Using Methods with Object Oriented Database Development with VB.NET 2005 - Developing methods which return objects
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In the previous section, we developed methods accepting parameters as objects. In this section, we shall examine the methods returning objects. Let us look at the code first:
PublicFunction getEmployee(ByVal empno As String) As Emp
Dim objEmp As New Emp
Dim cn As New SqlConnection("Data Source=.sql2k5;initial
catalog=sample;user id=sa;password=eXpress2005")
Dim cmd As New SqlCommand("select * from sample.dbo.emp where
empno='" & empno & "'", cn)
Try
objEmp.m_empno = empno
cmd.Connection.Open()
Dim rd As SqlDataReader = cmd.ExecuteReader
If rd.Read() Then
objEmp.m_ename = rd("ename")
objEmp.m_sal = rd("sal")
objEmp.m_deptno = rd("deptno")
Else
Throw New Exception("Employee not found")
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 objEmp
End Function
Within the above code, you can observe the object named "objEmp." I created it just to place values in it and return the same. Through SqlDataReader, I retrieved all the values and assigned them to the fields of "objEmp." Finally, I returned the same.
To execute the above code, I wrote the following code:
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
Dim objReturned As Emp
objReturned = ep.getEmployee(Me.txtEmpno.Text)
Me.txtDeptno.Text = objReturned.m_deptno
Me.txtEname.Text = objReturned.m_ename
Me.txtSal.Text = objReturned.m_sal
Catch ex As Exception
Me.lblErrMsg.Text = ex.Message
End Try
End Sub
The most important issue is the object named "objReturned." It is not a complete object (as it is not declared with a "new" operator). It is simply an "object Reference." That means it refers to some other object assigned to it (but it doesn't allocate any memory by itself). In the current case, "getEmployee" creates memory allocation and refers it with "objEmp." Later the same is assigned to "objReturned" (which "refers" to the memory allocated by some other object).
In this article, I simply wanted to explain the topics related to OOPS along with data access. The sample codes given in this article are neither the best in performance nor the best in programming methodologies. My upcoming articles will deal with these issues.
Any feedback, suggestions, bugs, errors, improvements etc., are highly appreciated at jag_chat@yahoo.com.
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