ImprovedGenericUpdateMethod.cs

public virtual void Update(TEntity entityToUpdate)
{
	var entry = this.context.Entry(entityToUpdate);
	var key = this.GetPrimaryKey(entry);
	
	if (entry.State == EntityState.Detached)
	{
		var currentEntry = this.databaseSet.Find(key);
		if (currentEntry != null)
		{
			var attachedEntry = this.context.Entry(currentEntry);
			attachedEntry.CurrentValues.SetValues(entityToUpdate);
		}
		else
		{
			this.databaseSet.Attach(entityToUpdate);
			entry.State = EntityState.Modified;
		}
	}
}