ASP.NET 核心 Web API 必需的属性异常处理

Question

I am using ASP.NET Core for my new REST API project. I've add an ApiExceptionFilter to get any exception non handle by the system.

But the filter couldn't catch the exception from the [Required] property. The request will get 400 response with the message.

{
    "errors": {
        "XXX": [
            "The XXX field is required."
        ]
    },
    "type": "https://tools.ietf.org/html/rfc7231#section-6.5.1",
    "title": "One or more validation errors occurred.",
    "status": 400,
    "traceId": "00-fa92d07cf6c8694c87febb276786aada-6f9327722d0cb84b-00"
}

I want to customize the error message as the ApiExcetionFilter did. I try to implement UseExceptionHandler but didn't get it works.

app.UseExceptionHandler(c => c.Run(async context =>
            {
                var exception = context.Features
                    .Get<Exception>();

                var response = new { error = exception.Message };
                await context.Response.WriteAsJsonAsync(response);
            }));

Do I have to implement other functions or I did something wrong? Thanks

Answer 1

If I'm understanding what you are trying to do, the error is indicating that this is a bad request (response code being 400), rather than an exception. you could create your own custom attribute by extending ValidationAttribute and use it in place of the Required attribute, and throw the exception from within.

Something like this:

    using System;
    using System.ComponentModel.DataAnnotations;

    [AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
    public class RequiredThrowsException : ValidationAttribute
    {
        public RequiredThrowsException(string ErrorMessage = "Some error message here"): base(ErrorMessage) { }

        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            var val = (string)(value);
            if (val is null || string.IsNullOrEmpty(val))
                throw new ArgumentNullException(ErrorMessage);
            return ValidationResult.Success;
        }

This documentation should help with more complex scenarios.

Any exception thrown from within your custom attribute should then be caught by the exception handler.