Question

I have the following Model

public class CourseModel
{
    [Key]
    public int courseID { get; set; }
    ...
    public virtual ICollection<CourseMeetModel> meets { get; set; }
}

When I try to edit one of the entries and if the input is valid it works fine.
However if the if its not valid it alerts the user of the mistakes. Once the user fixes the mistakes and tries to save i get the following exception.

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 noticed this happens if the input fails the validation steps in my controller.

My Controller

public ActionResult EditCourseConfirmed(CourseModel course)
{
        CoursesDBContext db = new CoursesDBContext();
        bool valid = validateCouse(course); //If this fails and the course model is returned back to the view I get that error
        if (valid)
        {
                try
                {
                    db.Entry(course).State = EntityState.Modified;
                    db.SaveChanges();
                    Session[d.s_Clear] = false;
                    return RedirectToAction("Index");
                }
                catch (Exception e)
                {
                    ModelState.AddModelError(string.Empty, "Unable to save the course, please try again." + e.Message);
                    return View(course);
                }

        }

        return View(course);
}

Answer 1

Try this

try {
   context.SaveChanges();
} 
catch (OptimisticConcurrencyException) 
{
    context.Refresh(RefreshMode.ClientWins, db.table);
    context.SaveChanges();
}

Props: https://stackoverflow.com/a/6848729/1166147

Adding on to explain, per your comments. Thanks for your EF4 CTP5 tip. Glad this fixed it, please mark as accepted. When you get this error, something happened that changed the data (another user, etc) between load and update, there is a trigger causing problems, or if using a stored procedure it hit 0 recs. It is hard to know without more info. Is this the first update hit? Was there another update run first that succeeded before the user hit the error, modified, and then tried to go on without refreshing? Do you have any triggers? What is your degree of concurrency – did another user edit and save between this users’ query and update? Read the link to the post I gave – someone mentioned a ReadOnlyAttribute in an entity key’s metadata being replaced, which causes its value to become zero as a potential cause – I am not sure about this, but it makes sense –

(Modified from MSDN) By default, the Entity Framework implements an optimistic concurrency model. This means that locks are not held on data in the data source between when the data is queried and the data is updated, creating the potential for this error if another user modified the data. When this attribute is used, the Entity Framework checks for changes in the database before saving changes.

Any conflicting changes will cause an OptimisticConcurrencyException.

An OptimisticConcurrencyException can also occur when you define an Entity Data Model that uses stored procedures to make updates to the data source. In this case, the exception is raised when the stored procedure that is used to perform updates reports that zero rows were updated. SET NOCOUNT ON would fix thia.