Model binder change validation property name

[petrkasnal]

Hi

I have a question. We are using System.Text.Json in our .NET WebApi project. When I accidentally send a non-valid json to my API (text to number), it will of course return a validation.

{
    "type": "https://tools.ietf.org/html/rfc9110#section-15.5.1",
    "title": "One or more validation errors occurred.",
    "status": 400,
    "errors": {
        "model": [
            "The model field is required."
        ],
        "$.items[0].price": [
            "The JSON value could not be converted to System.String. Path: $.items[0].price | LineNumber: 4 | BytePositionInLine: 24."
        ]
    }
}

Which is fine, of course. However, the name of the property is a bit of a problem for me. Because in our validations we have the property named normally according to the field.

So my question is can I somehow gracefully remove the dollar (root object) from the property name?

Thank you very much

[engineering87]

Hello @petrkasnal,
try to strip the $ from JSON path keys by customizing the InvalidModelStateResponseFactory in ApiBehaviorOptions.

builder.Services.Configure<ApiBehaviorOptions>(options =>
{
    options.InvalidModelStateResponseFactory = context =>
    {
        var newModelState = new ModelStateDictionary();

        foreach (var kvp in context.ModelState)
        {
            var newKey = kvp.Key.StartsWith("$.") ? kvp.Key[2..] :
                         kvp.Key.StartsWith("$") ? kvp.Key[1..] : kvp.Key;

            foreach (var error in kvp.Value.Errors)
                newModelState.AddModelError(newKey, error.ErrorMessage);
        }

        return new BadRequestObjectResult(new ValidationProblemDetails(newModelState)
        {
            Status = StatusCodes.Status400BadRequest
        });
    };
});

This intercepts model state before ValidationProblemDetails is returned, removing the $/$. prefix from property names in the error output.
Let me know.