Cannot remove data record in ASP.NET MVC

Question

First of all, I'm a just beginner, when I trying to delete a record in sql by passing id through view to controller, below is my code:

Note: 'username' is the PK in table "T_Users"

#region Delete record function
        public ActionResult Delete(string id ) {
            T_Users temp_u = new T_Users() { Username = id  };
            //db.T_Users.Attach(new T_Users() { Username = id });
            db.T_Users.Remove(temp_u);


            try
            {
                db.SaveChanges();
                //return View();
            }
            catch(Exception e) {
                return Content("hehe");
            }
            return RedirectToAction("Index");
        }
        #endregion

When I call the T_Users.Attach() method, it said "An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key"

Then I commented that, it failed because "The object cannot be deleted because it was not found in the ObjectStateManager."

Can anybody offer some ideas about the solution?

This issue is about EF, not about ASP.NET MVC. You should not create an object with the ID, you should fetch it and then remove. — Andre Calil
– Andre Calil, Commented Jul 15, 2013 at 13:15
Mn.... but I did the search, didn't find that what about inserting? There are no object because it is new right? — LifeScript
– LifeScript, Commented Jul 15, 2013 at 13:29

Richard · Accepted Answer · 2013-07-15 13:34:30Z

2

you are not retrieving the object from the data context before attempting to delete it, instead you are creating a new detached object assigning the same id as an existing one and attempting to delete it.

You should first retrieve the object you wish to delete from the data context then issue the delete command on the retrieved object. This is an ORM, so you are not simply generating SQL to execute but managing mapped objects.

I hope this helps.

Not a big EF user but you can do something like this with it:

var user = db.T_Users.First(e => e.Username == id);
db.T_Users.Delete(user);

There a a load of EF tutorials like this out there though:

http://www.codeproject.com/Articles/37932/Simple-Sample-with-Entity-Framework

edited Jul 15, 2013 at 13:34

answered Jul 15, 2013 at 13:13

Richard

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2 Comments

Andre Calil Over a year ago

@LifeScript Sorry to ask that, but are you following or reading any EF tutorial?

Andre Calil Over a year ago

@LifeScript I'm much more into NHibernate than into EF, but check this out: msdn.microsoft.com/en-US/data/ee712907 and entityframeworktutorial.net.

Dharman · Accepted Answer · 2021-06-13 11:08:15Z

0

Hi first of all you should get the user form its model ( that is connected to database ) eg : ur model name is User (the _context is the Implementation of data base context eg : i have a database context which name is ShopContext, in ShopContext i have

public class ShopContext : DbContext
{

    public DbSet<User> Users { get; set; }

    public ShopContext(DbContextOptions<ShopContext> options) : base(options)
    {

    }

}

deleted User :

 private readonly ShopContext _context;


 public AdminService(ShopContext context)
 {
    _context = context;
 }

first we inject codes like above then we can create method to delete a use by id

public void deleteUserById(int id)
{
 User user = _context.Users.Find(id);
    _context.Users.Remove(user);
    _context.SaveChanges()

}

edited Jun 13, 2021 at 11:08

Dharman♦

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answered Jun 13, 2021 at 11:02

Soheil vafaei

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