Question

We are developing an ASP.Net web application with a SQL Server database and would like to populate an ASP.Net label control with the total number of students who are enrolled at the school whenever the home page is displayed.

We created the following strongly typed controls with the dataset designer:

DataTable: Students
DataSet: DataSetAllStudents
TableAdapter: StudentsTableAdapter

In the VB.Net code-behind file I used the following code to start the process of obtaining a total count of enrolled students.

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

    Dim studentsAdapter As New DataSetAllStudentsTableAdapters.StudentsTableAdapter
    Dim studentsTableRow As Knowledge_Academy.Students

    studentsTableRow = studentsAdapter.GetData

End Sub

We get an error on this line of code:

studentsTableRow = studentsAdapter.GetData

This is the error:

Value of type 'Knowledge_Academy.DataSetAllStudents.StudentsDataTable' cannot be 
converted to 'Knowledge_Academy.Students'.

GetData contains the query that will return the total number of enrolled students. We would also like to know how to get the value returned into this ASP.Net label control.

<asp:Label ID="LabelTotalNumberOfStudents" runat="server" Text="Label"></asp:Label>

Answer 1

First, ensure that you load the data only on the first load and not on every postback. Second, since GetData returns a DataTable with all rows you can use it’s Rows.Count property:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    If Not Page.IsPostBack Then
        Dim daStudents = New DataSetAllStudentsTableAdapters.StudentsTableAdapter()
        Dim tblStudents = studentsAdapter.GetData()
        LblStudentNumber.Text = String.Format("{0}", tblStudents.Rows.Count)
    End If
End Sub

Of course it would be better to add a new query to the TableAdapter that returns a scalar value with the number of students. That would require much less resources.