c# - 有没有办法跳过 MediatR 管道？

Question

我想缓存一些来自 CommandsHandlers 的响应。

我已经使用 IPipelineBehaviour 做到了这一点，但我的请求中只有 5% 确实必须有缓存，而其他 95% 必须跳过此管道。有没有办法做到这一点？

下面是我的代码。

谢谢!

     public class PipelineBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse> 
                                         where TRequest : IRequest<TResponse>, IProvideCacheKey
    {
        private readonly IMemoryCache _cache;
        public PipelineBehavior(IMemoryCache cache)
        {
            _cache = cache;
        }
        public async Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken, 
                                            RequestHandlerDelegate<TResponse> next)
        {
            // Check in cache if we already have what we're looking for
            var cacheKey = request.CacheKey;
            if (_cache.TryGetValue<TResponse>(cacheKey, out var cachedResponse))
            {
                return cachedResponse;
            }
            // If we don't, execute the rest of the pipeline, and add the result to the cache
            var response = await next();
            _cache.Set(cacheKey, response);
            return response;
        }
    }





     public class GetUserByEmailCommand : Command, IRequest<bool>, IProvideCacheKey
     {
        public string Email { get; set; }

        public string CacheKey =>  $"{GetType().Name}:{Email}";

        public override bool IsValid()
        {
            ValidationResult = new GetUserByEmailCommandValidation<GetUserByEmailCommand>().Validate(this);

            return ValidationResult.IsValid;
        }
    }



  public interface IProvideCacheKey
  {
        string CacheKey { get; }
  }

Answer 1

如果请求不可缓存以让管道继续，您可以将缓存行为包装在绕过的检查中。在您的情况下，您可能只需检查请求是否在 Handle 方法开始时实现您的接口(interface):

if (request is IProvideCacheKey)
{
   // perform cache behavior, return if cached and terminate the pipeline
}
// else continue the pipeline

有几个很好的例子更详细地说明了这一点:

https://lurumad.github.io/cross-cutting-concerns-in-asp-net-core-with-meaditr

https://anderly.com/2019/12/12/cross-cutting-concerns-with-mediatr-pipeline-behaviors/