost:5001/api/products'