Question

我有一个表有一些列，有时会有一个空值。如何检查值是否为空，如果是，则将值设置为空字符串或稍后可以使用的内容？

private DateTime dtDate_Ordered;
private DateTime dtDate_Required;
private DateTime dtDate_Received;

var stringSql = "select * from po where po_num=" + stringPO_NUM;

var Class_Connection = new SQL_Connection();

Class_Connection.cnn.Close();
Class_Connection.cnn.Open();

try
{
    var cmd = new SqlCommand(stringSql, Class_Connection.cnn);
    SqlDataReader sdr = cmd.ExecuteReader();

    while (sdr.Read())
    {
        dtDate_Ordered = (DateTime)sdr["dateordered"];
        dtDate_Required = (DateTime)sdr["daterequired"];
        dtDate_Received = (DateTime)sdr["daterecv"];
        stringComments = (string)sdr["comments"];
    }
}
catch (Exception Ex)
{
    Class_Connection.cnn.Close();
    throw Ex;
}

Class_Connection.cnn.Close();

RDI_Date_Ordered.SelectedDate = dtDate_Ordered;
RDI_Date_Required.SelectedDate = dtDate_Required;
RDI_Date_Received.SelectedDate = dtDate_Received;

我希望能够在异常处理程序捕获之前处理null值。

Answer 1

重新定义顶部的日期时间可以为空，例如

private DateTime? dtDate_Ordered;

然后当你从阅读器中分配它时，null不会有问题。

if(sdr["dateordered"]==DbNull.Value)
    dtDate_Ordered=null
else
    dtDate_Ordered=sdr.GetDateTime(sdr.GetOrdinal("dateordered"))

Answer 2

在输入值之前，检查每个值以确保它们不为空。

if( sdr["dateordered"] != null)
    dtDate_Ordered = (DateTime)sdr["dateordered"];

if( sdr["daterequired"] != null)
    dtDate_Required = (DateTime)sdr["daterequired"];

if( sdr["daterecv"] != null)
    dtDate_Received = (DateTime)sdr["daterecv"];

stringComments = ( sdr["comments"] == null)? "" : (string)sdr["comments"];

如何在不使用多个读取器的情况下检查SqlDataReader中的空值

2 个答案: