using System;
using System.Data;
using System.Data.SqlClient;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Server;
[Serializable]
[Microsoft.SqlServer.Server.SqlUserDefinedTypeFormat.UserDefined ,IsByteOrdered=true,MaxByteSize =20,ValidationMethodName="ValidateDate")]
public struct date : INullable,IBinarySerialize
{
// 私有成员
private bool m_Null;
private string m_date;
public override string ToString()
{
if (this.m_Null)
return "null";
else
{
return this.m_date;
}
}
public bool IsNull
{
get
{
return m_Null;
}
}
public static date Null
{
get
{
date h = new date();
h.m_Null = true;
return h;
}
}
public static date Parse(SqlString s)
{
if (s.IsNull || (!s.IsNull && s.Value.Equals("")))
return Null;
else
{
date u = new date();
string[] xy = s.Value.Split(" ".ToCharArray());
u.m_date = xy[0];
if (!u.ValidateDate())
throw new ArgumentException ("无效的时间");
return u;
}
}
public string _date
{
get
{
return this.m_date;
}
set
{
m_Null = true;
m_date = value;
if (!ValidateDate())
throw new ArgumentException("无效的时间");
}
}
public void Write(System.IO.BinaryWriter w)
{
byte header = (byte)(this.IsNull ? 1 : 0);
w.Write(header);
if (header == 1)
{
return;
}
w.Write(this.m_date);
}
public void Read(System.IO.BinaryReader r)
{
byte header = r.ReadByte();
if (header == 1)
{
this.m_Null = true;
return;
}
this.m_Null = false ;
this.m_date = r.ReadString();
}
private bool ValidateDate() //判断时间是否有效
{
try
{
DateTime dt = Convert.ToDateTime(m_date);
return true;
}
catch
{
return false;
}
}
}

CREATE TABLE tb(id int,dt dbo.Date DEFAULT CONVERT(dbo.Date,CONVERT(VARCHAR(10),GETDATE(),120)));
insert into tb(id) values(1)
SELECT id,dt=dt.ToString() FROM tb;
/*
结果：
id dt
1 2009-08-14
*/
DROP TABLE tb;