MediatR IPipelineBehavior<TRequest, TResponse> 错误为类型“TRequest”不能用作泛型类型或方法中的类型参数“TRequest”

Question

我正在使用MediatR在我的应用程序中进行请求-响应日志记录IPipelineBehavior<TRequest, TResponse>

代码示例：

internal sealed class AppLoggingBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
{
    private readonly ILogger<AppLoggingBehavior<TRequest, TResponse>> _logger;

    public AppLoggingBehavior(ILogger<AppLoggingBehavior<TRequest, TResponse>> logger)
    {
        _logger = logger;
    }

    public async Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate<TResponse> next)
    {
        string requestName = typeof(TRequest).Name;
        string unqiueId = Guid.NewGuid().ToString();
        string requestJson = JsonSerializer.Serialize(request);
        _logger.LogInformation($"Begin Request Id:{unqiueId}, request name:{requestName}, request json:{requestJson}");
        var timer = new Stopwatch();
        timer.Start();
        var response = await next();
        timer.Stop();
        _logger.LogInformation($"End Request Id:{unqiueId}, request name:{requestName}, total request time:{timer.ElapsedMilliseconds}ms");
        return response;
    }
}

但是升级到之后Nuget - v10.0.0我开始收到以下编译错误。

类型“TRequest”不能用作通用类型或方法“IPipelineBehavior<TRequest, TResponse>”中的类型参数“TRequest”。没有从“TRequest”到“MediatR.IRequest”的装箱转换或类型参数转换

我设法从官方仓库找到了移植指南MediatR。但找不到任何例子。

我还缺少其他东西吗，有人可以帮助我吗？

Answer 1

TRequest您还需要在抽象类中指定参数的类型。它必须至少与您尝试实现的接口中的参数一样具体。

internal sealed class AppLoggingBehavior<TRequest, TResponse>
    : IPipelineBehavior<TRequest, TResponse>
    where TRequest : MediatR.IRequest<TResponse> // <- this is the part you're missing
{
    // rest of your code...
}