實體框架 | 錯誤：InvalidCastException：System.Int32 類型的字段必須是字符串、數組或 ICollection 類型

Question

問題

當我向我的 Home Controller提交（或發布）一個名為 NewsletterSignup 的方法的請求時，我收到以下錯誤。 在我的時事通訊表單提交后以及在調用此方法並創建捕獲表單數據的 object 之前提示錯誤，從而造成難以排除故障的情況，並確定此確切問題正在傳播的位置。

錯誤

處理請求時發生未處理的異常。

InvalidCastException : System.Int32 類型的字段必須是字符串、數組或 ICollection 類型。 ... System.ComponentModel.DataAnnotations.MaxLengthAttribute.IsValid（對象值）

... System.ComponentModel.DataAnnotations.ValidationAttribute.IsValid（對象值，ValidationContext 驗證上下文）

... System.ComponentModel.DataAnnotations.ValidationAttribute.GetValidationResult（對象值，ValidationContext 驗證上下文）

文件

AppDbContext.cs

應用程序數據庫上下文

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; }
    }
}

集合模型.cs

查看 index.cshtml 和共享 newsletter.cshtml 視圖上使用的 Model

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

時事通訊.cs

時事通訊查看 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
    }
}

家庭控制器.cs

主頁 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

通訊表單的共享視圖

@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>

目標

想要確定此錯誤從何處傳播，以便可以相應地調試有問題的異常。 任何建議或方向肯定會受到贊賞。

• 提前感謝和歡呼。

Answer 1

MaxLenght 屬性用於字符串

    [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

獲取數組或字符串數據的最大允許長度。

Answer 2

Maxlengh 屬性在您的代碼中造成問題。您在發布、刪除或獲取時可能不會遇到任何問題，但在更新或編輯時會彈出錯誤。只需擺脫該屬性添加遷移和更新數據庫。