I get error using @Html.DropDownListFor for edit session, I use it for create method is succes, but when I use in edit method is fail, the error warning like this System.InvalidOperationException: 'There is no ViewData item of type 'IEnumerable' that has the key 'roles_id'.' .

The deail file like this:

Edit.cshtml:

<div class="form-group">
    @Html.LabelFor(model => model.roles, htmlAttributes: new { @class = "control-label col-md-2" })
    <div class="col-md-12">
        @Html.DropDownListFor(model => model.roles_id, (SelectList)ViewBag.RolesList, new { @class = "form-control" })
        @Html.ValidationMessageFor(model => model.roles_id, "", new { @class = "text-danger" })
    </div>
</div>

EmployeeController.cs

// GET: Employee/Edit/{id}
public ActionResult Edit(int id)
{
    AuthDBHandle dbhandle = new AuthDBHandle();
    adminlteDBHandle sdb = new adminlteDBHandle();

    var roles_id = sdb.GetEmployee().Find(smodel => smodel.employee_id == id).roles_id;
    var roles = dbhandle.GetRoles();
    ViewBag.RolesList = new SelectList(roles, "roles_id", "roles", roles_id);

    return View(sdb.GetEmployee().Find(smodel => smodel.employee_id == id));
}

// POST: Employee/Edit/{id}
[HttpPost]
public ActionResult Edit(EmployeeViewModel smodel)
{
    try
    {
        if (ModelState.IsValid)
        {
            adminlteDBHandle sdb = new adminlteDBHandle();
            if (sdb.EditEmployee(smodel))
            {
                ViewBag.Message = "Edit employee is success";
                ModelState.Clear();
                return RedirectToAction("Index");
            }

            return View();
        }
        return View();
    }
    catch
    {
        return View();
    }
}

EmployeeViewModel.cs

namespace adminlte.Models
{
    public class EmployeeViewModel
    {
        [Display(Name = "Employee Id")]
        public int employee_id { get; set; }

        [Required(ErrorMessage = "Fullname is required.")]
        public string fullname { get; set; }

        [Required(ErrorMessage = "Address is required.")]
        [DataType(DataType.MultilineText)]
        public string address { get; set; }

        public string roles { get; set; }

        [Required(ErrorMessage = "Role ID is required.")]
        public int roles_id { get; set; }

        [Required(ErrorMessage = "Email is required.")]
        [EmailAddress(ErrorMessage = "Invalid Email Address")]
        public string email { get; set; }

        public string password { get; set; }
    }
}

I don't know why, I try to look for an example but fail all, please help me to solve this problem.

Thanks.

CodePudding user response：

Data you put in the ViewBag is not persisted between requests. When you try to display your view again, you need to repopulate the ViewBag items.

I generally extract the code to populate the lookups to a separate method, which avoids duplication.

Eg:

private void PopulateLookups(EmployeeViewModel vm)
{
    AuthDBHandle dbhandle = new AuthDBHandle();
    var roles = dbhandle.GetRoles();
    ViewBag.RolesList = new SelectList(roles, "roles_id", "roles", vm.roles_id);
}

// GET: Employee/Edit/{id}
public ActionResult Edit(int id)
{
    adminlteDBHandle sdb = new adminlteDBHandle();
    var employee = sdb.GetEmployee().Find(smodel => smodel.employee_id == id);
    if (model == null) return RedirectToAction("Index");
    
    var vm = new EmployeeViewModel 
    { 
        employee_id = employee.employee_id,
        fullname = employee.fullname,
        address = employee.address,
        roles = employee.roles,
        roles_id = employee.roles_id,
        email = employee.email,
        password = employee.password, // WARNING!
    };
    
    PopulateLookups(vm);
    return View(vm);
}

// POST: Employee/Edit/{id}
[HttpPost]
public ActionResult Edit(EmployeeViewModel vm)
{
    try
    {
        if (ModelState.IsValid)
        {
            adminlteDBHandle sdb = new adminlteDBHandle();
            if (sdb.EditEmployee(vm))
            {
                return RedirectToAction("Index");
            }
        }
        
        PopulateLookups(vm);
        return View();
    }
    catch
    {
        PopulateLookups(vm);
        return View();
    }
}

NB: Based on your column names, you appear to be storing the employees' passwords in plain text. Don't do that! Store a salted hash of the password, using multiple iterations of a cryptographically-secure one-way hashing algorithm.