Teach Yourself Borland C++ in 14 Days - portal

436 Day 12
Key Elements
TSession is the central control facility for an application’s database connections. Use the
DatabaseCount property to determine the number of active TDatabases; use the Databases
property to access them by index.
Similar to the Database component’s DatabaseName property, the Session component’s
SessionName property enables you to specify a name to publish to other components. In a
multithreaded application, you would set this property to a name of your choice and then
set the SessionName property of an associated Database and TDataset component (a Table,
Query, or StoredProc) to match. By setting SessionName of a Database and, say, a Query
component to match the one used in a TSession, you specify which database connection the
Query is to use. By extension, if you then interact with Query from within a process thread,
you’ve effectively specified which database connection the thread is to utilize. On some
servers, this is a must because database access in one thread interferes with that of another.
The KeepConnections property determines whether inactive database connections are
retained for temporary TDatabase components. Use DropConnections to drop all inactive
database connections. Keep in mind that if all the current connections to a database server
are inactive and you drop them, you’ll have to log back into the server the next time you need
to access it. There is, however, a way to set KeepConnections to false and still avoid being
prompted for a username and password each time the BDE reconnects to your back end.
(This is covered in the discussion of the Database component later today.)
The location of the BDE network control directory is stored in the NetFileDir property.
Note that this is used for Paradox tables only. The directory path in which temporary files
are located is stored in the PrivateDir property.
Tasks
Use the TSession component when you need to get at the internals of the BDE. You can access
information such as alias lists, alias parameters, and driver settings. You can also make direct
BDE API calls using TSession’s Handle property.
You can use the predefined Session instance variable to call TSession methods. The following
three code excerpts are examples of TSession method calls.
This method call replaces the contents of ListBox1.Items with the list of currently defined
BDE aliases:
Session->GetAliasNames(ListBox1->Items);
This method call replaces the contents of ListBox1.Items with the list of all BDE and
application-specific aliases:
Session->GetDatabaseNames(ListBox1->Items);