The data callback classes can be used with ODBC to insert and fetch data. These classes are useful for very large data that may not fit in memory for a single database call and are described in Section 15.3, “The Data Callback Classes,” in the DB Interface Module User’s Guide.

ODBC drivers vary in their capabilities. Some drivers do not support data callbacks used for columns in the select list before the last bound column. There may also be a restriction on the number of rows that can be fetched at one time from a result set, so that calls to RWDBOSql::fetch() may return only one row. Check the documentation for the SQL_GETDATA_EXTENSIONS supported by the ODBC driver for more information.

Multiple rows can be inserted in one call to RWDBOSql::execute(). The number of rows is determined by the entries parameter passed to the constructor of a data callback class or an RWDBTBuffer instance. Please see Chapter 15, “Using the Open SQL Classes,” in the DB Interface Module User’s Guide for information about array input.