How I can adjust which fields I will have in the response of a model validation (.NET Core Web Api)?

Question

Hi,

I have the following response when there is a validation error;

{
    "type": "https://tools.ietf.org/html/rfc7231#section-6.5.1",
    "title": "One or more validation errors occurred.",
    "status": 400,
    "traceId": "00-ea3f1a67ca3f19d5095b9b671e7b5bff-22418dfbef019280-00",
    "errors": {
        "price": [
            "Price is required for this product code."
        ],
        "quantity": [
            "The quantity must be added.(quantity = 1)"
        ]
    }
}

Actually, I don't need type, title and traceId. How to remove for each response the fields: type, title and traceId. Is there a simple way?

Answer 1

In .NET Core Web API, you can customize the response for model validation errors by implementing a custom ValidationProblemDetails class and overriding the OnSerialize method. This allows you to remove specific fields like "type," "title," and "traceId" from the response.

Here's how you can achieve this:

1. Create a custom ValidationProblemDetails class that inherits from the built-in ValidationProblemDetails class:

using Microsoft.AspNetCore.Mvc;

public class CustomValidationProblemDetails : ValidationProblemDetails
{
    // Override the OnSerialize method to remove unwanted fields
    public override void OnSerialize(Microsoft.AspNetCore.Http.Json.JsonElementWriter writer)
    {
        // Remove the "type," "title," and "traceId" fields from the response
        writer.WriteStartObject();
        writer.WriteEndObject();
    }
}

In your controller, when you want to return a model validation error, use the CustomValidationProblemDetails class:

[ApiController]
public class YourController : ControllerBase
{
    [HttpPost]
    public IActionResult SomeAction([FromBody] YourModel model)
    {
        if (!ModelState.IsValid)
        {
            // Create a new instance of the custom validation problem details
            var problemDetails = new CustomValidationProblemDetails
            {
                Status = 400,
                Title = "One or more validation errors occurred.",
                // Populate the errors dictionary based on your model's validation errors
                Errors = ModelState.ToDictionary(
                    kvp => kvp.Key,
                    kvp => kvp.Value.Errors.Select(e => e.ErrorMessage).ToArray()
                )
            };

            // Return the custom validation problem details
            return new BadRequestObjectResult(problemDetails);
        }

        // Your regular code here for successful processing
        return Ok();
    }
}

In this example, we've created a custom class CustomValidationProblemDetails that inherits from ValidationProblemDetails and overrides the OnSerialize method to remove the unwanted fields from the response. Then, in the controller, we use this custom class to create and return the response for model validation errors.

By using this approach, you can control the fields included in the response for model validation errors and remove the "type," "title," and "traceId" fields as you desired.

Answer 2

Hi,@Cenk

I suggest not to to replace the default bad request response,you could check the document related

The ValidationProblemDetails type:

• Provides a machine-readable format for specifying errors in web API responses.
• Complies with the RFC 7807 specification.

If you insist on replacing the default response,

public class ValidationProblemDetailsResult : IActionResult
    {
        public async Task ExecuteResultAsync(ActionContext context)
        {
            var keys = context.ModelState.Keys;
            var dic = context.ModelState.ToDictionary(
                    kvp => kvp.Key,
                    kvp => kvp.Value.Errors.Select(e => e.ErrorMessage).ToArray()
                );
            var problemDetails = new 
            {
                Status = StatusCodes.Status400BadRequest,                
                Errors= dic
            };
            var objectResult = new ObjectResult(problemDetails) { StatusCode = problemDetails.Status };
            await objectResult.ExecuteResultAsync(context);
        }
    }

configure here in Program.cs:

builder.Services
    .Configure<ApiBehaviorOptions>(x => x.InvalidModelStateResponseFactory = ctx => new ValidationProblemDetailsResult());

Rsult:

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Ruikai Feng