Replace an Entity in Entity Framework Context

I was struggling recently with a problem I KNEW had to be solvable in a much easier way than replacing ALL the fields in my managed entity by hand and then saving it. I wanted a way that I could simply replace the managed entity with a new one that had been created from an XML document.

Turns out it wasn't impossible and my hat goes off to the EF once again.

Basically I had to loop through the XML document creating entities from it and then compare to the DB to see if they already existed. If they did, I had to update them, else I had to add them. A simple query let me know if it existed, but the updating code is where the magic lies:

var oldItem = (from c in entitiesContext.table
               where c.EntityUID == newItem.EntityUID
               select c).FirstOrDefault();

if (oldItem == null)
{
    entitiesContext.table.AddObject(newItem);
}
else
{
    entitiesContext.Detach(oldItem);
    entitiesContext.AttachTo("table", newItem);
    entitiesContext.ObjectStateManager.GetObjectStateEntry(newItem).ChangeState(System.Data.EntityState.Modified);
    entitiesContext.SaveChanges();
}

Voila! Entity replaced and saved from the generated entities.

Now I am by no means a EF guru, but this little trick let me save a TON of time on plumbing as my entities have a lot of fields that need replacing.

WARNING: Be sure the generated entities are accurate, after all, you're removing those in the data and replacing them with the generated ones!