Entityframework duplicating when calling savechanges

Question

I am using entityframework 5 code first, I have a model like this.

class Product {
    public Product() {
        Fabrics = new BindingList<FabricLineItem>();
    }
    ...
    public virtual ICollection<FabricLineItem> Fabrics { get;set; }
}

class FabricLineItem {
    [ForeignKey("Fabric")]
    public int FabricId { get; set; }  
    public virtual Product Product { get;set; }
    public virtual Fabric Fabric { get;set; }  
}

class Fabric {
    ...
}

I already have fabrics in my database. I create a new product object and add some fabriclineitems to the collection. When I try to save product what happens is it duplicates the fabric in the database and reference it to the new one after calling

 DataContext.SaveChanges(); 

Before the call to savechanges the values in the debugger are correct by after calling they are changed ? Any idea why I am getting this strange behavior ?

Answer 1

I was also having the problem of E.F. not recognising that an item already existed when it was referenced within another new object to be added to the DB.

@NeilThompson gave me the clue above how to solve this:

You need to attach an existing entity to the context so that it knows that it already exists:

For example:

context.Fabrics.Attach(product.Fabric); 
context.Products.Add(product);
context.SaveChanges();

return organisation;

I got this from here:

"If you have an entity that you know already exists in the database but which is not currently being tracked by the context then you can tell the context to track the entity using the Attach method on DbSet. The entity will be in the Unchanged state in the context."

http://blogs.msdn.com/b/adonet/archive/2011/01/29/using-dbcontext-in-ef-feature-ctp5-part-4-add-attach-and-entity-states.aspx