为什么 ModelState.IsValid 没有 [Required] 检查模型属性？

Question

我是 ASP 的新手，在 ASP.NET Core (6.0) razorpage 项目中，我发现 ModelState.IsValid 会检查模型的所有属性。比如我有一个模型：

public class SimpleModel
    {
        
        public int Id { get; set; }
        [Required]
        public string Name { get; set; }

        public int Age { get; set; }
    }

和一个页面Example.cshtml，格式为：

@page "/example"
@model StudentManagement.Pages.ExampleModel
@{
    ViewData["Title"] = "Example";
}

<form method="post" class="mt-3">
    <input hidden asp-for="simpleModel.Id" />

    <div class="form-group row">
        <label asp-for="simpleModel.Name" class="col-sm-2 col-form-label">
        </label>
        <div class="col-sm-10">
            <input asp-for="simpleModel.Name" class="form-control" placeholder="Name">
            <span asp-validation-for="simpleModel.Name"></span>
        </div>
    </div>
    <div class="form-group row">
        <label asp-for="simpleModel.Age" class="col-sm-2 col-form-label"></label>
        <div class="col-sm-10">
            <input asp-for="simpleModel.Age" class="form-control" placeholder="Age">
        </div>
    </div>

    <div class="form-group row">
        <div class="col-sm-10">
            <button type="submit" class="btn btn-primary">Update</button>
        </div>
    </div>
</form>

Example.cshtml.cs:

public class ExampleModel : PageModel
    {
        public SimpleModel simpleModel { get; set; }
        public ExampleModel()
        {
            simpleModel = new SimpleModel()
            {
                Id = 1,
                Name = "Tom",
                Age = 15
            };
        }
        public void OnGet()
        {
        }

        public IActionResult OnPost(SimpleModel simpleModel)
        {
            if (ModelState.IsValid)
            {
                this.simpleModel.Age = simpleModel.Age;
                this.simpleModel.Name = simpleModel.Name;
            }
            return Page();
        }
    }

问题是当单击带有空白 Age 的 Update 时，ModelState.IsValid 是错误的。为什么 ModelSate 即使没有 [Required] 也不会忽略 Age？

我试过用int? Age和ModelState.IsValidreturn是的，我还是想知道它是如何工作的。提前致谢。

Answer 1

ModelState.IsValid 表示是否可以将来自请求的传入值正确绑定到模型，以及在模型绑定过程中是否违反了任何明确指定的验证规则。

官方关于non-nullable properties or parameters的解释如下

The validation system treats non-nullable parameters or bound properties as if they had a [Required(AllowEmptyStrings = true)] attribute. By enabling Nullable contexts, MVC implicitly starts validating non-nullable properties or parameters as if they had been attributed with the [Required(AllowEmptyStrings = true)] attribute.

If the app was built with <Nullable>enable</Nullable>, a missing value for Name in a JSON or form post results in a validation error. Use a nullable reference type to allow null or missing values to be specified for the Name property:

您可以参考这篇link了解更多Model validation

为什么 ModelState.IsValid 没有 [Required] 检查模型属性？

Why does ModelState.IsValid check the model properties without [Required]?

c#

asp.net-core

asp.net-core-razor-pages