When inserting data using data callbacks, some databases need to be provided the total length of the inserted value, which requires overriding the RWDBDataCallback::getLength() method.

For ODBC, some drivers require the total length of the data value prior to inserting the value when using data callbacks. Either check the ODBC driver documentation for the SQL_NEED_LONG_DATA_LEN option, or call the function SQLGetInfo() with the SQL_NEED_LONG_DATA_LEN option; if it returns “Y“, the method must be overridden in the derived classes.