使用Entity Framework更新行时出现异常

Question

I get the following exception when trying to update my records:

System.InvalidOperationException: An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key.

The code is as follows: (player is a contract version of player which is passed to method as parameter, ToDbPlayer() is an extension method that takes a contract.Player object and creates an equivalent one for the DB)

using (var context = _contextFactory.CreateEntities())
{
    var dbPlayer = context.Players.Find(player.PlayerId);
    var entity = context.Players.Attach(player.ToDbPlayer()); //here error occurs
    context.Entry(entity).State = dbPlayer == null ? EntityState.Added : EntityState.Modified;
    context.SaveChanges();
}

I'm confused as to what to do - I'm trying to simply update the records in the DB however its falling over when I try to attach it to the context.

I'm not overly confident on my EF skills so if someone can point me in the right direction, it'd be appreciated.

Answer 1

When you do the find the entity will already be attached, so you will not be able to attach it again.

If you need to get the entity without it being tacked use .AsNoTracking() ie

var dbPlayer = context.Players.AsNoTracking().Find(player.PlayerId)