ASP.NET MVC Page Validation Fails (The value is invalid.) - asp.net

Question

I'm trying to create ASP.NET MVC Application with Entity Framework, which has One to Many relationship. For that I have successfully managed to load the appropriate list of items to a dropdown control (in Create view), But when I click the Create button (in Create view) page validation is faild, validation error message is The value '1' is invalid..
Error
Model
public class Post
{
public int Id { get; set; }
...
public virtual Person Author { get; set; }
}
DataBaseContext
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
modelBuilder.Entity<Post>()
.HasOptional(p => p.Author);
}
Controller
public ActionResult Create()
{
PopulateAuthorDropDownList();
return View();
}
[HttpPost]
public ActionResult Create(Post post)
{
if (ModelState.IsValid)
{
db.Posts.Add(post);
db.SaveChanges();
return RedirectToAction("Index");
}
PopulateAuthorDropDownList(post.Author);
return View(post);
}
private void PopulateAuthorDropDownList(object selectedPerson = null)
{
var personQuery = from d in db.People
orderby d.Name
select d;
ViewBag.Author = new SelectList(personQuery, "Id", "Name", selectedPerson);
}
View
<div class="editor-label">
#Html.LabelFor(model => model.Author)
</div>
<div class="editor-field">
#Html.DropDownList("Author", String.Empty)
#Html.ValidationMessageFor(model => model.Author)
</div>
When I check Author table in database there is Record with Id 1, so I guess 1 is a valid value. What am I missing here?
Thanks in advance...

Answer 1

You didn't show how the Author object looks like,
Suppose if it is like this,
public class Author
{
public int Id{get;set;}
public string Name{get;set;}
}
Try this,
<div class="editor-label">
#Html.LabelFor(model => model.Author)
</div>
<div class="editor-field">
#Html.DropDownListFor(model => model.Author.Id, ViewBag.Author, "Select an Author")
#Html.ValidationMessageFor(model => model.Author)
</div>

Answer 2

Managed to fix this by
changing Model to
public class Post
{
public int Id { get; set; }
...
public int Author { get; set; } // changed type to int
}
changing View to
<div class="editor-label">
#Html.LabelFor(model => model.Author)
</div>
<div class="editor-field">
#Html.DropDownList("AuthorId", String.Empty)
#Html.ValidationMessageFor(model => model.Author)
</div>
changing Controller to
private void PopulateAuthorDropDownList(object selectedPerson = null)
{
var personQuery = from d in db.People
orderby d.Name
select d;
ViewBag.AuthorId = new SelectList(personQuery, "Id", "UserName", selectedPerson); //Changed Author to AuthorId
}
and removing
modelBuilder.Entity<Post>()
.HasOptional(p => p.Author);
from DataBaseContext
Anyway Thanks for the answers... :)

Answer 3

You should have something like this:
<div class="editor-label">
#Html.LabelFor(model => model.Author.Name)
</div>
<div class="editor-field">
#Html.DropDownListFor(model => model.Author.Name, (SelectList)ViewBag.AuthorList)
#Html.ValidationMessageFor(model => model.Author.Name)
</div>
Note that you should name ViewBag.AuthorList instead of ViewBag.Author

Answer 4

You have to provide a list of options to DropDownList where you are just passing string.empty.
And i You should use the strongly typed version DropDownListFor:
#Html.DropDownListFor(model => model.Author.Name, Model.AuthorList)
Or maybe even better by not using the name but the Id:
#Html.DropDownListFor(model => model.Author.Id, Model.AuthorList)
And your model:
class Model {
...
public SelectList AuthorList {get;set;}
}
And in your controller:
model.AuthorList = new SelectList(fetchAuthors()
.Select(a => new SelectListItem {
Text = a.Name,
Value = a.Id
}, "Value", "Text");