1. Using Visual Basic 6.0 to Create Web-Based Database Applications
Chapter Six
Using Visual Basic 6.0 to Create Web-Based Database Applications

2. Chapter Objectives
Learn about the Visual Basic development environment
Learn about the components of a Visual Basic database application
Create a Visual Basic application using the ADO data control to display database data

3. Chapter Objectives
Create programmatic data controls to process data in a Visual Basic program
Create a Visual Basic ActiveX document that is run from a Web page

4. Figure 6-1: Installing an ActiveX document
ActiveX Documents
ActiveX documents
A program that users can download from a Web site and install on their computers
Figure 6-1: Installing an ActiveX document

5. Overview of Visual Basic
Can be used to create almost any kind of Windows-based program
An event-driven programming language
Program statements execute in response to user actions or to system actions

6. Components of a Visual Basic Program
Project file
Specifies properties of the program and the names of the individual component of the program
Form
Main components of a VB project
Composed of the visible interface that the user sees and interacts with, and the associated code that responds to user and system actions

7. Components of a Visual Basic Program
Standard module
Contains only code
Used to store declarations for variables that are used in multiple forms
Procedure
Manipulates variable values
Function
Returns a single value based on parameters that are passed to the function

8. Components of a Visual Basic Program
Controls are the visible items on a form
Figure 6-2: Form Controls

9. Visual Basic Projects
When VB is started, a new project is created, which corresponds to an individual user application
When you create a new project, you can select the type of project it will be, which specifies how the project file is compiled

10. Visual Basic Projects
Figure 6-3: Visual Basic project types

11. The Visual Basic Development Environment
Integrated development environment (IDE)
Environment for developing programs
Figure 6-4: VB IDE components

12. The Visual Basic Development Environment
Main IDE components include:
The toolbar provides quick access to menu bar commands for opening
The Object window shows the form and the position of the controls on the form
The toolbox contains icons that are used to create form controls

13. The Visual Basic Development Environment
Main IDE components include (cont.)
The Project Explorer displays a hierarchical list of the components of the current project
The Properties window is used to assign and display the properties of the object that is currently selected in the Form window
Docking
Allows the borders of windows to be attached, or docked, to other windows

14. Creating a Visual Basic Database Application
Data control
Form control that is attached to a database table
Used to sequentially step through the record to view the items

15. Creating a Visual Basic Database Application
Figure 6-8: Clearwater Traders Inventory Maintenance application

16. Modifying Form Properties
The properties of a VB object specify the object’s appearance and behavior
Name property
Determines how objects are internally identified within the project
Must begin with a letter and can contain characters, numbers, or underscores

17. Modifying Form Properties
Table 6-1: VB object name prefixes

18. Modifying Form Properties
To follow accepted Windows application design guidelines, you should always modify the following form properties:
Border Style, which determines whether the user can resize the form
Caption,which is the form description that is displayed in the form’s title bar
MaxButton, which allows the user to maximize the form so that it is displayed full-screen

19. Modifying Form Properties
To follow accepted Windows application design guidelines, you should always modify the following form properties (cont.):
MinButton, which allows the user to minimize the form
StartUpPosition, which determines where the form is displayed on the screen when the application is running

20. Saving Visual Basic Projects
A VB project is saved in a file with a .vbp extension
Forms are saved in files with an .frm extension
When you create a new project, it is very important to always save the project (.vbp) file and the form (.frm) file in the same folder in your file system

21. Using Visual Basic with a Database
ODBC driver
Low-level program that translates messages from an application into the syntax expected by a specific database
Each different type a database requires a different ODBC driver
Always runs on the client workstation

22. Using Visual Basic with a Database
Programs written in program development languages and applications that access databases, need to communicate with ODBC drivers
To simplify this communication, Microsoft has developed a variety of different data access technologies: Data Access Objects (DAO), Remote Data Objects (RDO), and ActiveX Data Objects (ADO)

23. Using Visual Basic with a Database
DAO
Available in most applications that support database connectivity, but cannot support action queries that change content in some databases
RDO
Full-featured, but only available in Microsoft’s high-end enterprise-level programming environments
ADO
Full-featured, is available in most Microsoft environments, and supports most types of queries

24. Using Visual Basic with a Database
Figure 6-12: Microsoft data access architecture using ODBC

25. Using Visual Basic with a Database
Figure 6-13: Microsoft data access architecture using ADO and OLE DB

26. Creating an ActiveX Data Control
A control that is displayed on a form
Different from an ordinary form control because it is associated with a recordset
A specific set of database records based on a SQL query

27. Creating an ActiveX Data Control
Figure 6-14: ActiveX data control

28. Creating an ActiveX Data Control
To create an ADO data control, you must add a type library to your project
A type library is a library of code that has programs, such as additional controls, that you can add to VB IDE and then use in your project

29. Using Program Code to Process Data
With a programmatic data connection:
All of the commands to create the connections and execute SQL commands are specified in a VB standard module
User does not have to interact with a visible data control to perform database operations

30. Variables in Visual Basic Programs
Visual Basic code has variables and data types just like other programming languages
It is a good programming practice to always declare variables before using them
VB does not require you to declare variables, but allows you to assign a value to a variable without declaring it first. This can lead to errors
StudentAge = 22
StudentAge = StdentAge + 1
Option Explicit

31. Variables in Visual Basic Programs
Declaration keyword that is used to declare a variable depends on the desired scope of the variable
Scope
Specifies how long the variable exists in memory
Specifies what program components can assign and access the variable value
Public, Private, Dim, Static

32. Variables in Visual Basic Programs
Variable declaration keywords are used as follows:
The Public keyword is used to declare global variables
These are variables that are visible to all forms and modules within a project

33. Variables in Visual Basic Programs
Variable declaration keywords are used as follows (cont.):
The Private keyword is used to declare form-level and standard module-level variables
These are variables that are visible only to procedures and functions written within the form or standard module where the variable is declared

34. Variables in Visual Basic Programs
Variable declaration keywords are used as follows (cont.):
The Dim keyword is used to declare local variables
These are variables that are visible in the function or procedure where they are declared

35. Variables in Visual Basic Programs
Variable declaration keywords are used as follows (cont.):
The Static keyword is used to declare local variables whose values are only visible within the procedure where they are declared, but whose values still exist and can be accessed after the procedure is exited

36. Variables in Visual Basic Programs
The Variant data type can store any type of data
Table 6-2: Visual Basic data types

37. Visual Basic Objects and Collections
In object-oriented programming languages, an object is an item that has a specific structure and behavior (forms, controls)
Methods (objects have associated methods)
Procedures that perform an operation on an object
Collection (forms collection contains all forms in a VB application)
Contains a set of related objects

38. Running Programs in the Visual Basic IDE
Source code
The program code that you write
Interpreted
Means that the code is translated to machine language and executed one line at a time
Compiled
Means that all of the code is translated into machine language, and the machine-language version is then stored as an executable file

39. Message Boxes
A message box provides information to user regarding status of program or current operation
Figure 6-23: Message box

40. Using a DataGrid Control
Figure 6-29: Inventory form

41. Displaying Visual Basic Programs Using Web Pages
Visual Basic projects can be created to make standard executable files
Also can be created using different ActiveX options to make programs that can be installed and/or run by clicking a hyperlink on a Web page

42. ActiveX Options Supported by Visual Basic
Active documents
Have both a visual interface and code to process user inputs and actions
Active programs
Provide processing for other Web programs, but do not have a visual interface component
Active controls
Used to create custom controls that can be used in other Web-based programming projects

43. Creating an ActiveX Document
User document
Container object in an ActiveX document
Similar to a form in the sense that it can contain controls and code, and has events similar to those in a form
A user document must be associated with, or sited on, an external application, which is called a container

44. Displaying an ActiveX Document using a Hyperlink
When creating a Internet package using Package and Development Wizard, the Wizard creates an HTML file containing the command for the hyperlink that references the ActiveX document
Figure 6-34: Link to ActiveX document file in HTML file created by Package and Development Wizard