Monday, September 15, 2008

Database Schema Rowsets

Let's make a small detour here, now that we have mastered the IRowset, and take a brief look at database schema rowsets. The OLE DB specification requires that providers expose a set of rowsets that contain information about the database schema. You can find information about the existing tables, columns, constraints and more (depending on your provider).

Rowset schemas are created by IDBSchemaRowset, an optional Session interface that is supported by SQL Compact, through the GetRowset method. When calling this method, you must specify the rowset schema GUID and an array of VARIANTs containing restrictions that will filter the output of the rowset (each rowset has its own set of restrictions). Each restriction value corresponds to a column in the schema rowset and is either empty (VT_EMPTY), meaning no filtering will occur, or has a value of a type compatible with the column's (see here) by which the rowset will be filtered.

To illustrate this, I adapted the last sample code so that it displays the TABLES schema rowset. The very simple implementation is on the CSchemaRowset (base class) and the CTablesRowset classes.

Sample code:

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