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Every once in a while I come across the task of displaying a large number of records in ASP pages. The good example is displaying the results of a search. Most of the time I do not know the number of records that I have to display in advance. In addition to this, as the usage of the application growth the size of the database will grow accordingly. That leaves me as well as anyone with the similar application requirements no other choice, but to develop some kind of algorithm to display records in the smaller chunks - pages.
Everyone is familiar with the way search results are displayed by Internet search engines. You get the first page of results that are limited to some number of records (20 for example) and some navigational links to go to the first, previous, next or the last page. Some sites give you the ability to go directly to specific page number, some use a mixture of both.
So how does one implements record paging mechanism in ASP? Specifically, how do we implement record paging using ADO?
Let’s pretend that we have a database with the table called tblItem that is used to store information about our Items (whatever they are?). Let me also imagine that one of the fields in tblItem called ItemName. We are given a task of creating a set of pages to give a user an ability to search for the items by the ItemName field. We decided to make a set of two pages. One page will display the search form and one for the results of the search.
Please excuse me, but I will skip all the variable declarations and HTML formatting.
First page should be easy. It’s a standard HTML form that could look something similar to this:
<FORM ACTION="results.asp" METHOD="GET">
Item Name: <INPUT TYPE="text" NAME="Keyword"> <INPUT TYPE="submit" VALUE=" Find ">
Second page is where all the magic should happen. This is what the second page (results.asp) should be able to do:
- Receive the Keyword that user have entered.
- Search the database for records containing Keyword.
- Display a page of resulting records.
- Provide user with some navigation links to display more pages of results if needed.
1. Receive the Keyword
Receiving the Keyword is as easy as:
Keyword = Trim(Request.QueryString("Keyword"))
2. Search the database for records containing Keyword
Now we have everything we need to get an ADO recordset with the items that contain our keyword in their ItemName.
First we create a sql statement that will do the search:
SQL = "SELECT * FROM tblItem WHERE ItemName LIKE '%" & Replace(Keyword, "'", "''") & "%'"
Notice that I’ve used Replace function to double single quotes in the search string. Without it if user enters a single quote in his/her Keyword you will receive an error.
' Create and open ADO recordset
Set RS = Server.CreateObject("ADODB.Recordset")
RS.CursorLocation = 3 ' adUseClient
RS.Open SQL, strConnectionString
Notice that I set
CursorLocation property of the recordset to
adUseClient (3). We have to do it in order to be able to use some of the properties of this recordset later. I left out the CursorType and LockType parameters, because the defaults
adLockReadOnly are exactly what we need in this case to get the best performance.
4. Provide navigation links.
Yes it is a fourth step. I did leave the third step (displaying of the results) for the last because in order for us to display the records we need to figure some things out. I also think it is better to create and display navigation links on the top of the page before the results.
At this point we have to figure out couple of things: do we have any results from our search and if so how many pages of results do we have?
Presence of the results is easily determent by checking the EOF property of the recordset:
If RS.EOF Then
... ' Clean up
... ' Do the no results HTML here
Response.Write "No Items found."
... ' Done
The number of pages we have is obviously depends on the number of items we want to display per page.
' Set the page size of the recordset
RS.PageSize = nItemsPerPage
' Get the number of pages
nPageCount = RS.PageCount
Now we need to talk about the current page number. Since we want this page (results.asp) to be able to display any one of the pages of results we have to have a way to specify which page will the user see right now. We will do it by passing an additional parameter to our results.asp script that we will call "Page". So the link to our page could look like this:
With that said we can figure out the number of the page that is requested by the user by simple checking Page parameter:
nPage = CLng(Request.QueryString("Page"))
We need to make sure that the number of page requested by user is within the acceptable range and fix it if needed:
If nPage < 1 Or nPage > nPageCount Then
nPage = 1
Now we can create our navigation links by simply linking to this page with the same value for Keyword and the specific page number. For example:
' First page
Response.Write "<A HREF=""results.asp?Keyword=" & Keyword & "&Page=1"">First Page</A>"
' Previous page:
Response.Write "<A HREF=""results.asp?Keyword=" & Keyword & "&Page=" & nPage - 1 & """>Prev. Page</A>"
' Next page
Response.Write "<A HREF=""results.asp?Keyword=" & Keyword & "&Page=" & nPage + 1 & """>Next Page</A>"
' Last page
Response.Write "<A HREF=""results.asp?Keyword=" & Keyword & "&Page=" & nPageCount & """>Last Page</A>"
' 15th page:
Response.Write "<A HREF=""results.asp?Keyword=" & Keyword & "&Page=15"">15th Page</A>"
3. Display a page of resulting records.
All we have left is to display one page of results:
' Position recordset to the correct page
RS.AbsolutePage = nPage
' Display the page of results
Do While Not ( RS.Eof Or RS.AbsolutePage <> nPage )
Response.Write RS("ItemName") & "<br>"
That is it. Sample that I have included here is a bit more complex, because I've combined both HTML search form and displaying of the results in one ASP page. That is why there is an additional Mode parameter is being used in every link. All the code concerning displaying of the results of the search is in the