ASP.Net MVC 3 timestamp is null - asp.net-mvc-3

Question

I building my first MVC project and having problem with handling concurrency.
Web application was working fine (adding, editing and deleting) before I decided to add concurrency handling.
//Entity class Line
public class Line
{
[Key]
[Required(ErrorMessage = "Please enter a line name")]
public string Name { get; set; }
[Required(ErrorMessage = "Please enter a Business Unit name")]
public string BU { get; set; }
[Required(ErrorMessage = "Please enter a Department name")]
public string Department { get; set; }
[Required(ErrorMessage = "Please enter a location of the line")]
public string Location { get; set; }
[Required(ErrorMessage = "Please enter a target output")]
[Range(0.01, double.MaxValue, ErrorMessage = "Please enter a positive target output")]
public int TargetOutput { get; set; }
[Required(ErrorMessage = "Please enter a target yiel")]
[Range(0.01, 1.00, ErrorMessage = "Please enter a positive number in range of 0.01 to 1.00")]
public Double TargetYield { get; set; }
[Timestamp]
public Byte[] Timestamp { get; set; }
}
code from Controller:
// Saves changes to the Line
[HttpPost]
public ActionResult Edit(Line line)
{
if (ModelState.IsValid)
{
repository.SaveLine(line);
TempData["message"] = string.Format("{0} has been saved", line.Name);
return RedirectToAction("Index");
}
else
{
// return to lines list if there is something wrong with the data
return View(line);
}
}
code from Entity Framework repository class ( this part of code is not competed yet, at the moment when concurrency occurred it supposed to just replace timestamp with the one from db and save it again) :
// Save changes to the line or create new one if not exists
public void SaveLine(Line line)
{
// Checking if line with the same name already exists
//Line found = Lines.FirstOrDefault(l => l.Name == line.Name);
string found = Lines
.Select(l => l.Name)
.Where( n => n == line.Name)
.SingleOrDefault();
if (found == null)
{
context.Lines.Add(line);
}
else
{
context.Entry(line).State = System.Data.EntityState.Modified;
}
//context.SaveChanges();
try
{
context.SaveChanges();
}
catch (DbUpdateConcurrencyException ex)
{
var entry = ex.Entries.Single();
var dbvalues = (Line)entry.GetDatabaseValues().ToObject();
line.Timestamp = dbvalues.Timestamp;
context.SaveChanges();
}
}
When I run application in only one tab and trying to edit line entity I'm getting this error:
Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded. Refresh ObjectStateManager entries.
I have debug and check the timestamp value, it is null. But in database is 0x0000000000000814. When in next step timestamp is replaced with the one from database and trying to save again it throws the same exception.
I have not idea where I have made mistake, any help is much appreciated
Excuse me for my English.
Thank you

Answer 1

You need to write your timestamp out to the view to ensure it comes back into your entity.
Html.HiddenFor(o=>o.Timestamp)

Answer 2

It works when I run single instance of application, but when I run two of them for testing concurrency. I get exception which I have handled and replaced timestamp with the one from the db, but same exception raised again even when both of the timestamps are the same:
From immediate window:
?line.Timestamp
{byte[8]}
[0]: 0
[1]: 0
[2]: 0
[3]: 0
[4]: 0
[5]: 0
[6]: 70
[7]: 81
?dbValues.Timestamp
{byte[8]}
[0]: 0
[1]: 0
[2]: 0
[3]: 0
[4]: 0
[5]: 0
[6]: 70
[7]: 81
Why is that? Should it not only raise exception when timestamps are different?

Answer 3

Resolved: It looks like when I try to save again in code it actually still holding old object with old timestamp. I have moved try catch statement to controller and changed to replace timestamp and return Edit View when concurrency occured. Now when user press Save again exception is not throwed and data is saved.