How to set not the ID of the connected entity but the Name field in the Create/Update view?

Question

ASP.NET

Hello connoisseurs.
The bottom line is that there are models:

public class Department
    {
        public int DepartmentID { get; set; }
        public string Name { get; set; }

        public List<Person> Persons { get; set; }
    }
 public class Person
    {
        public int PersonID { get; set; }
        public string Name { get; set; }

        public int DepartmentID { get; set; }
        public Department Department { get; set; }
    }

Well, the context is:

public class DepartmentContext : DbContext
    {
        public DepartmentContext (DbContextOptions<DepartmentContext> options)
            : base(options)
        {
        }

        public DbSet<Department> Department { get; set; }

        public DbSet<Person> Person { get; set; }
    }

VS generated the controller, everything works... When displaying Person, it showed the name and ID of the Department, well, here I corrected everything and shows the name of the Department. But here is the problem with editing and creating. Initially generated controller code:

public IActionResult Create()
        {
            ViewData["DepartmentID"] = new SelectList(_context.Department, "DepartmentID", "DepartmentID");
            return View();
        }
[HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> Create([Bind("PersonID,Name,DepartmentID")] Person person)
        {
            if (ModelState.IsValid)
            {
                _context.Add(person);
                await _context.SaveChangesAsync();
                return RedirectToAction(nameof(Index));
            }
            ViewData["DepartmentID"] = new SelectList(_context.Department, "Name", "Name", person.DepartmentID);
            return View(person);
        }

Well, View:

<div class="form-group">
                <label asp-for="Name" class="control-label"></label>
                <input asp-for="Name" class="form-control" />
                <span asp-validation-for="Name" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="DepartmentID" class="control-label"></label>
                <select asp-for="DepartmentID" class ="form-control" asp-items="ViewBag.DepartmentID"></select>
            </div>
            <div class="form-group">
                <input type="submit" value="Create" class="btn btn-default" />
            </div>

Accordingly, when creating a new person, there will be a page with the name field and DepartmentID drop-down list. I tried and made the dropdown list be named Department, BUT how to save now? gives an error message....

Answer 1

The SelectList constructor has the signature :

public SelectList (System.Collections.IEnumerable items, 
                   string dataValueField, 
                   string dataTextField,
                   object selectedValue);

Therefore, the second parameter must be the name of the property for the values ​​of the option elements:

new SelectList(_context.Department, 
               nameof(Department.DepartmentID), 
               nameof(Department.Name), 
               person.DepartmentID);