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2. Accessing Database Files10
Chapter
Accessing Database Files
McGraw-Hill
© 2006 The McGraw-Hill Companies, Inc. All rights reserved.

3. Objectives Use database terminology correctly
Create Windows and Web projects that display database data
Display data in a DataGridView control
Bind data to text boxes and labels
Allow the user to select from a combo box or list box and display the corresponding record in data-bound controls

4. Visual Basic and Database Files
VB projects can display and update the data from database files
VB .NET uses ADO.NET for database access
ADO.NET is the next generation of database technology, based on Microsoft's previous version, ActiveX Data Objects (ADO)
An advantage of ADO.Net is that information is stored and transferred in Extensivle Markup Language (XML)
ADO.NET allows the access to database data in many formats including: OleDb, SQLClient for SQL Server (Microsoft’s proprietary DBMS), Odbc, and Oracle. Data from sources such as Access, Oracle, Sybase or DB2 can be obtained when using OleDb

5. Database Terminology Databases
Tables – can be viewed like a spreadsheet
Records (rows) – data for one item, person, transaction
Fields (columns) – stores a different element of data
Key field (unique to each record)
Relational database
Multiple tables
Relationships between the tables
To use database file the standard terminology of relational databases needs to be understood.

6. Database Table Example

7. XML Data (1 of 2)
Industry-standard format for storing and transferring data
The XML needed for accessing databases will be automatically generated in Visual Basic
Data stored in XML is text, identified by tags-similar to HTML tags and can be edited by any text editor program
Tags in XML are not predefined as they are in HTML
Tags can identify fields by name
*Specifications at World Wide Web Consortium (W3C)

8. XML Data (2 of 2)
In addition to an XML data file there is normally an XML schema file
Schema describes the fields, data types, and any constraints, such as required fields
ADO.NET validates the data against the schema and checks for constraint violations
Schema is defined with XML tags and can be viewed/edited in a text editor
ADO.NET can treat the XML data as objects-allows the IntelliSense feature of the VS.NET environment to provide information to the programmer
Data executes faster

9. Using ADO.NET and Visual Basic
Can display data from a database on
Windows Form
Web Form
Add controls to form and bind data to them
Label, TextBox
Special controls designed just for data such as DataGrid, DataList
Remember that controls for a Windows application are different from controls for a Web application and have different properties and events

10. The DataGrid View Control
The DataGridView control is bound to a table in a dataset. The data fields display automatically in the cells of the grid.

11. Data Access in Visual Studio 2005
Allows an easy way to create data-bound controls on a form
Can drag tables and fields from the window onto a form to automatically create controls that are bound to the data
Data can be displayed in grids or individual fields-referred to as details
Can drag a field from the Data Sources window and drop it on an existing control-causes data binding to be set up automatically
An .xsd file and the schema is added to the Server Explorer window; Binding Source, Table Adapter, and Data Set objects are added to the form’s component tray
To set up data access in VB several classes and objects are used

12. Overview of Database Objects
Binding Source
Establishes a link to the actual data; a specific file and/or server
Table Adapter
Handles retrieving and updating the data
Generates SQL statement that are used to access or update data
Dataset
Contains actual data, may come from multiple connections and/or multiple data adapters

13. Steps to Display Data in Bound Controls on a Form

14. Binding Sources
Object establishes a link from a specific file or database to the program
Can you a wizard to automatically create Binding Source objects –OR—
Add new Binding Source objects using the Data Sources window or the Data menu

15. Table Adapters
Does all the work of passing data back and forth between a data source (the binding source) and a program (the dataset)
Data does not have to be from a database
Data can be text file, object, or an array
Transfers data to and from via XML

16. Datasets Temporary set of data stored in memory
In ADO.NET datasets are disconnected; the copy of data kept in memory does not keep an active connection to the data source
Dataset may contain multiple tables and relationships
Any controls bound to the dataset will automatically fill with data

17. The Smart Tag Smart Tags are used for many functions including:
Selecting a data source
Editing properties of grid columns
AutoFormat the grid
Preview data
Preview helps users do a better job of designing output
Selecting AutoFormat allows the user to choose from many predefined format
*The next slide displays the grid with a predefined format

18. Grid with Pre-Defined AutoFormat
Predefined formats can be applied from the AutoFormat item on the smart tag.

19. The Database Schema File
When a new data source is added to a project, a file .xsd is added to the Solution Explorer-the XML schema definition
XML file contains the description and properties of the data
The schema shows the names of the table(s) and fields, the primary keys for each table and the relationships among the tables
At the bottom of the schema appears the TableAdapter for the table which handles different methods for the table

20. .XSD File
The .xsd file holds the schema of the database, where table elements, relationships, and keys can be viewed and modified

21. Binding Individual Data Fields
Table fields from the dataset can be bound to many types of controls such as labels, text boxes, combo boxes, and check boxes
Controls that are connected to fields are bound controls or data-bound controls
Easiest way to create bound controls is to use the automatic binding feature of the Data Source window
Creates individual text box controls for each field of data and navigation control allowing the user to more from one record to another
*The next slide displays a form with data0bound text boxes

22. Data-Bound Text Boxes -Example
Each text box or check box is bound to one field from the table. As the user clicks the
navigation buttons, all controls change to display the data for
the next record

23. The Data Sources Window
This window is used to add a new data source by using the Data Source Configuration Wizard
Click the table name to make a drop-down list available to view Details
The table’s icon changes to match the view

24. Selecting Records from a List
Allows user to select records to display from a list
Fill a ListBox or ComboBox with values from the database –OR—
Display the information in a drop-down list and allow the user to make a selection; the corresponding data elements fill remaining fields

25. Selecting Fields from the Table
Select individual fields when creating the new data source –OR– after creating the data source
When creating the data source choose the AddNewData Source option and follow the Configuration Wizard; expand the Tables node and palce a check mark on the desired fields
To modify after creating, select the dataset and use the Configuration Wizard and make the field selections from the Wizard
*The next slide displays the Data Source Configuration Wizard

26. Data Source Configuration Wizard
Select only the fields that are to be included in the Data Source Configuration Wizard

27. Sorting the List Data
Sort records in a query that selects data for the dataset
SQL SELECT statement is generated automatically by the designer; can be modified
Use the Solutions Explorer and the schema file (.xsd extension) and the Property button (…)
Choose “Ascending” in the Sort Type cell of the Query Builder
Execute the query to preview the output
You cannot sort bound data in a combo box or list box using the Sorted property of the control
*The next slide displays the dialog boxes to sort data

28. Sorting Data
Click the Fill,GetData() entry in the dataset schema to display the properties of the Fill command in the Properties window.
Select Ascending for the Sort Type to sort the data by the Title field. The SQL statement changes to include an ORDER BY clause

29. Choosing the Control Type for Fields
Dragging a Details view to a form displays text boxes for the default text fields
Click a field name and choose a control type in the Data Sources window
You can choose the control type for all controls and then drag the table to the form to create the Details view

30. Selecting Records Using Web Forms
Web controls are much different from Windows controls
Additional security issues for Web-based database applications
Web database applications operate differently than Windows applications due to web pages in a client/server environment
Web pages are stateless—each time a page displays it is a new page
Each time the user makes a selection from a list a postback occurs and the Web page redisplays with only the selected data
When you write database programs for the Web instead of Windows, you have a few more considerations—setting up data sources and bind to controls—but the Web controls are considerably different from their Windows counterpart

31. Security in Web Database Applications
Security is much tighter for Web database applications than for Windows applications
Require user authentication if setting up a Web application that displays or allows modification to data
Visual Studio 2005 integrates security features which are general strict by default
Visual Studio 2005 ensures that data will be secure unless the user takes steps to unprotect the files

32. Moving Database Projects
Improvement from previous versions of VB.NET
Project needs to be closed in the IDE
Copy the complete folder from one computer or location to another
For Web projects, open the IDE, select Open Web Site and browse to the folder
You should be able to move the database projects in this chapter to another
computer, open them in the IDE, and edit and/or run the applications. This is a huge improvement over earlier versions of VB .NET.