FluentValidation errors to Logger - asp.net-core

Question

I'm registering my FluentValidation validators as follows:
services.AddFluentValidation(fv => fv.RegisterValidatorsFromAssemblyContaining<CustomRequestValidator>());
How can I get a handle of any validation errors to log them via my logging implementation, e.g. Serilog?

Answer 1

For users stumbling into this problem (like me) I'd like to provide the solution I found.
The actual problem is that ASP.NET Core, and APIs in particular, make Model State errors automatically trigger a 400 error response, which doesn't log the validation errors.
Below that same documentation they include instructions on how to enable automatic logging for that feature which I believe should be the correct solution to this problem.

Answer 2

To jump onto what #mdarefull said, I did the following:
public void ConfigureServices(IServiceCollection services)
{
// Possible other service configurations
services.AddMvc()
.ConfigureApiBehaviorOptions(options =>
{
options.InvalidModelStateResponseFactory = context =>
{
if (!context.ModelState.IsValid)
{
LogAutomaticBadRequest(context);
}
return new BadRequestObjectResult(context.ModelState);
};
});
// Possible other service configurations
}
The LogAutomaticBadRequest method is as follows:
private static void LogAutomaticBadRequest(ActionContext context)
{
// Setup logger from DI - as explained in https://github.com/dotnet/AspNetCore.Docs/issues/12157
var loggerFactory = context.HttpContext.RequestServices.GetRequiredService<ILoggerFactory>();
var logger = loggerFactory.CreateLogger(context.ActionDescriptor.DisplayName);
// Get error messages
var errorMessages = string.Join(" | ", context.ModelState.Values
.SelectMany(x => x.Errors)
.Select(x => x.ErrorMessage));
var request = context.HttpContext.Request;
// Use whatever logging information you want
logger.LogError("Automatic Bad Request occurred." +
$"{System.Environment.NewLine}Error(s): {errorMessages}" +
$"{System.Environment.NewLine}|{request.Method}| Full URL: {request.Path}{request.QueryString}");
}