MediatR PipelineBehavior 错误消息无法解析类型“FluentValidation.IValidator”1 的服务

Question

我有这个 ValidationBehavior

public sealed class ValidationBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
    where TRequest : IRequest<TResponse>
{
    private readonly IValidator<TRequest> _validator;

    public ValidationBehavior(IValidator<TRequest> validator)
    {
        _validator = validator;
    }

    public async Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate<TResponse> next)
    {
        _validator.ValidateAndThrow(request);
        return await next();
    }
}  

我有这个处理程序，

public class RemoveCurrencyHandler : IRequestHandler<RemoveCurrencyCommand, Unit>
{
    private readonly ApplicationContext _context;

    public RemoveCurrencyHandler(ApplicationContext context)
    {
        _context = context;
    }

    public async Task<Unit> Handle(RemoveCurrencyCommand request, CancellationToken cancellationToken)
    {
        var currency = await _context.Currency.FindAsync(request.Id);

        if (currency is null)
            throw new KeyNotFoundException();

        _context.Remove(currency);
        await _context.SaveChangesAsync();
        return Unit.Value;
    }
}  

每次我调用这个处理程序时，我都会收到错误消息无法解析类型“FluentValidation.IValidator”的服务，现在显然我知道原因是因为我缺少验证器，所以如果我添加此验证器，它就会消失，

public class RemoveCurrencyValidator : AbstractValidator<RemoveCurrencyCommand>
{

}  

但并非所有处理程序都需要 Validator，所以我不想添加空的 Validator > 类到处理程序那不需要它。还有其他选择吗？

Answer 1

MediatR 验证器 pipelines 使您能够在命令或查询处理程序执行之前和之后执行验证逻辑。
您可以更新 ValidationBehavior 类的构造函数以获取 IEnumerable。这样我们就可以随时解析该类（如果您不实现Validator，列表将为空）

// ValidationBehavior
public sealed class ValidationBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
    where TRequest : IRequest<TResponse>
{
    private readonly IEnumrable<IValidator<TRequest>> _validators;

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

    public async Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate<TResponse> next)
    {
        if(_validators.Any())
        {
            var validationResults = await Task.WhenAll(_validators.Select(v => v.ValidateAndThrow(request)));

            var failures = validationResults.SelectMany(r => r.Errors).Where(f => f != null).ToList();
            if (failures.Count != 0)
                throw new ValidationException(failures);
        }
        return await next();
    }
}