1. Database Handling Class and Service

2. ADO.Net
Objects
Database
Classes
Data Source
Forms
Reports

3. Single-Record-Handling Classes
Retrieves a single record from the database and makes it available to your application in the form of an object.
The fields in the record are exposed as the object’s properties.
Any actions performed by the data (updates, calculations, etc.) are exposed as the object’s methods.

4. Single-Record-Handling Class Example
Imports System.Data.OleDb
Public Class Customer
Public cid As String
Public CName As String
Public City As String
Public Rating As String
Private hiddenexist As Boolean
Private cn As OleDb.OleDbConnection
Public ReadOnly Property RecExist() As Boolean
Get
RecExist = hiddenexist
End Get
End Property

5. Dim objConn As New OleDbConnection(strConn)
Public Sub getData(ByVal SearchID As String)
Dim strConn As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\SalesDB2007.accdb”
Dim objConn As New OleDbConnection(strConn)
Dim strSQL As String = "select * from customer where cid = '" & SearchID & "'"
Dim objComm As New OleDbCommand(strSQL, objConn)
objConn.Open()
Dim objDataReader As OleDbDataReader
objDataReader = objComm.ExecuteReader()
If objDataReader.Read() = False Then
hiddenexist = False
Else
hiddenexist = True
cid = objDataReader("cid")
CName = objDataReader("CName")
City = objDataReader("City")
Rating = objDataReader("Rating")
End If
objConn.Close()
End Sub

6. Public Sub SaveNew()
Dim strConn As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\SalesDB2007.accdb"
Dim objConn As New OleDbConnection(strConn)
objConn.Open()
Dim strSQLInsert As String
strSQLInsert = "Insert into Customer values ('"
strSQLInsert = strSQLInsert & cid & "','" & CName & "','"
strSQLInsert = strSQLInsert & City & "','" & Rating & "')"
Dim objCommInsert As New OleDbCommand(strSQLInsert, objConn)
objCommInsert.ExecuteNonQuery()
objConn.Close()
End Sub

7. Enter CID, then use the GetData method to retrieve record

8. Code Example
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim myCust As New Customer()
myCust.getData(TextBox1.Text)
If myCust.RecExist Then
TextBox2.Text = myCust.CName
TextBox3.Text = myCust.City
TextBox4.Text = myCust.Rating
Else
MessageBox.Show("record not exist")
End If
End Sub

9. Using the SaveNew Method to Add A New Customer
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim newCust As New Customer()
newCust.cid = TextBox1.Text
newCust.CName = TextBox2.Text
newCust.City = TextBox3.Text
newCust.Rating = TextBox4.Text
newCust.SaveNew()
TextBox1.Text = ""
TextBox2.Text = ""
TextBox3.Text = ""
TextBox4.Text = ""
End Sub

10. From Class to Service

11. What is a service?
A service is a program that can be interacted with via well-defined message exchanges.

12. .Net Implements a service as an assembly
Basic unit of deployment.
Implemented as Dynamic Link Library, DLL.

13. Difference between Assembly and Class
A class defined in a project is available to that project only.
Once a class is compiled into an assembly it can be used by any projects.
To create an assembly:
Start a Class Library project

14. Steps to Create An Assembly
Start a Class Library project
Create classes
You can also use existing classes defined in other projects by Project/Add Existing Item
Save project
Select Build/Build to compile the code.
When the class library is compiled successfully, an assembly is created and stored in the project’s Bin/Release folder.
Example: If a testClassLib project is created in C:\VS2008Examples folder, then the assembly is found in:
C:\VS2008Examples\testClassLib\testClassLib\bin\Release

15. Using the Assembly
Reference the assembly: Project/Add Reference and use the Browse button to select the assembly.
Import the assembly.
If the class is created in ClassLibrary1 library project, then: Imports ClassLibrary1

16. Code Using the Class in Assembly Inserting a New Customer
Imports ClassLibrary1
Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim newCust As New Customer()
newCust.cid = TextBox1.Text
newCust.CName = TextBox2.Text
newCust.City = TextBox3.Text
newCust.Rating = TextBox4.Text
newCust.SaveNew()
TextBox1.Text = ""
TextBox2.Text = ""
TextBox3.Text = ""
TextBox4.Text = ""
End Sub
End Class