In many applications, we may need to perform queries to retrieve metadata about the database we are connected to. Common examples include retrieving a list of tables in the database, or retrieving a list of columns and column attributes in a table. DTL supports this by providing access to the ODBC catalog functions as though these were regular queries. As an example, here is how one would retrieve a list of tables and basic details using the ODBC SQLTables function:
// Call SQLTables to get a list of tables and descriptions from the DB DynamicDBView<> view("_SQLTables", ""); DynamicDBView<>::sql_iterator it = view.begin(), end_it = view.end(); // Print titles of returned columns vector <tstring> cols = it.GetBoundIOs().GetColumnNames(); copy(cols.begin(), cols.end(), ostream_iterator<tstring>(cout," ")); cout << endl; // Print result of query copy(it, end_it, ostream_iterator<variant_row>(cout,"\n"));
In general, to call an ODBC catalog function we create a query that begins with an underscore, followed by the name of the function we wish to call and a comma seperated list of arguments. (Any trailing arguments that are ommitted are assumed to be empty strings). The currently supported catalog functions with arguments are:
_SQLTables, TableName, SchemaName, CatalogName _SQLColumns, ColumnName, TableName, SchemaName, CatalogName
To add more catalog function to this list, see CallCatalogFunction() in DBStmt.cpp
For details about the ODBC catalog functions see the ODBC documentation.
Note that you may also need to #define DTL_VARIANT_USE_FIXED_LEN_STRING to use a DynamicDBView with these ODBC catalog functions, depending on how your ODBC driver handles strings. See sql_iterator  for details.
Copyright © 2002, Michael Gradman and Corwin Joy.
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