Best way to pass lookup values to a dropdownlist - asp.net-mvc

Question

I'm wondering what's the general approach of passing a list of lookup values to a view in MVC. Currently I have 2 db tables and I'm using db first EF6 to interface. My main table has a lookup table and I want to populate a dropdownlist of my view with all the values of the lookup so that the user can pick when creating and editing.
Employee Table
id primary key
name varchar
department id - this is the id of the department in the lookup
Department table
id primary key
name varchar
Is it best to create a partial class for the employee model and add a new property called allDepartments and then in my controller call a method that gets all the departments before passing the model to the view, or is it better to dump the departments in the viewbag/viewdata dictionary?
What is the general approach here?

Answer 1

You need to create a ViewModel like this:
public class EmployeeViewModel
{
public string Name { get; set; }
[Required(ErrorMessage = "...")] // to protect against under-posting attacks
[Display(Name = "Department")]
public int? DepartmentId { get; set; }
public IEnumerable<SelectListItem> Departments { get; set; }
}
Controller:
public ActionResult Create()
{
var employeeViewModel = new EmployeeViewModel();
employeeViewModel.Departments = GetDepartments().Select(option => new SelectListItem
{
Text = option.name,
Value = option.Id.ToString()
});
return View(employeeViewModel);
}
// Post
public ActionResult Create(EmployeeViewModel model)
{
// Map ViewModel to Entity and Save to db...
}
View:
#model EmployeViewModel
<div class="form-group">
#Html.LabelFor(model => model.Name)
#Html.TextBoxFor(model => model.Name, new { #class = "form-control" })
#Html.ValidationMessageFor(model => model.Name)
</div>
<div class="form-group">
#Html.LabelFor(model => model.DepartmentId)
#Html.DropDownListFor(model => model.DepartmentId, Model.Departments, "Choose...")
#Html.ValidationMessageFor(model => model.DepartmentId)
</div>