400 badrequest when passing int instead string in web api .net core 3.1

Question

I need custom message for my request.

Currently I am passing below request json from postman

{
 "countryid": "14sdsads02"
}

but my model is

public class model
{
 public int countryid {get;set;}
}

When pass request from postman, I am getting below error

{
 "type": "https://tools.ietf.org/html/rfc7231#section-6.5.1",
 "title": "One or more validation errors occurred.",
 "status": 400,
 "traceId": "|21793cf-495c68ddbc92ab35.",
 "errors": {
 "$.countryid": [
 "The JSON value could not be converted to System.Int32. Path: $.countryid | LineNumber: 1 | BytePositionInLine: 29."
 ]
 }
}

But instead of this, I need custom error in my web api. How can I achieve this?

• value soft: @PeterCsala . Please under stand i know what is type difference. Only vulnerability purpose i need to stop my property exposing. So how my server level response to customize.
• Peter Csala: Sorry, I misunderstood your question. I left a solution proposal with the desired behaviour.
• Rena: What is the format that you want to custom error?For how to custom error message you could refer to:stackoverflow.com/a/62989600/11398810.

Answer 1

If you want to define a custom response in case of 400 then you can do the followings:

The handler

In order to catch the model binding errors you have to wire up a handler for the ApiBehaviorOptions's InvalidModelStateResponseFactory (1).

The required delegate is quite generic: Func<ActionContext, IActionResult>. So, first let's create an interface for this:

public interface IModelBindingErrorHandler
{
 IActionResult HandleInvalidModelState(ActionContext context);
}

Here is a simple handler implementation:

public class ModelBindingErrorHandler : IModelBindingErrorHandler
{
 private ICorrelationContextAccessor correlationContextAccessor;
 private ILogger logger;
 public ModelBindingErrorHandler(ICorrelationContextAccessor correlationContextAccessor, ILogger logger)
 {
 this.correlationContextAccessor = correlationContextAccessor;
 this.logger = logger;
 }
 public IActionResult HandleInvalidModelState(ActionContext context)
 {
 string correlationId = correlationContextAccessor.CorrelationContext?.CorrelationId;
 var modelErrors = context.ModelState
 .Where(stateEntry => stateEntry.Value.Errors.Any())
 .Select(stateEntry => new InvalidData
 {
 FieldName = stateEntry.Key,
 Errors = stateEntry.Value.Errors.Select(error => error.ErrorMessage).ToArray()
 });
 logger.LogError("The request contained malformed input.", modelErrors);
 var responseBody = new GlobalErrorModel
 {
 ErrorMessage = "Sorry, the request contains invalid data. Please revise.", 
 ErrorTracingId = correlationId
 };
 
 return new BadRequestObjectResult(responseBody);
 }
}

The helper classes

public class GlobalErrorModel
{
 public string ErrorMessage { get; set; }
 public string ErrorTracingId { get; set; }
}
public class InvalidData
{
 public string FieldName { get; set; }
 public string[] Errors { get; set; }
 public override string ToString() => $"{FieldName}: {string.Join("; ", Errors)}";
}

Self-registration

public static class ModelBindingErrorHandlerRegister
{
 /// <summary>
 /// This method should be called after <b>AddControllers();</b> call.
 /// </summary>
 public static IServiceCollection AddModelBinderErrorHandler(this IServiceCollection services)
 {
 return AddModelBinderErrorHandler<ModelBindingErrorHandler>(services);
 }
 /// <summary>
 /// This method can be used to register a custom Model binder's error handler.
 /// </summary>
 /// <typeparam name="TImpl">A custom implementation of <see cref="IModelBindingErrorHandler"/></typeparam>
 public static IServiceCollection AddModelBinderErrorHandler<TImpl>(this IServiceCollection services)
 where TImpl : class, IModelBindingErrorHandler
 {
 services.AddSingleton<IModelBindingErrorHandler, TImpl>();
 var serviceProvider = services.BuildServiceProvider();
 var handler = serviceProvider.GetService<IModelBindingErrorHandler>();
 services.PostConfigure((ApiBehaviorOptions options) =>
 options.InvalidModelStateResponseFactory = handler.HandleInvalidModelState);
 return services;
 }
}

Usage

public partial class Startup
{
 private readonly IConfiguration Configuration;
 public Startup(IConfiguration configuration)
 {
 Configuration = configuration;
 }
 public void ConfigureServices(IServiceCollection services)
 {
 services.AddControllers()
 .AddNewtonsoftJson();
 
 //Omited for brevity
 
 services.AddModelBinderErrorHandler();
 }
 
 //Omited for brevity
}

• value soft: Thanks for your answer. It is worked for me. Bit I didn't understand what is correlationContextAccessor and what is package for this in .net core 3.1
• Peter Csala: @valuesoft It is an external nuget package, called CorrelationId. It helps you to create ids in distributed tracing.

Answer 2

A simple solution is to change type of countryid from int to string in your model"

public class model
{
 public string countryid {get;set;}
}

Then in your controller check if the value is convertible to int or not. If not, return a customized BadRequest response:

int countryid;
if (!int.TryParse(model.countryid, out countryid))
 return BadRequest("Your customized error message");