add validation filters

Shared/ValidationFilter.cs

@@ -0,0 +1,43 @@
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.Filters;
+using Microsoft.AspNetCore.Mvc.ModelBinding;
+
+namespace Diary.Shared
+{
+	public class ValidationFilter : IAsyncActionFilter
+	{
+		public const string OverviewTitle = "The request is invalid.";
+		public const string OverviewMessage = "The request sent data that is not correct for the request.";
+
+		public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
+		{
+			if (context.ModelState.IsValid)
+			{
+				await next();
+			}
+			else
+			{
+				ValidationExceptionDetails errorObj = new()
+				{
+					Title = OverviewTitle,
+					Message = OverviewMessage,
+					ModelState = GetErrors(context.ModelState)
+				};
+				context.Result = new BadRequestObjectResult(errorObj);
+			}
+		}
+
+		private static List<ValidationProblemDescriptor> GetErrors(ModelStateDictionary modelState)
+		{
+			List<ValidationProblemDescriptor> errors = new();
+
+			return modelState.Where(ms => ms.Value?.Errors.Count > 0)
+					.Select(x => new ValidationProblemDescriptor
+					{
+						Property = x.Key,
+						Errors = x.Value?.Errors.Select(e => e.ErrorMessage).ToArray()
+					})
+					.ToList();
+		}
+	}
+}