Razor 页面：值不会从 OnGet() 停留在 OnPost()

Question

我正在使用 Razor Pages 开发 ASP.NET Core 网页。在一个页面上，添加或选择了一个客户，并且在 OnGet 函数中正确传递了 customer_id（通过调试看到）。当我让用户填写表单时，我尝试使用实体框架调用 SQL 服务器数据库。一切都应该正常工作，但是，在 OnPostAsync() 中，当我尝试导入我在 OnGet() 中设置的 customer_id 值时，我收到一个错误，因为该值以某种方式设置为 0 而不是我之前设置的值.我不知道为什么会发生这种情况，因为我通常是 Razor 页面和实体框架的新手，但我已经发布了下面的代码。任何建议都会很棒！

AddAssessment.cshtml.cs：

namespace CustomerPageTest.Pages.Assessment
{
public class AddAssessmentModel : PageModel
{
    private readonly CustomerPageTest.Data.CustomerPageTestContext _context;

    public AddAssessmentModel(CustomerPageTest.Data.CustomerPageTestContext context)
    {
        _context = context;
    }

    public static List<SelectListItem> InDatabaseUserData()
    {
        List<SelectListItem> Users = new List<SelectListItem>();

            string connString = "Data Source = DESKTOP-5A23I9M; Initial Catalog = DataWarehouse; User ID = sa; pwd = 2128Swan";
            string commandString = "SELECT user_id, name FROM KelderUser";

            SqlConnection conn = new SqlConnection(connString);
            SqlDataAdapter adapter = new SqlDataAdapter(commandString, conn);
            DataTable dtCustomers = new DataTable();
            adapter.Fill(dtCustomers);

            foreach (DataRow dataRow in dtCustomers.Rows)
            {
                SelectListItem temp = new SelectListItem()
                {
                    Value = dataRow[0].ToString(),
                    Text = dataRow[1].ToString()
                };
                Users.Add(temp);
            }
        return Users;
    }

    [BindProperty]
    public CustomerPageTest.Assessment Assessment { get; set; } = new CustomerPageTest.Assessment();
    public List<SelectListItem> SelectUser { get; set; } = new List<SelectListItem>();

    public void OnGet(int customerId)
    {
        SelectUser = InDatabaseUserData();
        Assessment.customer_id = customerId;
        if(Assessment == null)
        {
            return RedirectToPage("/Customer/List");
        }
        return Page();
    }

    // To protect from overposting attacks, enable the specific properties you want to bind to, for
    // more details, see https://aka.ms/RazorPagesCRUD.
    public async Task<IActionResult> OnPostAsync()
    {
        if (!ModelState.IsValid)
        {
            return Page();
        }

        foreach(var item in SelectUser)
        {
            if (item.Selected)
            {
                try { Assessment.user_id = Convert.ToInt32(item.Value); } catch (Exception) { }
            }
        }

        try { Assessment.imported_data_datetime = Convert.ToDateTime(Assessment.imported_data_datetime); } catch(Exception) { }
        _context.Assessment.Add(Assessment);
        await _context.SaveChangesAsync();

        return RedirectToPage("/Customer/List");
    }
}

}

然后AddCustomer.cshtml：

@page
@model CustomerPageTest.Pages.Assessment.AddAssessmentModel

@{
    ViewData["Title"] = "AddAssessment";
}

<h1>AddAssessment</h1>

<h4>Assessment</h4>
<hr />
<div class="row">
    <div class="col-md-4">
        <form method="post">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <div class="form-group">
                <label asp-for="Assessment.vcenter" class="control-label"></label>
                <input asp-for="Assessment.vcenter" class="form-control" />
                <span asp-validation-for="Assessment.vcenter" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Assessment.imported_data_datetime" class="control-label"></label>
                <input asp-for="Assessment.imported_data_datetime" class="form-control" />
                <span asp-validation-for="Assessment.imported_data_datetime" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Assessment.notes" class="control-label"></label>
                <input asp-for="Assessment.notes" class="form-control" />
                <span asp-validation-for="Assessment.notes" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Assessment.user_id"></label>
                <select class="form-control" asp-for="Assessment.user_id" asp-items="Model.SelectUser">
                    <option value="">Select a User</option>
                </select>
            </div>
            <div class="form-group">
                <input type="submit" value="Create" class="btn btn-primary" />
            </div>
        </form>
    </div>
</div>

<div>
    <a asp-page="/Customer/List">Back to List</a>
</div>

@section Scripts {
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}

另外，如果您对我的代码中发生的事情有任何疑问，请告诉我，因为在此之前还有其他类和页面。主要思想是我有一个带有整数的评估类：customer_id，需要设置但没有设置。

Answer 1

发生这种情况的原因是因为 HTTP 是无状态的。一旦处理了该请求，您在一个请求中创建的任何状态（数据）都会被销毁，除非您采取措施将其持久化。

在 Razor 页面 (https://www.learnrazorpages.com/razor-pages/state-management) 中有多种管理状态的方法，但在您的情况下，您应该使用隐藏的表单字段，将选定的客户 ID 发布到 OnPost 处理程序

Answer 2

我写了一个demo，发现你没有在cshtml中绑定customer_id，所以你在cshtml.cs中发布日期时，并没有贴上customer_id。可以在cshtml中添加<input hidden asp-for="Assessment.customer_id" class="form-control" />绑定 customer_id。

这是一个演示：

cshtml:

<div class="row">
    <div class="col-md-4">
        <form method="post">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <div class="form-group">
                <label asp-for="Assessment.vcenter" class="control-label"></label>
                <input asp-for="Assessment.vcenter" class="form-control" />
                <span asp-validation-for="Assessment.vcenter" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Assessment.imported_data_datetime" class="control-label"></label>
                <input asp-for="Assessment.imported_data_datetime" class="form-control" />
                <span asp-validation-for="Assessment.imported_data_datetime" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Assessment.notes" class="control-label"></label>
                <input asp-for="Assessment.notes" class="form-control" />
                <span asp-validation-for="Assessment.notes" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Assessment.user_id"></label>
                <select class="form-control" asp-for="Assessment.user_id" asp-items="Model.SelectUser">
                    <option value="">Select a User</option>
                </select>
            </div>
            <input hidden asp-for="Assessment.customer_id" class="form-control" />
            <div class="form-group">
                <input type="submit" value="Create" class="btn btn-primary" />
            </div>
        </form>
    </div>
</div>

cshtml.cs:

public class AddCustomerModel : PageModel
    {
        [BindProperty]
        public Assessment Assessment { get; set; } = new Assessment();
        public List<SelectListItem> SelectUser { get; set; } = new List<SelectListItem>();
        public IActionResult OnGet()
        {
            for (int i = 1; i < 6; i++) {
                SelectListItem temp = new SelectListItem()
                {
                    Value = i+"",
                    Text = "user"+i
                };
                SelectUser.Add(temp);
            }
            Assessment.customer_id = 2;
            Assessment.vcenter = "vcenter";
            return Page();


        }
        public IActionResult OnPost() {
            if (!ModelState.IsValid)
            {
                return Page();
            }
            return Page();
        }
    }

结果：