The AllowDBNull property determines whether null values can be stored in the column in rows. This value is true by default.
The System.DBNull class must be used to set a column value to null and can test whether a column contains a null value. Using the null keyword results in a runtime error. The following code demonstrates this concept:
DataRow row; // ... retrieve the DataRow // set the value of the first column in the row to null row[0] = DBNull.Value; // test the first column to determine if it contains a null value Boolean isNull = (row[0] == DBNull.Value);
The IsNull( ) method also allows the columns in the DataRow to be tested for null values using a more convenient syntax. The method returns a Boolean value indicating whether the value for the specified column in the row is null.
DataRow row; // ... retrieve the DataRow // test the first column to determine if it contains a null value Boolean isNull = row.IsNull(0);