Пример реализации бэкенда на C# — 3.1. Простой API-контроллер

// Controllers/ProductsController.cs
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using YourProjectName.Data;
using YourProjectName.Models;

[ApiController]
[Route("api/[controller]")]
public class ProductsController : ControllerBase
{
    private readonly AppDbContext _context;

    public ProductsController(AppDbContext context)
    {
        _context = context;
    }

    [HttpGet("{id}")]
    public async Task<ActionResult<Product>> GetProduct(int id)
    {
        var product = await _context.Products.FindAsync(id);
        if (product == null)
            return NotFound();

        return product;
    }
}