ASP.NET Core 8 Web API data validation ignores data annotations

Question

I'm trying to get automatic data validation working in an ApiController but when the user sends incorrect/missing data a JSON deserialization failed error message is returned instead of the custom ErrorMessage.

ProfilesController.cs

using ClassLibrary.Models;
using ClassLibrary.Services;
using Microsoft.AspNetCore.Mvc;
using Swashbuckle.AspNetCore.Annotations;
using ClassLibrary.Models.API.Responses.Profiles;
using ClassLibrary.Models.API.Requests;
using Microsoft.AspNetCore.Authorization;

namespace API.Controllers
{
    [ApiController]
    [Route("v1/[controller]")]
    public class ProfilesController : Controller
    {
        private IProfileManager _profileManager;

        public ProfilesController(IProfileManager profileManager)
        {
            _profileManager = profileManager;
        }

        [Authorize]
        [HttpPatch("about")]
        public async Task<IActionResult> UpdateAbout([FromBody] UpdateAboutPayload payload)
        {
            await _profileManager.UpdateAboutAsync(payload.About);

            return Ok();
        }
    }
}

UpdateAboutPayload.cs

using System.ComponentModel.DataAnnotations;

namespace ClassLibrary.Models.API.Requests
{
    public class UpdateAboutPayload
    {
        [Required(ErrorMessage = "About is required")]
        [StringLength(500, ErrorMessage = "About must be between 0 and 500 characters long")]
        public required string About { get; set; }
    }
}

When I send the following data

{}

I get this error

{
  "type": "https://tools.ietf.org/html/rfc9110#section-15.5.1",
  "title": "One or more validation errors occurred.",
  "status": 400,
  "errors": {
    "$": [
      "JSON deserialization for type 'ClassLibrary.Models.API.Requests.UpdateAboutPayload' was missing required properties, including the following: about"
    ],
    "payload": [
      "The payload field is required."
    ]
  },
  "traceId": "00-402c938fa2cb172de6a89b521f8fcae1-88ebfe9d6c674e35-00"
}

instead of the error message configured in the [Required] attribute

iKingNinja · Accepted Answer · 2024-04-24 00:18:58Z

1

The issue was caused by the required modifier on the About property, removing it solved the error.

answered Apr 24, 2024 at 0:18

iKingNinja

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2 Comments

Pankaj Over a year ago

This doesn't solves your issue, it just hides it.

iKingNinja Over a year ago

How doesn't it solve my issue? The value is still required but it's set as such by the [Required] attribute instead of the required modifier.

Pankaj · Accepted Answer · 2024-04-24 10:25:33Z

0

That is the correct behavior, you are not sending the whole object, hence you are getting the exception that payload field is required, If you only want "About is required" message, you need to send blank payload, something like this

{ 
   payload: {} 
}

edited Apr 24, 2024 at 10:25

answered Apr 23, 2024 at 21:39

Pankaj

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3 Comments

iKingNinja Over a year ago

About is a string, not an object and even if I set it to an empty object i still get the same error message.

Ben Hutchison Over a year ago

Does this mean that [FromBody] is trying to extract a child property with the key payload from inside your top-level body JSON object, instead of treating the entire body JSON object as an UpdateAboutPayload object itself? Maybe removing [FromBody] will parse the entire body as that class? (Case 6 in Binding Precedence)

iKingNinja Over a year ago

The issue still happens even without the [FromBody] attribute

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