Programming Guide - Actian

Using an Object-oriented Approach to Programming ............................................................... 120Inheritance....................................................................................................................... 121Class Relationships....................................................................................................... 122User Class Hierarchies .................................................................................................. 123How Polymorphism Works ............................................................................................. 125How You Can Build an Inheritance Tree........................................................................... 126How Invoking User Class Methods in 4GL Works .............................................................. 127How You Can Create a User Class ........................................................................................ 127How You Can Encapsulate Attributes and Methods ............................................................ 128How You Can Write Methods.......................................................................................... 129How You Can Use Polymorphism .................................................................................... 130Examples of Method: Hire Method .................................................................................. 131External Classes................................................................................................................ 135ActiveX Support........................................................................................................... 135How You Can Use External Classes ................................................................................. 136Dynamic Programming with External Objects ................................................................... 136Non-Formfield External Objects...................................................................................... 136How You Can Use Collections with External Classes........................................................... 136Example—ActiveX Controls............................................................................................ 138How You Can Create Fields from User Classes........................................................................ 139How You Can Manipulate Objects Generically: Casting ............................................................ 139How You Can Work with Attributes ................................................................................. 140How You Can Work with Methods ................................................................................... 141Overview of the OpenROAD System Classes .......................................................................... 142Object........................................................................................................................ 142Class.......................................................................................................................... 143User Class Source Definition .......................................................................................... 143User Class Runtime Definition ........................................................................................ 143Source Definitions for Applications and Their Components.................................................. 144Running Applications and Their Components .................................................................... 144Field and Menu Information ........................................................................................... 145Event Information........................................................................................................ 146Chapter 6: Working with a Database 147Conceptual Background...................................................................................................... 147How You Can Access a Database with Standard SQL Statements .............................................. 148Select Statement ......................................................................................................... 149Errors Originating in Called 3GL Procedures ..................................................................... 151How You Can Use the Insert Statement........................................................................... 152How You Can Use the Update Statement ......................................................................... 153How You Can Use the Delete Statement .......................................................................... 154How You Can Use Other SQL Statements......................................................................... 154Contents v