Using Methods with Object Oriented Database Development with VB.NET 2005 - Developing methods with parameters having default values

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Sometimes, it may be necessary for one or more parameters of a method to have default values. If the calling program didn't pass any values to the parameters, the default values will be taken into consideration. If the user passes values to the parameters, the default values get replaced with the values sent by the calling program.

Let us modify the same method listed in the previous section:

PublicFunction isEmployeeExist(Optional ByVal empno As String = Nothing)
As Boolean
        Dim cn As New SqlConnection("Data Source=.sql2k5;initial
catalog=sample;user id=sa;password=eXpress2005")
        If Not empno Is Nothing Then
            m_empno = empno
        End If
        Dim cmd As New SqlCommand("select 'exists' from sample.dbo.emp
where empno='" & m_empno & "'", cn)
        Dim found As Boolean = False
        Try
            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

From the method above, you can understand that the parameter is mentioned as optional. Currently, I assigned the default value for the "empno" as "nothing." If the calling program doesn't pass any value to this method, it takes "m_empno" as the value to search. To execute the above method, you can work with the same code available in the previous section, or you can further modify it 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
            ep.m_empno = Me.txtEmpno.Text
            If ep.isEmployeeExist() 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: Dealing with method overloading to attain more flexibility >>
 

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