Entity Framework Adding Existing Item Causes Clone

Question

I'm using the Entity Framework v4 for a small project. Normally I use NHibernate. My issue is that I accidentally had code which added an object which was already persisted to the DB Context's collection, and when I did a SaveChanges(), the EF made a copy of the object, giving it a new Primary Key.

While this is useful, it's not what I wanted. Is there a way to turn off that functionality, and instead have an exception thrown?

UPDATE: CODE NOW INCLUDED

public class CcUser
{
    public int Id { get; set; }
    [StringLength(50)]
    public string TrackingId { get; set; }
    [StringLength(50)]
    public string MembershipGuid { get; set; }

    public bool CookiesConfirmed { get; set; }
    [StringLength(200)]
    public string Email { get; set; }

    public DateTime Modified { get; set; }

}

public class MyDbContext : DbContext
{
    public DbSet<CcUser> Users { get; set; }

}

MyDbContext db = new MyDbContext();

var ccUser = db.Users.FirstOrDefault(u => u.TrackingId == id);   
ccUser.Modified = DateTime.UtcNow;
db.Users.Add(ccUser);
db.SaveChanges();

Can you show the code wich caused the issue?

Ladislav Mrnka
– Ladislav Mrnka

2010-11-18 00:16:04 +00:00
Commented Nov 18, 2010 at 0:16 — Ladislav Mrnka
– Ladislav Mrnka, Commented Nov 18, 2010 at 0:16

Shiraz Bhaiji · Accepted Answer · 2010-11-17 21:31:41Z

1

How do you know that it was the same object?

For example if it was because it had the same name, then you could add a unique index on the name field. That way adding a duplicate row would throw an exception.

answered Nov 17, 2010 at 21:31

Shiraz Bhaiji

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1 Comment

Josh Pearce Over a year ago

It had the same primary key. I retrieved it with a FirstOrDefault, modified one non-key property, and added to the list, and saved. The result was another object, rather than an exception.

Dave Lowe · Accepted Answer · 2010-11-18 18:26:43Z

1

Did you try it without the line to add the ccuser (eg the penultimate line). If the object is already attached to the context, savechanges() should persist the changes. If that doesn't work then try calling detectchanges() before savechanges().

answered Nov 18, 2010 at 18:26

Dave Lowe

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2 Comments

Josh Pearce Over a year ago

I know that, but if I accidentally add an existing object I want EF to throw a PK collision exception not overwrite my PK and clone!

Dave Lowe Over a year ago

is your primary key an identity column? if so then i think ef code-first will mark it as store generated and any attempt to add an entity will ignore any previously set value. i think you'll either have to first check if an entity exists with that primary key and update the relevant entity or try to attach a detached entity to the context. add does what it's name suggests

layonez · Accepted Answer · 2016-05-26 12:18:37Z

0

For everyone who run into that problem:

Method .Add marking entity with EntityState.Added. And when you add existent in context item EF would consider it as a new object because of the Lazy Loading.

And afterwards context.SaveChanges() will generate new primary key for added item and save it to DB.

Use AddOrUpdate if you dont need that feature.

Here related question on MSDN

answered May 26, 2016 at 12:18

layonez

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