Question

I just read a blog post about NHibernate’s ability to create a GUID from the system time (Guid.Comb), thus avoiding a good amount of database fragmentation. You could call it the client-side equivalent to the SQL Server Sequential ID.

Is there a way I could use a similar strategy in my Linq-to-Sql project (by generating the Guid in code)?

Answer 1

COMBs are generated the following way:

DECLARE @aGuid UNIQUEIDENTIFIER  SET @aGuid = CAST(CAST(NEWID() AS BINARY(10)) + CAST(GETDATE() AS BINARY(6)) AS UNIQUEIDENTIFIER) 

Which transcribed into C# would look like this:

    public static unsafe Guid CombGuid()     {         Guid guid = Guid.NewGuid();         byte[] bytes = guid.ToByteArray();         long ticks = DateTime.Now.Ticks;         fixed( byte* pByte = bytes )         {             int*    pFirst  = (int *)(pByte + 10);             short* pNext    = (short*)(pByte + 14);             *pFirst = (int)(ticks & 0xFFFFFF00);             *pNext  = (short)ticks;         }          return new Guid( bytes );     }