來源:http://blog.csdn.net/beautifulsarah/article/details/54691670
DBNull.Value,, 适用于向資料庫的表中插入空值。而 null,是指在程式中表示空引用。 或者對象為空。就是沒有執行個體化。
row[column]的值為DBNull.Value的話,至少說明它是從資料庫中取到值了,對應了資料庫中的空值;但如果row[column]的值為null的話,說明沒有從資料庫中取到值。DBNull.Value是一個有着記憶體位址的具體類型的值,映射了資料庫中的null值;而NULL則是空指向,不存在對應的記憶體位址。任何對象指派為null後,記憶體就釋放了。
轉換方法:
heper類中:
/// <summary>
/// 将null轉換為DBNull.Value
/// </summary>
/// <param name="value"></param>
/// <returns></returns>
public object ToDbValue(object value)
{
if (value == null)
{
return DBNull.Value;
}
else
{
return value;
}
}
/// <summary>
/// 将DBNull.Value轉換為null
/// </summary>
/// <param name="value"></param>
/// <returns></returns>
public object FromDbValue(object value)
{
if (value == DBNull.Value)
{
return null;
}
else
{
return value;
}
}
應用:
public List<DateJg> GetList(int ncpid, DateTime start, DateTime end)
{
var list = new List<DateJg>();
string sql = @"select * from v_yjdatealljg where yjxzqid=9 and ncpid [email protected] and cjrq>[email protected] and cjrq<[email protected] order by cjrq,yjxzqid,ncpid";
var sqlparms = new SqlParameter[] {
new SqlParameter("@ncpid",ncpid),
new SqlParameter("@start",start.Date),
new SqlParameter("@end",end.Date)
};
var table = helper.ExecuteDataTable(sql, sqlparms);
using (System.Data.IDataReader dataReader = table.CreateDataReader())
{
while (dataReader.Read())
{
list.Add(GetInfo(dataReader));
}
}
return list;
}
private DateJg GetInfo(IDataReader reader)
{
var info = new DateJg();
info.lsjg = (decimal?)helper.FromDbValue(reader["lsjg"]);
info.ncpid = (int)helper.FromDbValue(reader["ncpid"]);
info.ncpmc = (string)helper.FromDbValue(reader["ncpmc"]);
info.pfjg = (decimal?)helper.FromDbValue(reader["pfjg"]);
info.rq = (DateTime)helper.FromDbValue(reader["cjrq"]);
info.ttjg = (decimal?)helper.FromDbValue(reader["ttjg"]);
info.yjxzqid = (int)helper.FromDbValue(reader["yjxzqid"]);
info.yjxzqname = (string)helper.FromDbValue(reader["yjxzqname"]);
return info;
}
轉載于:https://www.cnblogs.com/hao-1234-1234/p/7838608.html