Server-generated keys and server-generated values are not supported by SQL Server Compact

So I understand that CE doesn't support server-generate values - thats alright, I am providing my own with this code...

 public static class ExtensionMethods
    {
        public static TResult NextId<TSource, TResult>(this ObjectSet<TSource> table, Expression<Func<TSource, TResult>> selector)
        where TSource : class
        {
            TResult lastId = table.Any() ? table.Max(selector) : default(TResult);

            if (lastId is int)
                lastId = (TResult)(object)(((int)(object)lastId) + 1);
            return lastId;
        }
    }


  private void AddProperty()
        {
            Property p = new Property();     

            entities.AddToProperties(new Property()
            {
            ID = entities.Properties.NextId(u => u.ID),
            AgentName = "Agent Name",
            Address = "New Property",
            AuctioneerName = "Auctioneer Name",
            SaleTitle = "Sales Title",
            DateOfAuction = null,
            ReservePrice = null,
            CurrentBid = null,
            PreviousBid = null,
            });
            entities.SaveChanges();
            BindData();
        }

Only issue is that this doesn't fix the problem when I think it should. I have 2 tables. One called Property, the other called Image. The ID of both is set to primary key, unique yes, and identity to false. I can't see what I am doing wrong to get this error still, all other fields are set to nullable but 开发者_运维问答I don't think this has anything to do with this error...

Found the solution, it turned out my Identity value couldn't be edited manually, I had to re-generate the database creating it through the model first.