1. Copyright Scott-Jones Publishing, 2004-2005. All rights reserved.
3: ADO.NET Databases
Updated 9/5/2004
Copyright Scott-Jones Publishing, All rights reserved.

2. Overview Introduction to ADO.NET Using Data-Bound Controls
Navigating, Adding, and Removing Rows
Selecting DataTable Rows
Advanced Visual Basic .NET (Irvine, Liang, Gaddis) Slide 2

3. 3.1 Introduction to ADO.NET
Provides access to database data sources
Microsoft SQL Server
Microsoft Access
databases that support OLE DB and XML (many do this)
ADO designed for client-server model
ADO.NET designed for internet applications
A more loose connection between web client and server
Supports XML, an internet data transmission standard
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4. Two ADO.NET Modes ADO.NET supports a connected and disconnected mode
database connection kept open while reading all data
rows can only be accessed in forward direction
read-only access to data
Disconnected
entire database table copied into memory
connection closed
program works with the in-memory copy called a dataset
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5. Reading From a Database
We use disconnected mode in Chapter 3
VB.NET uses 3 related classes
a database connection object defines access to the DB
a data adapter object transfers data from DB to dataset
a dataset object is used as the data container
Visual Studio used to create and configure these objects
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6. Database Basics
Database – collection of one or more tables, each containing data related to a particular topic
Table – logical grouping of related information
Departments table example:
Each row can be called a record
Each column can be called a field
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7. Primary Key
Primary key consists of one or more columns that uniquely identify each table row
Required when performing table updates
Example: dept_id is the primary key
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8. Clustered Primary Key Product Sales table example
no column contains unique values
we can combine date, product_id, and customer_id columns to form a composite key
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9. Designing Database Tables
Database schema
design of tables, columns, and relationships between tables
Principles
avoid duplication of data
create separate tables linked by a common column
Database relationships
one to one
one to many
many to many
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10. One to Many Relationship
Departments and Employee tables, linked by dept_id
Employee table contains integer dept_id
Table relationships will be explored more fully in Chapter 5.
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11. Microsoft Access Data Types
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12. Data Sources and Connections
ADO.NET data flow
Only one connection object needed for the database
One connection can support multiple data adapters
Each data adapter has a related dataset that it fills
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13. Data Providers OLE DB .NET Data Provider SQL Server .NET Data Provider
general use
use for most databases, including Access
SQL Server .NET Data Provider
Used specifically for SQL Server databases
faster than OLE DB
Chapters 3 and 4
Chapter 5 onward
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14. ADO.NET Connection Classes
OleDbConnection
connects to any OLE DB database
minimal connection string
two basic parameters:
Provider=Microsoft.Jet.OLEDB.4.0; _
Data Source=SalesStaff.mdb
SqlConection
connects to SQL Server database
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15. Database Connections Connection properties may be hard coded
Or connection properties below may be set in code
Connection has Open() and Close() methods
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16. Data Adapter OleDbDataAdapter and SqlDataAdapter Actions:
components in Visual Studio Toolbox
Actions:
reads data from data source into a dataset
writes data from dataset to a data source
Retrieves data by executing an SQL query
Three ways to construct the SQL query:
entered in Visual Studio thru the data adapter configuration
in program code using SelectCommand property
in a compiled stored procedure
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17. Visual Studio Toolbox
Wizards are provided for both OLE DB and SQL Server configuration under the Data tab in the toolbox
MS-Access
SQL Server
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18. Datasets
In-memory cache of records holding table data retrieved from one or more data sources (data adapters)
Disconnected from data source
updates are initially written to the dataset
Underlying database changed only by a call to the data adapter's Update method
Update method writes dataset changes to the database
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19. DataSet Class System.Data namespace Important properties
Tables: lists DataTable objects used to create dataset
Dim tbl as DataTable
For Each tbl in DsSalesStaff1.Tables
List1.Items.Add(tbl.TableName)
Next
PrimaryKey: lists columns that make up the primary key
tbl = dsSalesStaff1.SalesStaff
Dim index as Integer
For index = 0 to tbl.PrimaryKey.Length – 1
List1.Items.Add(tbl.PrimaryKey(index))
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20. Other Classes DataRow DataColumn holds a single row in a DataTable
has properties corresponding to database columns
For index = 0 to tbl.Rows.Count – 1
ListBox1.Items.Add(tbl.Rows(index).Item(0))
Next
DataColumn
describes a single column in a DataTable
For index = 0 to tbl.Columns.Count -1
ListBox1.Items.Add(tbl.Columns(index))
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21. 3.2 Using Data-Bound Controls
Data binding
permits controls to display and update dataset columns
Data-aware control
can bind itself to a dataset column
DataBindings.Text property is assigned a column name
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22. SalesStaff 1 Hands-on tutorial
Shows how to set up a database connection
Uses data-bound controls
Displays a single row of the SalesStaff table
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23. Structured Query Language (SQL)
Universal language for retrieving data and manipulating databases
Two varieties in Visual Basic .NET:
Jet SQL (MS-Access)
ANSI SQL (SQL Server)
Most common statement: SELECT
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24. SQL SELECT Statement SalesStaff example
FirstName, HireDate, IsFullTime, LastName,
Salary, StaffId
FROM
SalesStaff
Create alias for any column name
FirstName, LastName, Salary,
HireDate AS DateHired
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25. SQL – Setting Row Order ORDER BY statement
Identify columns on which to sort
Specify ASC or DESC direction
Examples:
ORDER BY LastName
ORDER BY Salary ASC, HireDate DESC
ASC is the default direction
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26. 3.3 Navigating, Adding, and Removing Rows
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27. CurrencyManager Object
Navigates between rows of a dataset bound to a form
Properties:
Count, integer with number of rows in the dataset
Current, a DataRowView object that returns the current row
Position, integer with current dataset row from 0 to count - 1
Methods:
Refresh resets bound controls to values in dataset
CancelCurrentEdit rejects changes to the current row
EndCurrentEdit accepts changes to the current row
RemoveAt deletes the row specified
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28. CurrencyManager Object
The WithEvents keyword allows your code to respond to CurrencyManager events such as .PositionChanged
Obtained from the form's BindingContext:
Private WithEvents currManager As CurrencyManager
currManager = Me.BindingContext(dsSalesStaff1, _
"SalesStaff")
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29. Moving Between Rows
Add or subtract an integer from the form's CurrencyManager object
Examples:
move down one row:
currManager.Position += 1
move up one row:
currManager.Position -= 1
move to last row:
currManager.Position = currManager.Count - 1
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30. Adding a New Row
NewRow method creates a row having same structure as the existing dataset
The process of adding a new row:
First, create empty row in dataset for the SalesStaff table
Dim newRow As System.Data.DataRow
newRow = DsSalesStaff1.SalesStaffRow.newRow()
Second, fill the columns with values
newRow.StaffId = "104"
newRow.FirstName = "Andrew"
newRow.LastName = "Chang"
OR... addForm.newRow = newRow (if controls are bound)
Finally, add the new row to the table's Rows collection
DsSalesStaff1.SalesStaff.Rows.Add(newRow)
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31. Catching Exceptions
Errors can occur when adding a new row to a dataset
ConstraintException thrown if duplicate key value
CancelEdit method used to reject the add attempt if an exception is thrown
Try
newRow.StaffId = "104"
newRow.FirstName = "Andrew"
newRow.LastName = "Chang"
'(assign other column values . . .)
dsSalesStaff1.SalesStaff.Rows.Add(newRow)
Catch except As Exception
MessageBox.Show(except.Message)
newRow.CancelEdit()
End Try
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32. Common Operations Remove a Table Row:
method 1: Use CurrencyManager.RemoveAt method
currManager.RemoveAt(currManager.rowNbr)
method 2: Use DataTable.Rows.Remove method
dsSalesStaff1.SalesStaff.Rows.Remove(rowNbr)
Update the Database with changes in the Dataset
general form:
DataAdapter.Update( DataSet )
example:
daSalesStaff.Update(DsSalesStaff1)
Reload the dataset
daSalesStaff.Fill(DsSalesStaff1)
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33. Checking for Null Values
DataRow columns contain null if they have not been initialized
Example: DbNull.Value checks for null LastName in the first row of table SalesStaff in dataset DsSalesStaff1:
Dim row As DataRow = DsSalesStaff1.SalesStaff(0)
If row("LastName") Is DbNull.Value Then
'LastName is null
End If
(see page 196)
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34. Updating the SalesStaff Table
SalesStaff 2 example
Adds, removes, and updates dataset rows
Updates the underlying database
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35. Column Names as DataTable Properties
The specific DataTable class contains a property for every database table column
SalesStaff example
Both statements below retrieve the contents of the Salary column from row 0 of the SalesStaff table:
DsSalesStaff1.SalesStaff.Rows(0).Item(“Salary”)
DsSalesStaff1.SalesStaff(0).Salary
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36. Query Builder
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37. Opening the Query Builder Tool
Select data adapter object, view properties
Expand SelectCommand
Click on SelectCommand CommandText property
Click on ellipsis button
Query Builder window opens
Provides a QBE interface to create SQL queries
Change SalesStaff3 program to list by first name
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38. SalesStaff 3 Hands-on example iterates through a dataset table
displays names in a list box
With DsSalesStaff1
Dim i As Integer
For i = 0 To .SalesStaff.Count - 1
namesForm.lstNames.Items.Add( _
.SalesStaff(i).LastName & ", " & _
.SalesStaff(i).FirstName)
Next
End With
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39. SalesStaff 3 Alternative code to insert names in list box
For-Each loop with specific DataRow type:
With DsSalesStaff1
Dim row As dsSalesStaff.SalesStaffRow
For Each row In .SalesStaff.Rows
namesForm.lstNames.Items.Add( _
row.LastName & ", " & _
row.FirstName)
Next
End With
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40. Filling List and Combo Boxes
Design mode:
assign dataset name to the DataSource property
asssign column name to the DisplayMember property
At runtime:
fill the dataset object from the data adapter
SelectedIndexChanged event
fires when list box or combo box is filled from the dataset
use special logic to prevent program from reacting before the user has made a selection
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41. ValueMember Property ListBox and ComboBox
References a table column that will be a lookup value
At run time, get the SelectedValue property
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42. 3.4 Selecting DataTable Rows
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43. SQL WHERE Clause Filters or selects rows from a dataset table
String literals are surrounded by single quotes
Date literals
MS-Access: surround with #...#
SQL Server: surround with single quotes
Examples:
WHERE LastName = 'Gomez'
WHERE Salary > 30000
WHERE LastName >= 'B'
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44. SQL WHERE Clause LIKE and BETWEEN: All values beginning with letter A:
WHERE LastName LIKE 'A%'
All values beginning with 1 and ending with 4:
WHERE StaffId LIKE '1_4'
All values within a range:
WHERE (HireDate BETWEEN #1/1/1992# AND #12/31/1999#)
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45. Selecting Karate School Members
Hands-on tutorial
Karate database, Members table
User selects a name from a combo box
Program fills in remaining form fields from the dataset
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46. Parameterized Queries
Values in a WHERE clause can be provided at runtime
Adds much flexibility to a static query
Access and SQL Server work slightly differently:
MS-Access, values provided at runtime identified by a ?
SQL Server, values provided at runtime begin
next: examples
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47. Parameterized Queries Using Access
SQL contains ? for value to be provided:
SELECT BirthDate, City, FirstName, LastName,
MemberId, Phone, Street, Zip
FROM Members
WHERE (LastName = ?)
VB sets the following data adapter property
daMembers.SelectCommand.Parameters("LastName").Value = txtLastName.Text
Alternative method uses an index instead of a name
daMembers.SelectCommand.Parameters(0).Value
= txtLastName.Text
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48. Parameterized Queries using SQL Server
SQL for value to be provided:
SELECT BirthDate, City, FirstName, LastName,
MemberId, Phone, Street, Zip
FROM Members
WHERE (LastName
VB sets the following data adapter property
= txtLastName.Text
Alternative method uses an index instead of a name
daMembers.SelectCommand.Parameters(0).Value _
= txtLastName.Text
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49. Assigning Parameter Values
Identify parameter by name or index position
MS-Access:
daMembers.SelectCommand.Parameters("LastName").Value _ = txtLastName.Text
daMembers.SelectCommand.Parameters(0).Value _
= txtLastName.Text
SQL Server:
_ = txtLastName.Text
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50. Creating an SQL Statement in Code
Ultimate flexibility obtained by assigning the SQL in code
Set data adapter SelectCommand.CommandText property
An SQL query selecting a user entered customer name
daSalesStaff.SelectCommand.CommandText =
"SELECT FirstName, LastName FROM SalesStaff " &
"WHERE LastName = '" & txtLastName.text & "';"
Note the value provided by txtLastName.text must be enclosed in single quotes per standard SQL syntax
Numeric fields do not require single quotes
Date example:
"WHERE HireDate = #" & txtHireDate.text & "#;"
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51. The End
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