Update entity framework objects - entity-framework

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();
}

Answer 3

//I am replacing player :)
public ActionResult ProductEdit(string Id, Product product)
{
int IdInt = DecyrptParameter(Id);
MyEntities db = new MyEntities();
var productToDetach = db.Products.FirstOrDefault(p=> p.Id == IdInt);
if (product == null)
throw new Exception("Product already deleted"); //I check if exists, maybe additional check if authorised to edit
db.Detach(productToDetach);
db.AttachTo("Products", product);
db.ObjectStateManager.ChangeObjectState(product, System.Data.EntityState.Modified);
db.SaveChanges();
ViewData["Result"] = 1; // successful result
return View();
}

Answer 4

You would need to include a primary or alternate key in the DTO, then match that key back to the correct EF entity upon update.

Answer 5

This should work for EF 5: https://stackoverflow.com/a/11749716/540802:
db.Entry(product).State = EntityState.Modified;