CDataSource and CSession

With this post, I'm presenting the first incarnation of the CDataSource and CSession classes on the OLE DB client library. These still bear some similarity to the ATL OLE DB Consumer Templates counterparts (I did stole some variable names, sorry), but you will see some differences. For instance, there is a CDataSource::Create method that can optionally open a CSession object. This means that besides creating the database, you can immediately open a session with it. As always, I'm using the CreateSDF sample to implement this code.

From now on things will start to get a bit more interesting and useful: besides creating or opening a database using OLE DB, we want to access and edit both data and structure. We can do this either through SQL commands or through the exposed interfaces. My next challenge will be to tackle base table cursors and SQL commands. These require the introduction of two other objects that are central to OLE DB programming: the rowset and the accessor. While a rowset represents a set of rows that you can navigate on, an accessor defines how the individual columns are accessed and mapped to your application data. Rowsets are not only used to handle cursor data (both from a table and from a SQL query) but they are also internally used by the OLE DB provider to report other data to the consumer (like schema information). Accessors are required to map data between your application's memory and the provider's data, for three specific purposes:

• Table or query data;
• SQL command parameters;
• Index column data.

Here we will meet some very interesting challenges, like handling the BLOB peculiarities of SQL Compact, but this will be an interesting ride. I promise.