Chapter 3. An Explanation of the Tutorial Code

A DataHub script defines an object called an Application object. This object is a class derived from the class Application. All of the functions that you define should be methods of this class. Variables should be members of this class wherever possible.

class MyODBCScript Application
{
  env;    // store the ODBC environment here
  conn;   // store the ODBC connection here
}

This defines the application object.

The application object requires a constructor. The constructor acts as the main line of your program. To start your program, you just create an instance of the application class, causing the constructor to run.

method MyODBCScript.constructor ()
{
  // This is the program main line
}

The job of the constructor is to define event handlers. An event handler is program code attached to a particular event. An event can be one of:

The constructor runs to completion. Once the constructor completes, the script engine begins processing events, and executes the program code attached to those events.

The script engine will continue to process events until the application object is destroyed. You may optionally provide a destructor for the object to clean up any specific data or open any files or timers that your application has created.

method MyODBCScript.destructor ()
{
  // This is where you clean up open files and connections
}

You can add other methods to the application object as you need them. Only the constructor is necessary.