返回 MediatR 管道行为错误的响应

Question

我是 MediatR 的新手，尝试使用管道行为进行请求验证，如果发生任何错误，我遇到的所有示例都会抛出 ValidationException 。
下面的代码是验证管道的示例：

public class ValidationPipeline<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
where TRequest : IRequest<TResponse>
{
    private readonly IEnumerable<IValidator> _validators;

    public ValidationPipeline(IEnumerable<IValidator<TRequest>> validators)
    {
        _validators = validators;
    }

    public Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate<TResponse> next)
    {
        var context = new ValidationContext<TRequest>(request);
        var validationFailures = _validators
            .Select(validator => validator.Validate(context))
            .SelectMany(validationResult => validationResult.Errors)
            .Where(validationFailure => validationFailure != null)
            .ToList();

        if (validationFailures.Any())
        {
            throw new FluentValidation.ValidationException(validationFailures);
        }
        
        return next();
    }
}

这个方法工作正常，但我想返回带有验证错误的响应（不抛出异常），所以我尝试了这个：

public class ValidationBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, BaseResponse<TResponse>>
    where TRequest : IRequest<BaseResponse<TResponse>>
{
    private readonly IEnumerable<IValidator> _validators;

    public ValidationBehavior(IEnumerable<IValidator<TRequest>> validators)
    {
        _validators = validators;
    }

    public Task<BaseResponse<TResponse>> Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate<BaseResponse<TResponse>> next)
    {
        var context = new ValidationContext<TRequest>(request);
        var validationFailures = _validators
            .Select(validator => validator.Validate(context))
            .SelectMany(validationResult => validationResult.Errors)
            .Where(validationFailure => validationFailure != null)
            .ToList();

        if (validationFailures.Any())
        {
            return Task.FromResult(new BaseResponse<TResponse>
            {
                Code = 400,
                Message = "Validation error",
                Error = validationFailures.Select(err => err.ErrorMessage)
            });
        }
        else
        {
            return next();
        }
    }

但现在验证管道代码不执行，
而是执行到常规处理程序（例如：注册用户处理程序）。

我的回应（在所有处理程序中使用）：

public class BaseResponse<TResponse>
{
    public int Code { get; set; }
    public string Message { get; set; }
    public TResponse Result { get; set; }
    public object Error { get; set; }
    public string TraceIdentifier { get; set; }
}

向 DI 注册行为，如下所示：

services.AddTransient(typeof(IPipelineBehavior<,>), typeof(ValidationBehavior<,>));

任何帮助将不胜感激。

Answer 1

我用了下一个方法。首先，我使用Adrdalis.Result或通过 nuget Ardalist.Result我发现它非常有用。管道代码：

public class FluentValidationPipelineBehaviour<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
where TRequest : IRequest<TResponse>
{
    private readonly IEnumerable<IValidator<TRequest>> _validators;

    public FluentValidationPipelineBehaviour(IEnumerable<IValidator<TRequest>> validators)
    {
        _validators = validators;
    }
    public async Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate<TResponse> next)
    {
        var requestType = request.GetType();
        if (requestType != null)
        {
            var attribute = requestType.GetCustomAttribute<FluentValidationAttribute>();
            if (attribute != null && attribute.IsEnabled)
            {
                var context = new ValidationContext<TRequest>(request);
                var validationResults = await Task.WhenAll(
                    _validators.Select(v =>
                        v.ValidateAsync(context, cancellationToken)));

                var failures = validationResults
                    .Where(r => r.Errors.Any())
                    .SelectMany(r => r.Errors)
                    .ToList();
            
                if (failures.Any())
                {
                    if (attribute.ThrowExceptionOnError)
                    {
                        throw new ValidationException(failures);
                    }
                    return GetValidatableResult(failures.AsErrors());
                }
            }
        }
        return await next();
    }

    private static TResponse GetValidatableResult(List<ValidationError> validationErrors)
    {
#pragma warning disable CS8603
#pragma warning disable CS8602
#pragma warning disable CS8600
        return (TResponse)(typeof(Result<>).MakeGenericType(typeof(TResponse).GetGenericArguments())
            .GetMethod("Invalid").Invoke(null, new object?[] { validationErrors }));
#pragma warning restore CS8600
#pragma warning restore CS8602
#pragma warning restore CS8603
    }
}

我正在使用 FluentValidationAttribute 来配置 FluentValidation 行为

[AttributeUsage(AttributeTargets.Class, Inherited = false, AllowMultiple = false)]
public class FluentValidationAttribute : Attribute
{
    public bool IsEnabled { get; set; } = true;
    public bool ThrowExceptionOnError { get; set; } = false;
}

在命令/查询等上使用它；