.NET 4.0 Linq to SQL - Object update not working - asp.net-mvc

Question

I'm building a simple MVC Movie Application, using a repository pattern and Class Library for my Linq to SQL Classes. I can't seem to get my objects to UPDATE back to the database.. I'm missing something now sure what it is:
public class MovieRepository : BaseRepository, IMovieRepository
{
/// <summary>
/// Updates the specified movie.
/// </summary>
public void Update()
{
GetDataContext.SubmitChanges();
}
/// <summary>
/// Fetches the by id.
/// </summary>
/// <param name="id">The id.</param>
public Movie FetchById(int id)
{
Movie movie = (from n in GetDataContext.Movies
where n.ID == id
select n).First();
return movie;
}
}
BaseRepository.cs
public abstract class BaseRepository
{
private static VideoStoreDBDataContext _videoStoreDbDataContext;
protected static VideoStoreDBDataContext GetDataContext
{
get
{
if (_videoStoreDbDataContext == null)
{
_videoStoreDbDataContext = new VideoStoreDBDataContext();
}
return _videoStoreDbDataContext;
}
}
}
HomeController
public ActionResult EditMovie(int Id)
{
Movie movie = _movieRepository.FetchById(Id);
if (movie == null)
return RedirectToAction("Error", "Home");
return View(movie);
}
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult EditMovie(Movie movie)
{
if (!ModelState.IsValid)
return View(movie);
// NOTE: movie object does infact contain changes made using the VIEW.
_movieRepository.Update();
return RedirectToAction("Index");
}
View
<% using (Html.BeginForm()) {%>
<fieldset>
<legend>Details</legend>
<p>
<label for="Title">Title:</label><br/>
<%= Html.TextBox("Title", Model.Title) %>
<%= Html.ValidationMessage("Title", "*") %>
</p>
<p>
<input type="submit" value="Update Movie" />
</p>
</fieldset>
<% } %>
<div>
<%=Html.ActionLink("Back to List", "Index") %>
</div>

Answer 1

In your method EditMovie, the object movie that you receive as the argument, is not actually a database-bound object. It gets constructed for you by MVC runtime, and your DataContext has no knowledge of it. Therefore, when you call Update(), the DataContext doesn't see any changes to write to the database.
What you should do instead is find this object in the database, then copy all fields from the method's argument into it, and then call Update(). Like so:
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult EditMovie(Movie movie)
{
if (!ModelState.IsValid)
return View(movie);
var existingMovie = _movieRepository.FetchById( movie.Id );
existingMovie.Title = movie.Title;
_movieRepository.Update();
return RedirectToAction("Index");
}
For this to work, you also have to include your Movie's ID in your form (as a hidden field), so that it may be posted back by the browser, and thus enable you to distinguish update to one movie from update to another. Like so:
<legend>Details</legend>
<p>
<label for="Title">Title:</label><br/>
<%= Html.TextBox("Title", Model.Title) %>
<%= Html.ValidationMessage("Title", "*") %>
<%= Html.HiddenFor( m => m.Id ) %> //<------
</p>
EDIT: As Mystere Man pointed out, you do not need to add this hidden field if your URL contains the Id.

Answer 2

You are forgetting that http is a stateless system. Each page that gets served is a seperate request, and each set of objects are destroyed at the end of each request.
So, the objects returned by your get do not exist in your post, because this is a completely seperate request. In reality, the Default Model Binder is creating a new instance of your Movie object, not modifying the contents of the one you previously returned.
So the update won't work, because L2S doesn't know that your newly created Movie object should be updated.