利用asp.net实现生成不重复订单号

#region 生成单据号 
/// <summary> 
/// 生成单据号 
/// </summary> 
/// <param name="pFromType"></param> 
/// <returns></returns> 
public static string GetFormCode(FormType pFromType) 
{ 
string formcode = ""; 
switch(pFromType) 
{ 
case FormType.CaiGou: 
{ 
formcode = "CG"; 
break; 
} 
case FormType.ChaiXie: 
{ 
formcode = "CX"; 
break; 
} 
case FormType.ChuKu: 
{ 
formcode = "CK"; 
break; 
} 
case FormType.LingLiao: 
{ 
formcode = "LL"; 
break; 
} 
case FormType.PeiChang: 
{ 
formcode = "PC"; 
break; 
} 
case FormType.RuKu: 
{ 
formcode = "RK"; 
break; 
} 
case FormType.ShengChan: 
{ 
formcode = "SC"; 
break; 
} 
case FormType.SunYi: 
{ 
formcode = "SY"; 
break; 
} 
case FormType.TuiHuo: 
{ 
formcode = "TH"; 
break; 
} 
case FormType.XiaoShou: 
{ 
formcode = "XS"; 
break; 
} 
case FormType.PeiSong: 
{ 
formcode = "PS"; 
break; 
} 
case FormType.ZengPin: 
{ 
formcode = "ZP"; 
break; 
} 
case FormType.FuKuan: 
{ 
formcode = "FK"; 
break; 
} 
case FormType.ShouKuan: 
{ 
formcode = "SK"; 
break; 
} 
} 
formcode += DateTime.Now.Year.ToString(); 
formcode += DateTime.Now.Month.ToString().Length == 1?"0" + DateTime.Now.Month.ToString() : DateTime.Now.Month.ToString(); 
formcode += DateTime.Now.Day.ToString().Length == 1?"0" + DateTime.Now.Day.ToString() : DateTime.Now.Day.ToString(); 
formcode += DateTime.Now.Hour.ToString().Length == 1?"0" + DateTime.Now.Hour.ToString() : DateTime.Now.Hour.ToString(); 
formcode += DateTime.Now.Minute.ToString().Length == 1?"0" + DateTime.Now.Minute.ToString() : DateTime.Now.Minute.ToString(); 
formcode += DateTime.Now.Second.ToString().Length == 1?"0" + DateTime.Now.Second.ToString() : DateTime.Now.Second.ToString(); 
if(DateTime.Now.Millisecond.ToString().Length == 1) 
{ 
formcode += "00" + DateTime.Now.Millisecond.ToString(); 
} 
else if (DateTime.Now.Millisecond.ToString().Length == 2) 
{ 
formcode += "0" + DateTime.Now.Millisecond.ToString(); 
} 
else 
{ 
formcode += DateTime.Now.Millisecond.ToString(); 
} 
return formcode; 
} 
#endregion