Gists for Medium Article - BusinessValidationPipeline

BusinessValidationPipeline.cs

public class BusinessValidationPipeline<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
	where TResponse : class
	where TRequest : IValidateable
{
	private readonly IValidator<TRequest> _compositeValidator;
	private readonly ILogger<TRequest> _logger;
	private readonly ICurrentUser _currentUser;
	private readonly IActionContextAccessor _actionContextAccessor;

	public BusinessValidationPipeline(
		IValidator<TRequest> compositeValidator,
		ILogger<TRequest> logger,
		ICurrentUser currentUser,
		IActionContextAccessor actionContextAccessor)
	{
		_compositeValidator = compositeValidator;
		_logger = logger;
		_currentUser = currentUser;
		_actionContextAccessor = actionContextAccessor;
	}

	public async Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate<TResponse> next)
	{
		_logger.TraceBeforeValidatingMessage();

		var responseType = typeof(TResponse);

		if (responseType.Name.StartsWith(nameof(ValidateableResponse), StringComparison.Ordinal))
		{
			var result = await _compositeValidator.ValidateAsync(request, cancellationToken);

			if (!result.IsValid)
			{
				var errorsCollated = result.ToDictionary();

				_logger.TraceMessageValidationFailed(errorsCollated, _currentUser?.UserName ?? GeneralPurpose.AnonymousUser);

				// Add validation fail to ModelState to make it available there. Just in case it is needed.
				result.AddToModelState(_actionContextAccessor.ActionContext.ModelState, string.Empty);

				// Deal with type depending on whether it is the generic version of ValidateableResponse or not.
				var resultType = responseType.GetGenericArguments().FirstOrDefault();

				if (ReferenceEquals(resultType, null))
				{
					var nonGenericInvalidResponse =
						Activator.CreateInstance(
							responseType,
							errorsCollated
							) as TResponse;

					return nonGenericInvalidResponse;
				}

				var invalidResponseType = typeof(ValidateableResponse<>).MakeGenericType(resultType);

				var invalidResponse =
					Activator.CreateInstance(
						invalidResponseType,
						null,
						errorsCollated
						) as TResponse;

				return invalidResponse;
			}

			_logger.TraceMessageValidationPassed();

			return await next();
		}

		throw new Exception($"IValidateable implementation must be a {nameof(ValidateableResponse)}.");
	}
}