Razor 页面：值不会从 OnGet() 停留在 OnPost()

Question

I'm working on a ASP.NET Core webpage using Razor Pages. On one page, a customer is added or selected and the customer_id is passed through correctly in the OnGet function (seen through debugging). When I then have the user fill out the form, I try to make a call to a SQL server database using Entity Framework. Everything should be working correctly, however, in OnPostAsync(), when I try to import the customer_id value I had set in OnGet(), I get an error because the value somehow gets set to 0 instead of what I had it previously set as. I don't know why this is happening as I'm generally new to Razor Pages and Entity Framework, but I've posted the code below. Any suggestions would be great!

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");
    }
}

}

Then 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");}
}

Also, If you have any questions about what is going on in my code, let me know as there are other classes and pages before this. The main idea is that I have an Assessment class with an integer: customer_id, that needs to be set and it's not getting set.

Answer 1

The reason this happens is because HTTP is stateless. Any state (data) that you created in one request is destroyed once that request has been processed unless you take steps to persist it.

There are multiple ways to manage state in Razor Pages ( https://www.learnrazorpages.com/razor-pages/state-management ), but in your case, you should use a hidden form field, posting the selected customer ID to the OnPost handler

Answer 2

I write a demo,and i find you didn't bind the customer_id in the cshtml,so when you post the date to cshtml.cs,you didn't post the customer_id.You can add <input hidden asp-for="Assessment.customer_id" class="form-control" /> in the cshtml to bind customer_id.

Here is a demo worked:

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();
        }
    }

Result: