Introduction
Anybody in the DB world knows what paging database results is and its effect. From the time I had started getting into good old classic ASP, I was intrigued with the ability to divide large sets of data into sections of x records per page. One thing that I didn't like about paging is that it seemed sites incorporated just a < Prev and Next > link on the search results page. I wasn't satisfied with such a lackluster paging technique, and from there I searched high and low on every ASP Web site I could find to see if there was code to show more advanced paging options, such as how many pages were remaining to be paged through, or, if the next page was the last page of results, how many records were on that last page.
Now, if anyone has looked into the Microsoft .NET SDK and Quickstart samples you will find custom paging samples, but it's the usual next and prev stuff. Now let's see how we can kick this paging up a notch and tell us more detail about our data output.
Accessing our Data
The first step is of course to query our database, and send our data into our datagrid. The first thing we should concern ourselves with in any .Net page is that we import the necessary namespaces for our app. In this case, as with most data access apps, I'm importing System.Data and System.Data.SqlClient for SQL Server. If you use MS Access or another database then System.Data.OleDb namespace and associated classes will work just fine, providing you modify the connection variables and data adapters.
This importing of namespaces is all done before our script tags like so:
<%@ Import Namespace = "System.Data" %>
<%@ Import Namespace = "System.Data.SqlClient" %>
Now, within our server-side script tags we include our object-oriented stuff – our Subroutine to access our database and bind our result set into our ASP.NET Datagrid. This subroutine, BindSQL() needs to first create all of our variables that we'll use:
Sub BindSQL()
Dim MyConnection As SqlConnection
Dim DS as DataSet
Dim MyCommand As SqlDataAdapter
Dim RcdCount As Integer
'Our SQL string
Dim sqlStr As String = "SELECT titles.title, authors.au_lname, " & _
"authors.au_fname, titles.price " & _
"FROM authors INNER JOIN titleauthor ON " & _
"authors.au_id = titleauthor.au_id " & _
"INNER JOIN titles ON " & _
"titleauthor.title_id = titles.title_id"
'The connection to our database
Dim strConn As String = "server=(local);uid=sa;pwd=;" & _
"database=pubs;Trusted_Connection=yes;"
Next we need to instantiate our connection and command object, and the fill our DataSet object with the results of the SQL query:
...
'Open up our connection with our connection object
MyConnection = New SQLConnection(strConn)
'To execute our Sql Statement and provide our active connection
MyCommand = NewSqlDataAdapter(sqlStr, MyConnection)
'Create instance of DataSet object and fill our predetermined
'datagrid with it and we name it
DS = new DataSet()
MyCommand.Fill(DS, "pubs")
...
Now comes the one part that we'll used for our custom paging – the record count, and you'll see it quite different than our classic ASP way.
RcdCount = DS.Tables("pubs").Rows.Count.ToString()
Now that we have this total count of the records in the DataSet, we'll save it to a global variable, since we'll want to access it from other subroutines. The variable ResultCount should be defined in global-scope, as an Integer.
ResultCount = RcdCount
Next, we display the number of records found in a label control:
RecordCount.Text = "" & RcdCount & " records found"
Finally, at this point, we can bind our DataSet to the DataGrid and display a label illustrating what page of results we're currently viewing: which will display :
Pubs.DataSource = DS
Pubs.Databind()
lblPageCount.Text = "Page " & Pubs.CurrentPageIndex + 1 & " of " & Pubs.PageCount
At this point, we need to determine if we need to show the Next/Prev links, as well as the First Page/Last Page links:
'Do we want to show the prev/First Page buttons?
If Pubs.CurrentPageIndex <> 0 Then
Call Prev_Buttons()
Firstbutton.Visible = true
Prevbutton.Visible = true
Else
Firstbutton.Visible = false
Prevbutton.Visible = false
End If
'Do we want to show the Next/Last Page buttons?
If Pubs.CurrentPageIndex <> (Pubs.PageCount-1) then
Call Next_Buttons()
NextButton.Visible = true
Lastbutton.Visible = true
Else
NextButton.Visible = false
Lastbutton.Visible = False
End If
End Sub
The HTML Portion
In our HTML section we need a couple of label controls to display various bits of information, such as what page we are currently viewing, how many total records there are, etc. We also need a DataGrid, to which we are binding the database results to. Don't forget to put the DataGrid in a WebForm (a
The event handler for the four LinkButtons (PagerButtonClick) must display the appropriate page of data, be it the next page, the previous page, the first page, or the last page. Which page to display, of course, depends on what LinkButton the user clicked. The PagerButtonClick (shown below) uses the CommandArgument passed in from the LinkButton Web controls to determine which control was clicked, and then takes the appropriate action.
Sub PagerButtonClick(sender As Object, e As EventArgs)
'used by external paging UI
Dim arg As String = sender.CommandArgument
Select arg
Case "next": 'The next Button was Clicked
If (Pubs.CurrentPageIndex < (Pubs.PageCount - 1)) Then
Pubs.CurrentPageIndex += 1
End If
Case "prev": 'The prev button was clicked
If (Pubs.CurrentPageIndex > 0) Then
Pubs.CurrentPageIndex -= 1
End If
Case "last": 'The Last Page button was clicked
Pubs.CurrentPageIndex = (Pubs.PageCount - 1)
Case Else: 'The First Page button was clicked
Pubs.CurrentPageIndex = Convert.ToInt32(arg)
End Select
'Now, bind the data!
BindSQL()
End Sub
The RePage event handler, which is called when the "Change Pagesize" button is clicked, simply resets the DataGrid's CurrentPageIndex property back to 0 and rebinds the database data:
Sub Repage(sender As Object, e As EventArgs)
Pubs.CurrentPageIndex = 0
BindSQL()
End Sub
Finally, the last two server-side subroutines are two meager helper subroutines, Next_Buttons() and Prev_Buttons(), which display the correct text for each of the LinkButtons. These two subs, which are called from BindSQL(), can be seen below:
Sub Prev_Buttons()
Dim PrevSet As String
If Pubs.CurrentPageIndex+1 <> 1 and ResultCount <> -1 Then
PrevSet = Pubs.PageSize
PrevButton.Text = ("< Prev " & PrevSet)
If Pubs.CurrentPageIndex+1 = Pubs.PageCount Then
FirstButton.Text = ("<< 1st Page")
End If
End If
End Sub
Sub Next_Buttons()
Dim NextSet As String
If Pubs.CurrentPageIndex+1 < Pubs.PageCount Then
NextSet = Pubs.PageSize
NextButton.Text = ("Next " & NextSet & " >")
End If
If Pubs.CurrentPageIndex+1 = Pubs.PageCount-1 Then
Dim EndCount As Integer
EndCount = ResultCount - (Pubs.PageSize * (Pubs.CurrentPageIndex+1))
NextButton.Text = ("Next " & EndCount & " >")
End If
End Sub
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