Linq-to-Sql中的顺序GUID？

Question

我刚刚阅读了一篇关于NHibernate从系统时间(Guid.Comb)创建GUID的能力的博客文章,从而避免了大量的数据库碎片.您可以将其称为客户端等效于SQL Server顺序ID.

有没有办法在Linq-to-Sql项目中使用类似的策略(通过在代码中生成Guid)？

Answer 1

C#(安全)代码(NHibernate Guid Comb Generator的赞美)

Guid GenerateComb()
{
    byte[] destinationArray = Guid.NewGuid().ToByteArray();
    DateTime time = new DateTime(0x76c, 1, 1);
    DateTime now = DateTime.Now;
    TimeSpan span = new TimeSpan(now.Ticks - time.Ticks);
    TimeSpan timeOfDay = now.TimeOfDay;
    byte[] bytes = BitConverter.GetBytes(span.Days);
    byte[] array = BitConverter.GetBytes((long) (timeOfDay.TotalMilliseconds / 3.333333));
    Array.Reverse(bytes);
    Array.Reverse(array);
    Array.Copy(bytes, bytes.Length - 2, destinationArray, destinationArray.Length - 6, 2);
    Array.Copy(array, array.Length - 4, destinationArray, destinationArray.Length - 4, 4);
    return new Guid(destinationArray);
}

github上的源代码链接:https: //github.com/nhibernate/nhibernate-core/blob/master/src/NHibernate/Id/GuidCombGenerator.cs

Answer 2

COMB按以下方式生成:

DECLARE @aGuid UNIQUEIDENTIFIER

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

转录为C#的内容如下所示:

    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 );
    }