Net DB Web多級快取的實現

cache-control:max-age=5  #表示允許瀏覽器快取5秒(僅是允許，瀏覽器是否快取還看瀏覽器本身機制是否要遵循這套快取協定)

    public class HomeController : ControllerBase
    {
        [ResponseCache(Duration = 5)]//告訴瀏覽器可用快取5秒，Duration必須定義,不然請求會報錯
        [HttpGet("GetNowDateTime")]
        public string GetNowDateTime()
        {
            return DateTime.Now.ToString();
        }
    }

cache-control: public,max-age=5   #告訴瀏覽器進行快取
content-encoding: gzip
content-type: text/plain; charset=utf-8
date: Sun, 19 Mar 2023 07:17:50 GMT
server: Microsoft-IIS/10.0
vary: Accept-Encoding
x-powered-by: ASP.NET

cache-control: no-cache  #不從快取中取數

//app.UseCors(); //跨域,如果有
app.UseResponseCaching();//啟動伺服器快取,位置介於這兩中介軟體之間
app.MapControllers();

    public class HomeController : ControllerBase
    {
        [ResponseCache(Duration = 5)]//告訴瀏覽器可用快取5秒
        [HttpGet("GetNowDateTime")]
        public string GetNowDateTime()
        {
            return DateTime.Now.ToString();
        }
    }

a）無法解決惡意請求給伺服器帶來的壓力（Request Header帶上了cache-control: no-cache，不僅瀏覽器不讀快取，伺服器也不讀）
b）響應碼=200的Get或者Head的響應才會被快取
c）報文頭帶有Authorization、Set-Cookie等響應，不會快取

builder.Services.AddScoped<IDBHelper, SqlServerHelper>(); //db注入
builder.Services.AddMemoryCache();//記憶體快取

namespace DIDemo.Services
{
    public record Staff(int Id, string acc);
    public class SqlServerHelper : IDBHelper
    {
        List<Staff> _staff_list = new List<Staff>();
        public SqlServerHelper() {
            _staff_list.Add(new Staff(1,"tom"));
            _staff_list.Add(new Staff(2,"jerry"));
        }public Staff? GetStaff(int Id)
        {
            return this._staff_list.Find(x => x.Id == Id);
        }
    }
}

using DIDemo.Services;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Caching.Memory;

namespace DIDemo.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class HomeController : ControllerBase
    {
        private readonly IDBHelper _db;
        private readonly IMemoryCache _menCache;

        public HomeController(IDBHelper db, IMemoryCache menCache)
        {
            _db = db;
            _menCache = menCache;
        }

        [HttpGet("GetStaff")]
        public  ActionResult<Staff> GetStaff(int Id)
        {
            Console.WriteLine("begin");
            //1、從快取取資料   2、快取取不到，從資料庫取，新增快取
            var items =  _menCache.GetOrCreate<Staff>($"staff_{Id}",  (e) =>
            {
                Console.WriteLine("快取不存在,開始寫快取");
                e.AbsoluteExpirationRelativeToNow= TimeSpan.FromSeconds(15); //15s後過期
                e.SlidingExpiration = TimeSpan.FromSeconds(5); //5s滑動過期:5s記憶體取過快取,會重新開始計算5s
                return _db.GetStaff(Id);
            });
            if (items == null)
            {
                return NotFound($"員工ID={Id},不存在");
            }
            return items;
        }
    }
}