如何通过列名在MySqlDataReader中检查NULL? [英] How to check for NULL in MySqlDataReader by the column's name?

问题描述

如何在打开的MySqlDataReader中检查NULL值?

How can I check for a NULL value in an open MySqlDataReader?

以下内容无效；它总是按else:

The following doesn't work; it's always hitting the else:

if (rdr.GetString("timeOut") == null)
{
    queryResult.Egresstime = "Logged in";
}
else
{
    queryResult.Egresstime = rdr.GetString("timeOut");
}

rdr.IsDbNull(int i)仅接受列号，而不接受名称.

rdr.IsDbNull(int i) only accepts a column number, not name.

推荐答案

var ordinal = rdr.GetOrdinal("timeOut");
if(rdr.IsDBNull(ordinal)) {
  queryResult.Egresstime = "Logged in";
} else {
  queryResult.Egresstime = rdr.GetString(ordinal);
}//if

或

if(Convert.IsDBNull(rdr["timeOut"])) {
  queryResult.Egresstime = "Logged in";
} else {
  queryResult.Egresstime = rdr.GetString("timeOut");
}//if

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