c# - 非空数据类型的网络核心 : Enforce Required Class Members in Request API Automatically,

Question

我们有 API Controller ，它通过请求 Dto 获取产品数据。要使类成员成为必需，我们需要放置 Required Dto 中的属性。否则服务可以使用空成员执行。
https://docs.microsoft.com/en-us/aspnet/core/mvc/models/validation?view=aspnetcore-3.1
目前有 20 多个成员的 Request DTO，正在写作 [Required]在所有类(class)成员中似乎都非常重复。
我的问题是，为什么需要RequiredAttribute？我们已经有了 int 和 nullable 成员。数据类型本身不应该强制执行契约吗？
有没有办法自动化并让类成员强制执行必需的，而无需到处写？

[HttpPost]
[Route("[action]")]
public async Task<ActionResult<ProductResponse>> GetProductData(BaseRequest<ProductRequestDto> request)
{
    var response = await _productService.GetProductItem(request);
    return Ok(response);


public class ProductRequestDto
{
    public int ProductId { get; set; }
    public bool Available { get; set; }
    public int BarCodeNumber{ get; set; }
    ....

How to add custom error message with “required” htmlattribute to mvc 5 razor view text input editor

public class ProductRequestDto
{
    [Required]
    public int ProductId { get; set; }

    [Required]
    public bool Available { get; set; }

    [Required]
    public int BarCodeNumber{ get; set; }
    ....

Answer 1

如果您愿意使用 Fluent Validation你可以这样做:
此验证器可以使用反射验证任何 dto
验证器:

using FluentValidation;
using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleTests
{
    public class MyValidator : AbstractValidator<ModelDTO>
    {
        public MyValidator()
        {
            foreach (var item in typeof(ModelDTO).GetProperties(System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Instance))
            {
                Console.WriteLine($"Name: {item.Name}, Type: {item.PropertyType}");

                if (item.PropertyType == typeof(int))
                {
                    RuleFor(x => (int)item.GetValue(x, null)).NotEmpty<ModelDTO,int>();
                }
                else
                {
                    RuleFor(x => (string)item.GetValue(x, null)).NotEmpty<ModelDTO, string>();
                }
            //Other stuff...
            }
        }
    }
}

NotEmpty拒绝空值和默认值。
程序.cs

using System;
using System.ComponentModel.DataAnnotations;
using System.IO;

namespace ConsoleTests
{
    class Program
    {
        static void Main(string[] args)
        {

            try
            {
                ModelDTO modelDTO = new ModelDTO
                {
                    MyProperty1 = null, //string
                    MyProperty2 = 0, //int
                    MyProperty3 = null, //string
                    MyProperty4 = 0 //int
                };

                MyValidator validationRules = new MyValidator();
                FluentValidation.Results.ValidationResult result = validationRules.Validate(modelDTO);

                foreach (var error in result.Errors)
                {
                    Console.WriteLine(error);
                }

                Console.WriteLine("Done!");
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
        }
    }
}

输出:

Name: MyProperty1, Type: System.String
Name: MyProperty2, Type: System.Int32
Name: MyProperty3, Type: System.String
Name: MyProperty4, Type: System.Int32
must not be empty.
must not be empty.
must not be empty.
must not be empty.
Done!

对于更完整的解决方案:
看到这个问题 how-to-use-reflection-in-fluentvalidation .
它使用相同的概念，验证器采用 PropertyInfo并通过获取类型和值来进行验证。
以下代码来自上述问题。
属性验证器:

public class CustomNotEmpty<T> : PropertyValidator
{
    private PropertyInfo _propertyInfo;

    public CustomNotEmpty(PropertyInfo propertyInfo)
        : base(string.Format("{0} is required", propertyInfo.Name))
    {
        _propertyInfo = propertyInfo;
    }

    protected override bool IsValid(PropertyValidatorContext context)
    {
        return !IsNullOrEmpty(_propertyInfo, (T)context.Instance);
    }

    private bool IsNullOrEmpty(PropertyInfo property, T obj)
    {
        var t = property.PropertyType;
        var v = property.GetValue(obj);

        // Omitted for clarity...
    }
}

规则生成器:

public static class ValidatorExtensions
{
    public static IRuleBuilderOptions<T, T> CustomNotEmpty<T>(
        this IRuleBuilder<T, T> ruleBuilder, PropertyInfo propertyInfo)
    {
        return ruleBuilder.SetValidator(new CustomNotEmpty<T>(propertyInfo));
    }
}

最后是验证器:

public class FooValidator : AbstractValidator<Foo>
{
    public FooValidator(Foo obj)
    {
        // Iterate properties using reflection
        var properties = ReflectionHelper.GetShallowPropertiesInfo(obj);//This is a custom helper that retrieves the type properties.
        foreach (var prop in properties)
        {
            // Create rule for each property, based on some data coming from other service...
            RuleFor(o => o)
                .CustomNotEmpty(obj.GetType().GetProperty(prop.Name))
                .When(o =>
            {
                return true; // do other stuff...
            });
        }
    }
}