使用 MediatR 执行 API 方法时，出现错误

Question

这是我第一次实现 Mediator，但现在调用 API 方法时出现以下错误：

错误

{"error":"Enumerator failed to MoveNextAsync."}

DI

services.AddMediatR(Assembly.GetExecutingAssembly());
services.AddTransient(typeof(IPipelineBehavior<,>), typeof(RequestValidationBehavior<,>));

基础 API

[ApiController]
[Route("api/[controller]")]
public abstract class ApiController : ControllerBase
{
    private IMediator _mediator;

    protected IMediator Mediator => _mediator ??= HttpContext.RequestServices.GetService<IMediator>();
}

API

[HttpGet]
[Route("client/{clientId}/template/list")]
public async Task<ActionResult<TemplateListDTO>> GetClientTemplateList(long clientId)
{
    return await Mediator.Send(new GetClientTemplateListQuery { ClientId = clientId });
}

我正在使用 DotNet 核心 3.1

Answer 1

这里描述了这个问题：

https://github.com/jbogard/MediatR/issues/317

啊。你不能用 vanilla 做泛型类型约束 MS.Extensions.DI。请参阅我的 PR 以解决此问题： https://github.com/aspnet/DependencyInjection/pull/635

执行以下操作：

services.AddScoped(typeof(IPipelineBehavior<CustomerAddRequest, CommandResponse>), typeof(CustomerAddBehavior<CustomerAddRequest, CommandResponse>));
services.AddScoped(typeof(IPipelineBehavior<BrandDeleteRequest, CommandResponse>), typeof(BrandDeleteBehavior<BrandDeleteRequest, CommandResponse>));
services.AddScoped(typeof(IPipelineBehavior<CustomerDeleteRequest, CommandResponse>), typeof(CustomerDeleteBehavior<CustomerDeleteRequest, CommandResponse>));

Answer 2

我发现了问题，不是 Mediator 的问题。管道发生异常，处理不正确，无法进入 next() 管道。