Check if a database cell is empty first

问题

I am accessing an MS Access 2007 database through C#, and I keep getting an exception whenever I try to read an empty cell.

Specifically, I am trying to read a "Date/Time" cell that may or may not be empty. I am using OLE DB, and have filled a DataSet. None of these conditions work:

DataSet dataSet = GetDataSet();
DataRow row = dataSet.Tables[0].Rows[0];
DateTime time = new DateTime();
time = (DateTime)row[5];   // Exception thrown

How to check if the cell is empty before trying to assign it? None of these work:

if(row[5] == null) ;
if(row[5] == DBNull) ;
if(row[5] == (String)"") ;

Edit: I should have mentioned: When I debug, it says that row[5] equals "System.DBNull,", but I get an error when I try "if(row[5] == DBNULL)". The error says "DBNULL is a type, which is not valid in the given context".

回答1:

You can check it like the following.

if (row[5] == DBNull.Value)
{
    // value is null
}
else if (String.IsNullOfEmpty(Convert.ToString(row[5]))
{
    // value is still null
}
else
{
    // value is not null here
}