Problem with SaveChanges() Entity Framework 4.1

Question

I am having problem with saving the changes to database.

I am updating the model A in my controller, however when I save the changes using SaveChanges() I end up having a duplicated item in database for B.

After the UpdateModel() is called I inspected the Bs property and it was as I expected however right after the SaveChanges() is called if I inspect the Bs property I will see that the Id is completely different (new Id and new entry).

My class is similar to this:

public class A
{
    [HiddenInput(DisplayValue = false)]
    public int AId { get; set; }

    public string Name { get; set; }

    public virtual ICollection<B> Bs{ get; set; }
}

public class B
{
    [HiddenInput(DisplayValue = false)]
    public int BId { get; set; }

    public string Name { get; set; }

    public virtual ICollection<A> As{ get; set; }
}

My Controller is like this :

    [HttpPost]
    public ActionResult Edit(A theA)
    {
        try
        {
           db.Entry(theA).State = EntityState.Modified;

           foreach (var item in theA.Bs)
           {
               db.Entry(item).State = EntityState.Modified;
           }

           db.SaveChanges();

           return RedirectToAction("Index");
        }
        catch
        {
            return View();
        }
    }

Am I doing something wrong ?

Thanks in advance

Your controller method would be important to see where you retrieve the objects from DB, modify them and call SaveChanges. — Slauma, Apr 17 '11 at 12:53

score 8 · Accepted Answer · answered Apr 17 '11 at 12:56

8

That is common behavior. The problem is that EF doesn't know that you attached an existing B so it automatically inserts a new record. You must say EF that the B is existing one by calling:

// here add B to the collection in the A and after that call:
dbContext.Entry<B>(someB).State = EntityState.Unchanged();

or by attaching B before you add it to collection in A (I'm not sure if this is possible when using UpdateModel in ASP.NET MVC).

dbContext.Bs.Attach(someB);
// now add B to the collection in the A

Other possibility is to load B from database first and add loaded object to the collection in A but it is additional roundtrip to database.

int id = someB.Id;
var loadedB = dbCotnext.Bs.Single(b => b.Id == id);
someA.Bs.Add(loadedB);
dbContext.As.Add(someA);
dbContext.SaveChanges();

Conclusion: Every time you call Add the whole object graph is tracked as inserted unless you attach related entities first (before you add them to inserted parent - the 2nd and 3rd example) or unless you manually change the state of related entities back to unchanged after adding the parent. (the 1st example).

answered Apr 17 '11 at 12:56

Ladislav Mrnka

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Thanks, I tried the first method, however I get the following message as soon as its called: "AcceptChanges cannot continue because the object's key values conflict with another object in the ObjectStateManager. Make sure that the key values are unique before calling AcceptChanges." – Raha Apr 17 '11 at 14:50
So how did you get your B instance and how did you create your context? Is the context instanced per request and is B with given key used only once (single instance) per context? – Ladislav Mrnka Apr 17 '11 at 14:54
I have added my ActionMethod to the Question, can you please take a look ? – Raha Apr 17 '11 at 17:23
I can now edit without any problem by creating a completely new Context in my action method. Is this correct ? Why can't I keep one context for the whole controller ? – Raha Apr 17 '11 at 18:09
Have you used your controller context for anything else? Is it per request context or globally shared context? – Ladislav Mrnka Apr 17 '11 at 18:54
Before this fix, I was using one context per controller and this didn't work. Then I created a brand new context for my edit action method (inside the method) then this fixed the problem. – Raha Apr 17 '11 at 20:27
But one context per controller actually doesn't answer the question. Did you used a new instance of the context for each request? – Ladislav Mrnka Apr 17 '11 at 21:59
@Ladislav yes I used a new instance context for each request. – Raha Apr 19 '11 at 06:41

Problem with SaveChanges() Entity Framework 4.1

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