I have managed to successfully clone an EF entity using serialization and deserialization. If I set the EntityKey to nothing, I can add it to the context. But when I try to SaveChanges, I get an error saying that the primary key must be unique. This makes sense since the clone has the same key. So I need to change it beforehand.
But the primary key is autoassigned by the DB (SQLite) upon insertion, and since the PK is not nullable I cannot set NewEntity.ID=Nothing, which I presume would tell the context that this entity should receive a temporary key until it is inserted.
If I set NewEntity.ID = 30804328 or some arbitrary (unused) number, it will save to DB fine. But I am very unkeen to query for an unused ID value every time I want to clone an entity.
I understood that the context would treat a detached entity as new when it was 'AddObject'ed, and assign it a temporary key so the DB could do the assignment and then the context would receive the updates. Is this not the case?
How do I resolve this? Thanks for any advice!
I FOUND THE SOLUTION FINALLY. The problem was that the table involved had a primary key identity but Autoincrement was not set. It appears that though the ID key is zero by default when creating a new entity, and it cannot be changed by assignment, it is auto-assigned in the case that Autoincrement is set. But clearly this cannot be resolved automatically if autoincrement (or computed) is not set.