How to add object to context handling duplicates correctly?

Question

I'm using Entity Framework 4.4 and I have a One-To-Many relationship model like this:

class A { 
   public int Id { get; set; }
   public virtual B { get; set; }
   public int BId;
}
class B {
   public Id { get; set; }
   private ICollection<A> _As;
   public virtual ICollection<A> As
   {
      get { return _As ?? (_As = new HashSet<A>()); }
      protected set { _As = value; }
   }
}

Now, supposing I have 2 A instances, both with the same B instance. Then I'd have something like this (JSON representation):

A: { Id: 1, BId: 1, B: { Id: 1, As: [ 1, 2 ] } }
A: { Id: 2, BId: 1, B: { Id: 1, As: [ 1, 2 ] } }

I want to then cycle through my current list of A instances and add the to the db context:

foreach (var a in LocalAList)
{ 
   dbContext.Add(a);
   dbContext.SaveChanges();
}

The problem is that I get exceptions informing me that I've inserted duplicate objects. I've looked around and found things dealing with Entity modification and attachment, but I'm still pretty new to EF. I would imagine that this is a typical thing and there's an idiom for handling object insertion where the object already exists.

How can I efficiently add new objects to the context while avoiding the addition of duplicates? Should I just capture the duplicate exception and ignore it? Is there a better way to check?

Are the Ids database generated identities? And what exception do you get exactly? An exception about a primary key constraint violation? (In that case you can't have database generated identities, I think...) What do you want to insert exactly? Only the As, or the Bs as well? Or are the Bs existing entities and you want only to create a relationship between new As and existing Bs? — Slauma
– Slauma, Commented Mar 5, 2013 at 18:16
Honestly, I won't answer now anymore. For the sake of fairness to Mark Oreta's answer you should either roll back your edit to the former version and write a new question with your edit, or write a comment under Mark Oreta's answer that you have changed your question to give him a chance to adjust his answer. Your question change is so massive that his answer currently even doesn't make sense anymore. — Slauma
– Slauma, Commented Mar 6, 2013 at 17:51
Agreed @Slauma; see stackoverflow.com/questions/15255898/… — Mike Caron
– Mike Caron, Commented Mar 6, 2013 at 19:05

Mark Oreta · Accepted Answer · 2013-03-05 18:00:46Z

2

You could do a simple test to see if a already exists in the database, the simplest one is to see if the Id is 0. This is because once the A is added to the DB, an Id is given to your entity. At that point, you should just reattach it rather than re-adding it

Example:

foreach (var a in LocalAList)
{ 
  if (a.Id == 0)
    dbContext.Add(a);
   else 
    dbContext.As.Attach(a)

   dbContext.SaveChanges();
}

answered Mar 5, 2013 at 18:00

Mark Oreta

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