Round .NET DateTime milliseconds, so it can fit SQL Server milliseconds

Question

I want to convert the datetime value to the value that I will get from SQL Server 2008.

SQL Server truncate the milliseconds to 3 digits, so I truncate the milliseco

Answer 1

A little late to the party, but here's a solution, based on the SQL Server docs for the datetime datatype for different versions of SQL Server:

• SQL Server 2000
• SQL Server 2005
• SQL Server 2008

For any given date/time value, this should give you exactly the same value as SQL Server will:

public static class DateTimeExtensions
{
                                   //  milliseconds modulo 10:    0    1    2    3    4    5    6    7    8    9
    private static readonly int[]    OFFSET                  = {  0 , -1 , +1 ,  0 , -1 , +2 , +1 ,  0 , -1 , +1 } ;
    private static readonly DateTime SQL_SERVER_DATETIME_MIN = new DateTime( 1753 , 01 , 01 , 00 , 00 , 00 , 000 ) ;
    private static readonly DateTime SQL_SERVER_DATETIME_MAX = new DateTime( 9999 , 12 , 31 , 23 , 59 , 59 , 997 ) ;

    public static DateTime RoundToSqlServerDateTime( this DateTime value )
    {
        DateTime dt           = new DateTime( value.Year , value.Month , value.Day , value.Hour , value.Minute , value.Second , value.Millisecond) ;
        int      milliseconds = value.Millisecond ;
        int      t            = milliseconds % 10 ;
        int      offset       = OFFSET[ t ] ;
        DateTime rounded      = dt.AddMilliseconds( offset ) ;

        if ( rounded < SQL_SERVER_DATETIME_MIN ) throw new ArgumentOutOfRangeException("value") ;
        if ( rounded > SQL_SERVER_DATETIME_MAX ) throw new ArgumentOutOfRangeException("value") ;

        return rounded ;
    }
}

It will not, however, work properly, for smalldatetime or the new datetime2 datatypes.