Teach Yourself Borland C++ in 14 Days - portal

434 Day 12
Each component narrative consists of three sections:
■ A description of the component, its module, and class ancestor, as well as tables
listing its key properties, methods, and events
■ A key elements section
■ A tasks section
The key properties, methods, and events tables are by no means exhaustive—see the
C++Builder documentation, or, better yet, the VCL source code, for complete lists of these.
The idea is to give you a thorough baptism into the C++Builder database architecture without
venturing into every nook and cranny of the VCL.
TSession
Module: DB Class ancestor: Tcomponent
Because C++Builder automatically creates a TSession component for you each time your
application runs, you won’t normally need to create one yourself. This built-in TSession can
be referenced using C++Builder’s global Session variable.
As a rule, you won’t need more than one TSession per application. The only exception to this
is when you’re building multithreaded database applications. When doing that, you may
need to use TSession components to open extra connections into your server in order to keep
database access in one thread from interfering with that in another. You can drop as many
TSession components as you need onto a form or data module and then utilize them in your
Database and TDataset components. In a multithreaded database application, you typically
set up one TSession per thread. Note that C++Builder defines another global variable,
Sessions, for tracking multiple Session components in a single application. Sessions is of
type TSessionList and contains an entry for each Session component in the application.
Table 12.2 lists the key properties, Table 12.3 lists the key methods, and Table 12.4 lists the
key events for TSession.
Table 12.2. TSession key properties.
Property Description
DatabaseCount Returns a count of the number of active TDatabases.
Databases Returns the array of active TDatabases.
Handle Provides access to the BDE handle—used for direct BDE calls.
KeepConnections Determines whether inactive connects are retained.