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Chapter 10
Accessing
Database Files
Programming In
Visual Basic.NET
Visual Basic and Databases
• 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)
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
ADO.NET
• Data is stored and transferred in Extensible
Markup Language (XML)
• Allows access to database data in many
formats
• Two types of Connections
– SQLClient for SQL Server
– OLEDB for all other database formats
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Relational Database Terminology
• Database includes
– Tables => collection of related data
– Queries => SQL designed to select data from tables
• Table
– Record => row of related data for one instance
– Field => column of specific data element
– Keys
• Primary => uniquely identifies a record
• Foreign => links record to related record in related
table
• Relationships
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Using ADO.NET and VB
• Can display data from a database on
– Windows Form
– Web Form
• Add controls to form and bind data to them
– Normal Controls like label, textbox
– Special controls designed just for data like
DataGrid, DataList
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Steps for Data Access
Data
Source
Specific
file
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Connection
OleDbConnection
Object
Data
Adapter
Handles data
transfer and
provides data
for dataset;
uses SQL
Web
Form
Dataset
Windows
Form
Actual data,
can contain
multiple
tables
Bound
controls
display
data
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Connection
• Used to establish link form specific file or
database to program
• Types
– SqlConnection
• Microsoft SQL Server databases only
– OleDBConnection
• All other databases
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Setting Up a Connection
• Can be accomplished from
– Toolbox
– Server Explorer window
– Within Data Adapter Configuration Wizard
using New Connection button
• No matter which method above is used to
begin the connection, the Data Link
Properties dialog appears for you to
complete the task
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Creating a Connection from
Server Explorer
• Click Connect to
Database button
OR
• Right-click Data
Connections
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Data Link Properties Dialog
• Used to define
Connection's
– OLE DB Provider
– Actual DB Filename
– Logon UserName and
Password (optional)
• Used to Test
Connection
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Connections in Server
Explorer
• Shows all created
Connections
• Same Connection
can be use for
multiple projects
• Expand Connection
node to view tables
and fields
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Data Adapter
• Does all the work of passing data back and
for the between a data source and a program
• Does not have to be a database
• Can be text file, object, or even an array
• Types, must match Connection type
– OleDbDataAdapter
– SqlDataAdapter
• Use db prefix (e.g. dbRnR)
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Setting Up a Data Adapter
from Server Explorer
• Drag Table name
to form
OR
• CTRL-click Field
names and drag to
form
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Data Adapter Configuration
Wizard
• Walks you through the steps for selecting
fields in a database
• Only used if you create/add a Data Adapter
from the Toolbox
• Can be used to modify existing Data
Adapters also
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Dataset
• 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
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Defining a Dataset
• Drag Dataset control from
the toolbox to
form
• Select Data menu, Generate
Dataset
• Right-click on Data Adapter
and select Generate Dataset
• In all cases, you see the
Generate Dataset dialog box
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Defining a Dataset (cont.)
• Name dataset with
ds prefix in
Generate Dataset
dialog (e.g.
dsBooks)
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Data Passing from Data Source
to Dataset to User Interface
Presentation Tier
Windows
Forms
Dataset
Business Tier
Data Tier
Data Object
(Class)
XML
Dataset
XML
Web
Forms
Dataset
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Data
Source
XML
XML
Data
Adapter
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
XML Data
• Industry-standard format for storing and
transferring data
• Specifications at http://www.w3.org/XML,
World Wide Web Consortium (W3C)
• The needed XML for accessing databases
will be automatically generated for you in
Visual Basic
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XML
• Data stored in XML is all text
• XML Data File
– Contains actual data
• XML Schema File
– Contains descriptions for
• Fields
• Data Types
• Constraints, such as required fields
– .xsd file in Solution Explorer
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Fill Method
• Method of the Data Adapter executed at run
time to fill the dataset
• Usually coded in Form_Load (or
Page_Load for Web Projects)
• General Form
DataAdapterName.Fill (DataSetName)
• Example
dbRnR. Fill (dsBooks1)
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Creating Bound Controls: Data Grid
• In Windows Form
– Set properties of the controls
– Use Fill method
• Example: Grid Control
– New control in VB.NET
– Displays database records as a table
• Steps
– Set up/add Connection, DataAdapter, DataSet
– Add DataGrid control from toolbox (dbg
prefix)
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Creating Bound DataGrid
• Steps continued
– Set properties of DataGrid to bind to data
• DataSource to DataSet name
• DataMember to Table name
– Add code to populate control with data
• Windows Form, Form_Load ==>
DataAdapterName.Fill (DataSetName)
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Creating Simple Bound Controls
• Labels and text boxes
• Same steps:
– Set up/add Connection, DataAdapter, DataSet
– Add text boxes or label control from toolbox
– Set properties to bind to data
• Data Binding properties menu
• Text option to be specified
– Add code to populate control with data
• Windows Form, Form_Load ==>
DataAdapterName.Fill (DataSetName)
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Navigating Through DataSets
• Refer to the Position and Count properties
of the Windows Form's BindingContext
' Move to next record
Me.BindingContext(dsBooks1, "Books").Position + = 1
' Move to previous record
Me.BindingContext(dsBooks1, "Books").Position - = 1
' Move to the first record
Me.BindingContext(dsBooks1, "Books").Position = 0
' Move to the last record
With Me.BindingContext(DsCustomer1, "Customer")
.Position = .Count - 1
End With
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Retrieving Record Count
• Specify
–
–
–
–
DataSet
Table Name
Rows Collection
Count Property
• Example
intRecordCount=dsBooks1.Tables("Books").Rows.Count
‘Ulternatively
Me.BindingContext(DsCustomer1, "Customer").Count
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Updating a Database File
• Types of updating
– Modify existing records
– Add records
– Delete records
• Must display the dataset in bound controls
that can be used for input (no labels)
• You must write code to actually update the
database
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Typical Form for Updating
Add caption
changes to
Cancel during
Add or Edit
All Navigation Buttons
are disabled during Add
or Edit
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Save Button is
enabled only
when an Add
or Edit is in
progress
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Update Method
• Method of DataAdapter used to write
changes to database
‘General Form
DataAdapterName.Update (DataSet, "Table")
‘Example
dbRnR. Update (dsBooks1, "Books")
• Can be executed
– After every change, perform data validation,
then execute Update (Save Record button)
– Once, just before program termination for all
changes execute Update (Form's Closing event)
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Update Method (cont.)
• Automatically loops through the records in a table
to determine what type of update is needed and
then performs the required SQL
– Update
– Insert
– Delete
• Execute during Form's Closing event if running
once to apply all changes
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Example - Update Form's
Closing Event
' mblnIsDirty was declared in Declarations section
'Save changes, Update Database
If mblnIsDirty Then
If MessageBox.Show("Save Changes?", "Books" _
MessageBoxButtons.YesNo, _
MessageBoxIcon.Question ) = DialogResult.Yes Then
Try
dbRnR.Update(dsBooks1, "Books")
Catch
MessageBox.Show("Error saving file", "Books")
End If
End If
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Logic of Update Programs
• Enclose all statements that access the
database in Try/Catch blocks
• Display data in bound input controls
– Initially set ReadOnly property = True
• When user clicks Edit button
– Set ReadOnly = False
– Disable Navigation buttons
– Provide Cancel and Save buttons for user
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Saving Changes Logic - User
Clicks Save Button
• Perform Data Validation
– If valid data then
•
•
•
•
Set ReadOnly = True
Set mblnDirty = True
Enable Navigation buttons
Disable Save button
– If invalid data then
• Notify user with MessageBox
• Set focus to control containing invalid data
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Canceling Changes Logic User Click Cancel Button
• Replace changed values in controls with
original values
–
–
–
–
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See RejectChanges procedure (p 441)
Set ReadOnly = True
Enable Navigation buttons
Disable Save button
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Deleting Records
• Execute Delete Method of the table's Rows
collection
• Example
Dim intCurrRecNum As Integer
intCurrRecNum = Me.BindingContext(dsBooks1, _
"Books").Position
dsBooks1.Books.Rows(intCurrRecNum).Delete ( )
mblnIsDirty = True
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Adding Records
• If user clicks Add button
–
–
–
–
–
Clear bound input controls
Set ReadOnly = False
Set mblnAdding = True
Disable Navigation buttons
Provide Cancel and Save buttons for user
• Logic for Save and Cancel are same as on
previous slide except for resetting
mblnAdding to False
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Example - Saving an Added
Record
Dim newRow As DataRow = dsBooks1.Books.NewRow
newRow("Author") = txtAuthor.Text
newRow("ISBN") = txtISBN.Text
newRow("Title") = txtTitle.Text
dsBooks1.Books.Row.Add(newRow)
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Logic for Save Button
• Must determine type of operation in
progress since used for saving changes
made as
– Edits
– Adds
• Use mblnAdding variable to identify Add
operations in progress
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Bound Combo Boxes
• Provides an easy user interface for selecting
records to view or update
• Windows Forms
– Use ListBox or ComboBox
• Web Forms
– Use ListBox or DropDownList
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Using Multiple Data Adapters
• Use when more than 1 dataset or more than
1 table in a dataset is needed
• A single Connection object can supply the
connection for more than 1 data adapter
• Useful when a list is available for the user
to select the record(s) to display
– 1 dataset for the list itself
– 1 dataset for the selected record(s)
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Parameterized Query
• DataSet with special type of SQL SELECT
statement
– WHERE clause is incomplete until user enters
value for criteria at run time
– Uses question mark in place of criteria
• Example
SELECT Title, Author, ISBN FROM books WHERE Title = ?
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Filling a List - Windows Forms
• Set ListBox or ComboBox Properties
– DataSource to DataSet name
– DisplayMember to table name.field name
• Use Fill method to populate list with data
Tip: To eliminate duplicate entries in the list.
Modify the SQL SELECT statement to
include the DISTINCT keyword.
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Displaying the Data for the
Selected Item
• At run time the user may enter the value to
be used in the Parameterized Query in
– TextBox
• Include an associated button for the user to click to
use the value
• Be sure to check for possible empty dataset if the
user enters a value not in the dataset
– Selection of a ListBox or ComboBox
• Write code in the SelectedIndexChanged Event
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Example
• Combo box SelectedInexChange Event
' Get record to match selected title in list
dsBooks1.Clear( )
dbRnR.SelectCommand.Parameters("Title").Value =cboTitles.Text
dbRnR.Fill(dsBooks1)
• TextBox, Associated Button's Click Event
' Get record to match selected title in list
dsBooks1.Clear( )
dbRnR.SelectCommand.Parameters("Title").Value = txtTitles.Text
dbRnR.Fill(dsBooks1)
If dsBooks1.Tables("Books").Rows.Count = 0 Then
MessageBox.Show("Title not found.")
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Making Database Projects
Portable
• Connection information is directly tied to
database file location
• You must move database AND
– Create Connection on new computer
– Configure DataAdapter
– For Web Projects, also create Virtual Directory
• Less problems if you store the database in
the same folder as your project
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Command Summary
' Data Adapter fills a Dataset.
dbRnR. Fill (dsBooks1)
' Move to next, pervious, first and last record
Me.BindingContext(dsBooks1, "Books").Position [+ = 1, -=1, 0, .Count –1]
‘Retrieving record count
intRecordCount=dsBooks1.Tables("Books").Rows.Count
' Get record to match selected title in list
dbRnR.SelectCommand.Parameters("Title").Value =cboTitles.Text
' Save the changes in the file
dbRnR. Update (dsBooks1, "Books")
‘Add a new record
Dim newRow as DataRow = DsCustomer1.Customer.NewRow
dsBooks1.Books.Row.Add(newRow)
' Delete current record
dsBooks1.Books.Rows(intCurrRecNum).Delete ( )
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© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.