Update entity framework objects

Question

I transfer data between the entity framework and the business layer and user layer by using Data Transfer Objects. I do have some doubt, if I retrieve an object which is converted to a DTO, how do I update the correct object in the entity framework and not just insert a duplicate?

Answer 1

The following code will update an EF 4 entity that has been created as a controller parameter in MVC from a strongly typed view:

It seems the trick is to use the ObjectStateManager to change the state from Added to Modified once the entity has been added to the context.

MyEntities db = new MyEntities(); db.Product.AddObject(product); db.ObjectStateManager.ChangeObjectState(product, System.Data.EntityState.Modified); return db.SaveChanges() > 0; 

As per @Sean Mills comment if you are using EF5 use:

 ((IObjectContextAdapter) db).ObjectContext.ObjectStateManager.ChangeObjectState(entity, System.Data.EntityState.Added); 

Answer 2

an old question, but just in case someone needs a code solution:

http://www.mikesdotnetting.com/Article/110/ASP.NET-MVC-Entity-Framework-Modifying-One-to-Many-and-Many-to-Many-Relationships

Example:

public void EditArticle(         Article article, string articleTypeId, string[] categoryId)  {    var id = 0;    Article art = de.ArticleSet                    .Include("ArticleTypes")                   .Include("Categories")                   .Where(a => a.ArticleID == article.ArticleID)                   .First();    var count = art.Categories.Count;   for (var i = 0; i < count; i++)   {     art.Categories.Remove(art.Categories.ElementAt(i));     count--;   }   foreach (var c in categoryId)   {     id = int.Parse(c);     Category category = de.CategorySet         .Where(ct => ct.CategoryID == id).First();     art.Categories.Add(category);   }    art.Headline = article.Headline;   art.Abstract = article.Abstract;   art.Maintext = article.Maintext;   art.DateAmended = DateTime.Now;    art.ArticleTypesReference.EntityKey = new EntityKey(                                           "DotnettingEntities.ArticleTypeSet",                                            "ArticleTypeID",                                            int.Parse(articleTypeId)                                           );    de.SaveChanges(); }