Transcript Visual Basic Database Access

VB .NET Database Tools
ISYS 573
Microsoft Universal Data Access
• ODBC: Open Database Connectivity
– A driver manager
– Used for relational databases
• OLE DB: The OLE database protocol
– Allows a program to access information in any type of
data source.
– Data provider: databases, spreadsheets, etc.
• ADO.NET:
– An Interface for OLE DB.
– Allow programmers to use a standard set of objects to
refer to any OLE DB data source.
VB Program
ADO.NET
OLE DB
Provider
OLE DB
Provider
ODBC
Data Source
ODBC
Data Source
Steps to Retrieve Data
• Establishes a connection to the database.
• Executes commands against the database.
• Store data results.
ADO.NET Objects
.NET Applications
Data Set
Data Reader
Command Object
Connection Object
Managed Data Provider
(OLEDB)
Database
Connection Object
• Represent a connection to the database.
Command Object
• The command object allows us to execute a
SQL statement or a stored procedure.
• Basic Methods:
– ExecuteReader: Execute SQL Select statements
to create a DataReader object that contains the
results of the query.
– ExecuteNonQuery: Execute SQL’s INSERT,
DELETE, UPDATE statements.
DataReader Object
• It is a read-only and forward-only pointer
into a table to retrieve records.
• Basic Methods:
– Read: Reads the current record and advances
the pointer to the next record.
– Close: Closes the dataReader.
DataSet Object
• A DataSet object can hold several tables and
relationships between tables.
• A DataSet is a set of disconnedted data.
Data is extracted from the database and
stored in the DataSet object. Updates to the
DataSet must copy back to the database to
make the changes permanent.
VB.NET Database Tools
• Database connection:
– Tool/Connect to database
• Provider:MS Jet 4.0 OLE DB Provider
• Connection
• Server Explorer
– Data connections:
• Right click and Add Connection
• Tables, Views
• Toolbox Data tab
• Data Form Wizard
Data Form Wizard
• Creating a form with data-bound controls to
display and update information in a dataset.
• Demo: Using Data Form Wizard to create a
navigational form.
–
–
–
–
Project/Add Windows Form/Data Form Wizard
Set connection
Choose tables
Display records in grid or in text boxes.
Adapter & Dataset Context Menu
• Adapter:
–
–
–
–
Configure Adapter
Generate dataset
Preview data
Properties:
• Select/Insert/Update/DeleteCommand
• Dataset:
– View Schema: Dataset/XML
Using Tool Box’s Data Tab
• Creating a Connection, setting up a Data
Adapter, and generating a dataset:
– Drag OledbDataAdapter (or database’s table) to
the form.
– Use the Data Adapter Wizard to configure the
Adapter.
– Right Click the Adapter to preview data and
creating dataset.
• Bind the dataset to controls.
Data Binding
• Connect a control or property to one or
more data elements.
Binding DataGrid
• From Server Explorer, drag the table from a
database connection (or from Data tab, drag a
oleDbAdapter) onto the form.
• Create dataset.
• Drag DataGrid and set the DataSource and Data
Member property.
• Use adapter’s Fill method to load the dataset.
– OleDbDataAdapter1.Fill(DataSet11
Introduction to ADO.Net
Programming
Import NameSpace
• The Imports statement must appear before all
other declarations in a file and cannot appear
inside a class or module declaration.
– Imports System.Data.OleDb
– Public Class Form1
Connection Object
•
Example:
– dim strConn as string ="Provider=Microsoft.Jet.OLEDB.4.0;Data Source =
c:\sales2k.mdb"
– dim objConn as new OledbConnection(strConn)
– objConn.open()
• Basic Methods:
– Open, Close
Command Object
• The command object allows us to execute a SQL
statement.
• Properties:
– CommandType: SQL or stored procedure
– CommandText: SQL statement
– Connection
• Basic Methods:
– ExecuteReader: Creates a DataReader object that
contains the results of the query.
– ExecuteNonQuery: Execute SQL’s INSERT, DELETE,
UPDATE statements.
ExecuteReader Example
dim strConn as string
="Provider=Microsoft.Jet.OLEDB.4.0;Data Source =
c:\sales2k.mdb"
dim objConn as new OledbConnection(strConn)
dim strSQL as string = "select * from customer;"
dim objComm as new OledbCommand(strSQL,objConn)
dim Results as string
objConn.open()
dim objDataReader as oledbDataReader
objDataReader=objComm.executeReader()
DataReader Object
• It is read-only and forward-only cursor.
• Basic Methods:
– Read: Reads the current record and advances
the pointer to the next record.
– Close: Closes the dataReader.
Read Records in a DataReader
• dim Results as string
• do while objDataReader.Read()=true
Results+=objDataReader("cid") + “ “ + objDataReader("Cname") + vbCrLF
• loop
• Textbox1.text=Results
• Note: objDataReader.Item(0)
• Note: objDataReader.Item(“cid”)
Add Items from a DataReader to a Listbox
Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source =
c:\sales2k.mdb"
Dim objConn As New OleDbConnection(strConn)
Dim strSQL As String = "select cid from customer;"
Dim objComm As New OleDbCommand(strSQL, objConn)
objConn.Open()
Dim objDataReader As OleDbDataReader
objDataReader = objComm.ExecuteReader()
Do While objDataReader.Read() = True
LISTBOX1.Items.Add(objDataReader("cid"))
Loop
Display Selected Customer’s Record
Private Sub ListBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles ListBox1.SelectedIndexChanged
Dim strSQL As String = "select * from customer where cid = '" & ListBox1.SelectedItem
& "'"
Dim objComm As New OleDbCommand(strSQL, objConn)
objConn.Open()
Dim objDataReader As OleDbDataReader
objDataReader = objComm.ExecuteReader()
If objDataReader.Read = True Then
TextBox1.Text = objDataReader("Cname")
TextBox2.Text = objDataReader("City")
TextBox3.Text = objDataReader("rating")
Else
MessageBox.Show("record not found")
End If
objConn.Close()
End Sub
Insert a New Record Using ExecuteNonQuery
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
Handles Button1.Click
Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb"
Dim objConn As New OleDbConnection(strConn)
Dim strSQLInsert As String
strSQLInsert = "Insert into Customer values ('"
strSQLInsert = strSQLInsert & TextBox1.Text & "','" & TextBox2.Text & "','"
strSQLInsert = strSQLInsert & TextBox3.Text & "','" & TextBox4.Text & "')"
Dim objComm As New OleDbCommand(strSQLInsert, objConn)
objConn.Open()
objComm.ExecuteNonQuery()
objConn.Close()
End Sub
Demo
• Create a project that do the following tasks:
– Use a DataReader to retrieve customer IDs and
populate a listbox.
– Select a new rating from radio buttons for the
selected customer.
– Update customer’s rating using the
ExecuteNonQuery method of a Command
object.
Declare OleDB objects and create listbox
Imports System.Data.OleDb
Public Class Form3
Inherits System.Windows.Forms.Form
Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source =
c:\sales2k.mdb"
Dim objConn As New OleDbConnection(strConn)
Dim strSQL As String = "select cid from customer;"
Dim objComm As New OleDbCommand(strSQL, objConn)
Private Sub Form3_Load(ByVal sender As System.Object, ByVal e As System.EventArgs)
Handles MyBase.Load
objConn.Open()
Dim objDataReader As OleDbDataReader
objDataReader = objComm.ExecuteReader()
Do While objDataReader.Read() = True
ListBox1.Items.Add(objDataReader("cid"))
Loop
objConn.Close()
End Sub
Update customer rating
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
Handles Button1.Click
objConn.Open()
Dim newRating As String
If RadioButton1.Checked = True Then
newRating = "A"
ElseIf RadioButton2.Checked Then
newRating = "B"
Else
newRating = "C"
End If
Dim strSQLUpd As String = "Update customer set rating = '" & newRating & "'"
strSQLUpd = strSQLUpd & " where cid='" & ListBox1.SelectedItem & "'"
Dim objCommUpd As New OleDbCommand(strSQLUpd, objConn)
objCommUpd.ExecuteNonQuery()
objConn.Close()
End Sub