ModelValidation.cs

using System;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;
using Microsoft.Extensions.Logging;
using Newtonsoft.Json;

namespace SchedulerApi.Filters
{
    /// <inheritdoc />
    /// <summary>
    /// This attribute takes care of returning 400 Bad Request when user input is not valid
    /// </summary>
    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method)]
    public class ValidateRequestBodyAttribute : TypeFilterAttribute
    {
        public ValidateRequestBodyAttribute() : base(typeof(ValidateRequestBodyAttributeImpl))
        {
        }
    }

    public class ValidateRequestBodyAttributeImpl : IAsyncActionFilter
    {
        private readonly ILoggerFactory _loggerFactory;

        public ValidateRequestBodyAttributeImpl(ILoggerFactory loggerFactory)
        {
            _loggerFactory = loggerFactory;
        }

        public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
        {
            if (!context.ModelState.IsValid)
            {
                BadRequestObjectResult result = new BadRequestObjectResult(context.ModelState);
                context.Result = result;

                ILogger logger = _loggerFactory.CreateLogger("ModelState");
                logger.LogWarning(
                    "ModelState validation failure: {principal}; {method}: {path}; {statusCode}; {result}; {actionArguments}",
                    context.HttpContext.User.Identity.Name, context.HttpContext.Request.Method,
                    context.HttpContext.Request.Path, result.StatusCode,
                    JsonConvert.SerializeObject(result.Value),
                    JsonConvert.SerializeObject(context.ActionArguments));
            }
            else
            {
                await next();
            }
        }
    }
}