Ado Entity Framework when should you use attach/detach

Question

Hello,

In ADO.net EF, when should you call the context.Attach() and the context.Detach() methods and how do these calls affect the data being returned or being inserted?

Answer 1

Attaching Objects (Entity Framework)
http://msdn.microsoft.com/en-us/library/bb896271.aspx

Detaching Objects (Entity Framework)
http://msdn.microsoft.com/en-us/library/bb738611.aspx

Answer 2

This is one of those questions where, "If you have to ask, you probably should not be doing it." The Entity Framework will implicitly attach entities in cases where it is obvious that this needs to happen. You really only ever need to explicitly attach and detach entities in cases where you are using more than one ObjectContext at once. Because this can be quite confusing, due to the implicit attachment which happens in the course of normal Entity Framework operations, I strongly recommend that people new to the Entity Framework use only one ObjectContext at a time. If you do this, you should never need to explicitly call Attach or Detach.

Calling, say, Attach does not really affect the data returned, insofar as it's scaler properties are concerned. But if it refers to other entities which are already loaded into the context into which it is attached, then these properties will be pre-populated without explicit loading. That said, entities returned from a query are already attached, so you cannot attach them.