从 Netcore 2.2 Web API 的响应中获取错误消息

Question

I call Register method with empty username and password. So I received this result:

{
    "errors": {
        "Password": [
            "The Password field is required.",
            "Password length is between 4 and 8."
        ],
        "Username": [
            "The Username field is required."
        ]
    },
    "title": "One or more validation errors occurred.",
    "status": 400,
    "traceId": "0HLJIO56EGJEV:00000001"
}

My Dto:

public class UserForRegisterDto
{
    [Required]
    public string Username { get; set; }
    [Required]
    [StringLength(8, MinimumLength = 4, ErrorMessage = "Password length is between 4 and 8.")]
    public string Password { get; set; }
}

I only want to get errors attribute from response, What should I do?

Answer 1

This is a new feature in ASP.NET Core 2.2:

An IActionResult returning a client error status code (4xx) now returns a ProblemDetails body.

The docs describe that this can be disabled when calling AddMvc inside of ConfigureServices , like this:

services.AddMvc()
    .SetCompatibilityVersion(CompatibilityVersion.Version_2_2)
    .ConfigureApiBehaviorOptions(options =>
    {
        options.SuppressUseValidationProblemDetailsForInvalidModelStateResponses = true;
    });

This will result in the pre-2.2 behavior, which will serialise only the errors.

Answer 2

As I went through a very close scenario, I will add here an answer just in case others run into the same or similar issues:

In my case, the problem involved a project with .NET Core 3.1 as Target Framework. My project had a NuGet package dll as one of its dependencies and such package had several models. Our controller endpoints had these models as parameters. However, requests sent to any of these endpoints (with any of those models as body) were giving rise to validation errors for non-nullable reference type properties.

The workaround to solve it was similar to the one suggested by Kirk. I have added the following option to AddControllers method, from Startup's ConfigureServices method:

services.AddControllers(options => options.SuppressImplicitRequiredAttributeForNonNullableReferenceTypes = true);

Note that, by using this workaround, it will be necessary to manually add [Required] attributes for nullable reference type properties around your application.

I also opened an issue on their repository: https://github.com/dotnet/aspnetcore/issues/27448