Question 85846 in ASP.NET Question posted in
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Is there a way to override the serialization error message? – Asp.net

I have a simple class for the POST request body:

[Route("api/[controller]")]
[ApiController]
public class TestController : ControllerBase
{
    [HttpPost]
    public IActionResult Post(PostRequest request)
    {
        return Ok();
    }
}

public class PostRequest
{
    [Required]
    public String String { get; set; }
}

If I send an int instead of a string, the following error message is returned:

"$.string": [
"The JSON value could not be converted to System.String. Path: $.string | LineNumber: 1 | BytePositionInLine: 13."] }

I don’t feel like exposing what happens under the hood is right. Is there a way to return a generic "The field String is invalid" message?

Tags:

2

Answers


  1. 0

    I’m not sure, but maybe this will help you. Paste this code at the very beginning of the method:

    if (!ModelState.IsValid)
 {
     return BadRequest();
 }
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  2. 0

    This error comes from System.Text.Json.JsonSerializer inside SystemTextJsonInputFormatter durring desrializing request body into the model and you can disable it like below:

    builder.Services.AddControllers().AddJsonOptions(options =>
    options.AllowInputFormatterExceptionMessages = false);

    And you will relieve error message like this:

    {
  "$.string": [
    "The input was not valid."
  ]
}

    You can also customize error message and get rid of $. like below:

    builder.Services.Configure<ApiBehaviorOptions>(o =>
{
    //we need to call this original factory inside our custom factory
    var originalFactory = o.InvalidModelStateResponseFactory;
    o.InvalidModelStateResponseFactory = context =>
    {
        //get all the keys prefixed with $. (which should be related to json errors)
        var jsonPathKeys = context.ModelState.Keys.Where(e => e.StartsWith("$.")).ToList();
        foreach (var key in jsonPathKeys)
        {
            var normalizedKey = key.Substring(2);
            foreach (var error in context.ModelState[key].Errors)
            {
                if (error.Exception != null)
                {
                    context.ModelState.TryAddModelException(normalizedKey, error.Exception);
                }
                context.ModelState.TryAddModelError(normalizedKey, "The provided value is not valid.");
            }
            context.ModelState.Remove(key);
        }
        return originalFactory(context);
    };
});
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