How can I use use Entity Framework to do a MERGE when I don't know if the record exists?

Question

In this SO answer about Entity Framework and MERGE, the example for how to code it is this:

public void SaveOrUpdate(MyEntity entity)
{
  if (entity.Id == 0)
  {
    context.MyEntities.AddObject(entity);
  }
  else
  {
    context.MyEntities.Attach(entity);
    context.ObjectStateManager.ChangeObjectState(entity, EntityState.Modified);
  }
}

This assumes that you already know if the entity that you want to upsert exists or not; in this case you check entity.Id. But what if you don't know if the item exists or not? For instance, in my case, I'm importing records from a vendor into my database, and a given record may or may not have already been imported. I want to update the record if it exists, otherwise add it. But the vendor's id is already set in both cases.

I can't see any way to do this unless I simply ask the database if the record is there already, which defeats the whole purpose of MERGE.

Answer 1

I use AddOrUpdate in this situation. However, I believe it does query the database first in order to decide to issue an insert or update.

context.MyEntities.AddOrUpdate(e => e.Id, entity);

Update:

I ran through my debug log files. First it runs:

SELECT TOP (2) ... WHERE 1 = [Extent1].[Id]

Then it runs either:

INSERT [dbo].[TestTable](...) VALUES (...)
SELECT [Id]
FROM [dbo].[TestTable]
WHERE @@ROWCOUNT > 0 AND [Id] = scope_identity()

OR:

UPDATE [dbo].[TestTable]
SET ...
WHERE ([Id] = @2)

Update 2: Here's an interesting extension method the uses MERGE: https://gist.github.com/ondravondra/4001192