如何为路由参数错误指定类型转换错误消息？ （C#，WebAPI）

Question

I have a WebApi controller with an action. One of the route parameters gets cast to an enumeration. However, if the caller specifies a value that's invalid, a default error message is returned with the BadRequest HTTP Status. My enum has two valid values: person/org. If I pass in a "p" for example, this is what gets returned:

{
    type: "https://tools.ietf.org/html/rfc7231#section-6.5.1",
    title: "One or more validation errors occurred.",
    status: 400,
    traceId: "|cc923491-4f15cb34f96ad64a.",
    errors: {
        Type: [
            "The value 'p' is not valid for Type."
        ]
    }
}

How can I specify the error message for this cast error? Ideally, I would just specify it with an attribute here in the class definition:

public class Entity
{
    // How do I return this as the error message for an incorrect cast of EntityType?
    // "entityType must be either 'person' or 'org'."
 
    [Required]
    public EntityType Type { get; set; }
    [Required]
    [Range(1, long.MaxValue, ErrorMessage = "Please specify a valid entity id. Value must be an integer greater than 0.")]
    public long Id { get; set; }
}

Answer 1

You can use the EnumDataType attribute but it only work if you specify an integer value that doesn't match any of the EntityType enum values.

[EnumDataType(typeof(EntityType ), ErrorMessage = "Please specify a valid EntityType.")]

Another thing you can do is create a custom ResultFilterAttribute and handle the error:

public class CustomFilter : ResultFilterAttribute
{
    public override void OnResultExecuted(ResultExecutedContext context)
    {
        // your code
        base.OnResultExecuted(context);
    }
}

Note : you have to register the filter in the FilterCollection of your API

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc(options => options.Filters.Add(new CustomFilter()));
}