c# - Entity Framework |错误 : InvalidCastException: The field of type System. Int32 必须是字符串、数组或 ICollection 类型

Question

问题

当我向 Home Controller 提交(或发布)一个名为 NewsletterSignup 的方法的请求时，我收到以下错误。在提交我的时事通讯表单之后，在调用此方法并创建捕获表单数据的对象之前，会提示错误，从而造成难以排除故障的情况，并确定此确切问题在何处传播。

Error

An unhandled exception occurred while processing the request.

InvalidCastException: The field of type System.Int32 must be a string, array or ICollection type. ... System.ComponentModel.DataAnnotations.MaxLengthAttribute.IsValid(object value)

... System.ComponentModel.DataAnnotations.ValidationAttribute.IsValid(object value, ValidationContext validationContext)

... System.ComponentModel.DataAnnotations.ValidationAttribute.GetValidationResult(object value, ValidationContext validationContext)

文件

AppDbContext.cs

Application Database Context

namespace KingsEye.Data
{
    public class AppDbContext : IdentityDbContext
    {
        public AppDbContext(DbContextOptions<AppDbContext> options) : base(options)  { }

        public DbSet<Home>       Home       { get; set; }
        public DbSet<Pages>      Pages      { get; set; }
        public DbSet<Newsletter> Newsletter { get; set; }
    }
}

CollectionModel.cs

View Model used on index.cshtml and shared newsletter.cshtml view

namespace KingsEye.Models
{
    public class CollectionModel
    {
        public Home       Home       { get; set; }
        public Pages      Pages      { get; set; }
        public Newsletter Newsletter { get; set; }
    }
}

Newsletter.cs

Newsletter View Model

namespace KingsEye.Models
{
    public class Newsletter
    {
        #region Newsletter
        [Display(Name = "Newsletter ID: ")]
        [Required(ErrorMessage = "Newsletter ID Required!")]
        public int     Id     { get; set; }

        [Display(Name = "Full Name: ")]
        [DataType(DataType.Text)]
        public string   Fname  { get; set; }

        [Display(Name = "E-Mail Address: ")]
        [DataType(DataType.EmailAddress)]
        public string   Email  { get; set; }

        [Display(Name = "Phone Number: ")]
        [DataType(DataType.PhoneNumber)]
        public int      Phone  { get; set; }

        [Display(Name = "Active: ")]
        [MaxLength(1)]
        public int      Active { get; set; }

        [Display(Name = "GUID: ")]
        [MaxLength(37)]
        public string   GUID { get; set; }

        [Display(Name = "Created: ")]
        [DataType(DataType.DateTime)]
        public DateTime Create { get; set; }

        [Display(Name = "Updated: ")]
        [DataType(DataType.DateTime)]
        public DateTime Update { get; set; }
        #endregion
    }
}

HomeController.cs

Home Controller

[HttpPost]
public async Task<IActionResult> NewsletterSignup(CollectionModel model)
{ 
    <= Error: is prompting prior to the body of this method being called, 
              and the parameter object being populated with post data!!!

    var newsletter = new Newsletter
    {
        Id     = 0,
        Fname  = model.Newsletter.Fname,
        Email  = model.Newsletter.Email,
        Phone  = model.Newsletter.Phone,
        Active = 0,
        GUID   = Guid.NewGuid().ToString(),
        Create = DateTime.Now,
        Update = DateTime.Now
    };

    ...
}

_Newsletter.cshtml

Shared view for the newsletter form

@model CollectionModel

<div id="newsletter">

    @if (User.Identity.IsAuthenticated)
    {
        <header>
            <i class="far fa-envelope-open"></i>
            <div class="text">Newsletter</div>
            <i class="far fa-envelope-open"></i>
        </header>

        <main>Subscribe to our newsletter</main>

        <footer>
            <form asp-controller="Home" asp-action="NewsletterSignup" method="post" id="newsletter-form" class="text-danger input-form">
                <div asp-validation-summary="ModelOnly"></div>

                <div class="form-group">
                    <input asp-for="@Model.Newsletter.Id" type="hidden" value="0" />
                </div>

                <div class="form-group">
                    <input asp-for="@Model.Newsletter.Fname" id="email-signed" class="form-control" placeholder="Your Name" />
                    <span asp-validation-for="@Model.Newsletter.Fname"></span>
                </div>

                <div class="form-group">
                    <input asp-for="@Model.Newsletter.Email" type="hidden" value="place@holder.com" />
                </div>

                <div class="form-group">
                    <input asp-for="@Model.Newsletter.Phone" id="email-signed" class="form-control" placeholder="(000) 000-0000" />
                    <span asp-validation-for="@Model.Newsletter.Phone"></span>
                </div>

                <div class="form-group input-submit">
                    <input id="newsletter-subscribe" type="submit" value="Subscribe" class="btn material-button" />
                </div>

                <div class="form-group">
                    <input asp-for="@Model.Newsletter.Active" type="hidden" value="0" />
                </div>

                <div class="form-group">
                    <input asp-for="@Model.Newsletter.GUID" type="hidden" value="0" />
                </div>

                <div class="form-group">
                    <input asp-for="@Model.Newsletter.Create" type="hidden" value="0" />
                </div>

                <div class="form-group">
                    <input asp-for="@Model.Newsletter.Update" type="hidden" value="0" />
                </div>

            </form>
        </footer>
    }
    else
    {
        <main>
            Please <a asp-controller="Auth" asp-action="Register">Sign-Up</a> to Subscribe for a Newsletter!
        </main>
    }
</div>

目标

想确定此错误是从哪里传播的，以便可以相应地调试有问题的异常。任何建议或方向肯定会受到赞赏。

提前致谢和欢呼。

Answer 1

MaxLength 属性用于字符串

    [Display(Name = "Active: ")]
    [MaxLength(1)] // this will fail
    public int      Active { get; set; }

    [Display(Name = "GUID: ")] 
    [MaxLength(37)] //this is okay
    public string   GUID { get; set; }

https://docs.microsoft.com/en-us/dotnet/api/system.componentmodel.dataannotations.maxlengthattribute?view=netframework-4.8

Gets the maximum allowable length of the array or string data.