Asp.Net Core 实现查询时缓存修改后缓存过期

应用场景:

  在高速公路收费系统业务中， 我们的收费站列表信息被频繁各种查询，来自整个自治区的收费站都会查询站信息和其他业务，那么对于站信息查询来说就显得尤其重要， 因此我们设置过期时间为10分钟。 

 //去报using了 下面三个命名空间

using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Caching.Memory;
namespace Uixe.Blazor.Controllers
{
    [Authorize]
    [Route("api/[controller]")]
    [ApiController]
    public class PlazasController : ControllerBase
    {
        private readonly ApplicationDbContext _context;
        private readonly ILogger _logger;
        private readonly AppSettings _settings;
        //内存缓存IMemoryCache
        private readonly IMemoryCache _memoryCache;
        //在需要过期的缓存中 AddExpirationToken
        private  CancellationChangeToken _changeToken ;
        //用于修改时调用，以使得_changeToken关联的缓存过期
        private  CancellationTokenSource _cancellationToken;
        
        public PlazasController(ApplicationDbContext context, ILogger<PlazasController> logger, IOptions<AppSettings> option,IMemoryCache memoryCache)
        {
            _context = context;
            _logger = logger;
            _settings = option.Value;
            _memoryCache = memoryCache;
              //我们需要将CancellationTokenSource本身也缓存在缓存当中
            _cancellationToken = _memoryCache.GetOrCreate("cts" + nameof(PlazasController), a =>
            {
            //没当过期后重新创建CancellationTokenSource
                _cancellationToken = new CancellationTokenSource();
               //然后黄建 CancellationChangeToken并关联CancellationTokenSource
                _changeToken = new CancellationChangeToken(_cancellationToken.Token);
                //添加至当前缓存元素中以便当_cancellationToken.Canecel()被调用后，本身也能国企
                a.AddExpirationToken(_changeToken);
                return _cancellationToken;
            });
        }
  
        [HttpGet(), AllowAnonymous, Authorize(Roles = nameof(UserRole.Anonymous))]
        public async Task<ActionResult<List<Plaza>>> GetPlazas()
        {
            return await _memoryCache.GetOrCreateAsync("_plaza_GetPlazas",  a =>
            {
            //当完整信息或许返回时关联_changeToken
                a.AddExpirationToken(_changeToken);
                //设置如果不修改的过期时间 ， 因为可能会从数据库或者自动处理程序会修改后台数据。
                //或者其他程序修改了我们并不知道，所以待有过期时间
                a.AbsoluteExpirationRelativeToNow = TimeSpan.FromMinutes(10);
                return    _context.Plazas.ToListAsync();
            });
        }
        /// <summary>
        /// 根据指定的参数<paramref name="args"/>查询收费站信息
        /// </summary>
        /// <param name="args"></param>
        /// <returns></returns>
        [HttpPost("Query"), AllowAnonymous, Authorize(Roles = nameof(UserRole.Anonymous))]
        public async Task<ActionResult<ApiResultPage<List<Plaza>>>> QueryPlazas([FromBody] phc_PlazaQueryArgs args)
        {
          //这是个查询， 我们根据查询条件的对象序列化为json，然后取md5字符串作为key
            if (args == null) args = new phc_PlazaQueryArgs() {  currentPage=1, pageSize=10};
            var key = "_plaza_" + args.GetMd5Sum();
            return await _memoryCache.GetOrCreateAsync(key, async a =>
           {
               //同样设置过期时间
               a.AbsoluteExpirationRelativeToNow = TimeSpan.FromMinutes(10);
                //将_changeToken进行关联
               a.AddExpirationToken(_changeToken);
               var query = from p in _context.Plazas select p;
               if (!string.IsNullOrEmpty(args.plazaid))
               {
                   query = from q in query where q.Id.Contains(args.plazaid) || q.StationId.StartsWith(args.plazaid) select q;
               }
               if (!string.IsNullOrEmpty(args.ipaddress))
               {
                   query = from q in query where q.IPAddress.StartsWith(args.ipaddress) select q;
               }
               if (!string.IsNullOrEmpty(args.plazaname))
               {
                   query = from q in query where q.StationName.Contains(args.plazaname) select q;
               }
               int total  =await  query.CountAsync();
               var data = await query.Skip(args.pageSize * (args.currentPage - 1)).Take(args.pageSize).OrderBy(q=>q.Id).ToListAsync();
               return  new  ApiResultPage<List<Plaza>> (ApiCode.OK, "OK", new PageInfo() { Total = total, Current = args.currentPage, PageSize = args.pageSize, TotalPage = (total + args.pageSize - 1) / args.pageSize }, data);
           });
        }
   
        [HttpPut(), Authorize(Roles = nameof(UserRole.Administrator))]
        public async Task<IActionResult> PutPlaza(Plaza plaza)
        {
            _context.Entry(plaza).State = EntityState.Modified;
            try
            {
                await _context.SaveChangesAsync();
                //当我们修改并保存后，调用_cancellationToken，它会麦让与之关联所有缓存过期。
                _cancellationToken.Cancel();
            }
            catch (DbUpdateConcurrencyException)
            {
                if (!PlazaExists(plaza.Id))
                {
                    return NotFound();
                }
                else
                {
                    throw;
                }
            }
            return NoContent();
        }
     
        [HttpPost, Authorize(Roles = nameof(UserRole.Administrator))]
        public async Task<ActionResult<Plaza>> PostPlaza(Plaza plaza)
        {
            _context.Plazas.Add(plaza);
            await _context.SaveChangesAsync();
            //我们在添加数据时进行取消，
            _cancellationToken.Cancel();
            return CreatedAtAction("GetPlaza", plaza);
        }
    }
   }