Using Methods with Object Oriented Database Development with VB.NET 2005
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This is the second article in a series on developing object oriented database applications using Visual Basic.NET 2005. In this article, I shall deal with the concept of “methods” a bit more in depth, along with data access.
A downloadable file for this article is available
here.
For this article, I assume that you know enough about the basics of working with VB.NET controls, ADO.NET, and so forth using Visual Basic.NET 2005. Even though this article only gives you the basics of OOP along with database development, I shall extend it in the form of a series to cover most advanced topics in Visual Basic.NET 2005. If you are very new to OOP in VB.NET, I request that you go through my first article in this series.
The entire source code for this article is available in the form of a downloadable zip file. The solution was developed using Microsoft Visual Studio 2005 Professional Edition with Microsoft SQL Server 2005 Developer Edition on Microsoft Windows Server 2003 Enterprise Edition. Even though I believe that the source code available with this article can work with Microsoft Visual Studio.NET 2003/2002, I didn't really test it in any other environment. I request that you post in the discussion area, if you have any problems with execution.
To make this article simple, I created a sample database named "sample," with a table "emp" containing the columns empno (string), ename (string), sal (double) and deptno (integer), and a few rows.
Developing methods which return Boolean values
In my previous article, I introduced classes, members, fields, methods and objects. Now, in this article, we shall look a bit more in depth into classes and methods.
The following is a new method I added to the class "Emp:"
PublicFunction isEmployeeExist(ByVal empno As String) As Boolean
Dim cn As New SqlConnection("Data Source=.sql2k5;initial
catalog=sample;user id=sa;password=eXpress2005")
Dim cmd As New SqlCommand("select 'exists' from sample.dbo.emp
where empno='" & empno & "'", cn)
Dim found As Boolean = False
Try
m_empno = empno
cmd.Connection.Open()
Dim rd As SqlDataReader = cmd.ExecuteReader
If rd.Read() Then
found = True
End If
Catch ex As Exception
Throw New Exception(ex.Message)
Finally
If cmd.Connection.State = ConnectionState.Open Then
cmd.Connection.Close()
End If
cmd.Dispose()
cn.Dispose()
End Try
Return found
End Function
The above method can be considered to be a "method returning a value." In this case, we are returning a Boolean value. To execute the above method, I modified the "btnSearch_click" as follows:
PrivateSub btnSearch_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnSearch.Click
Me.lblErrMsg.Text = ""
Try
Dim ep As New Emp
If ep.isEmployeeExist(Me.txtEmpno.Text) Then
ep.load(Me.txtEmpno.Text)
Me.txtDeptno.Text = ep.m_deptno
Me.txtEname.Text = ep.m_ename
Me.txtSal.Text = ep.m_sal
Else
Throw New Exception("Employee not found")
End If
Catch ex As Exception
Me.lblErrMsg.Text = ex.Message
End Try
End Sub
Next: Developing methods with parameters having default values >>
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