SEO Friendly Paging with ASP.NET 2.0 Data Controls

ASP.NET has lots of "out of the box" features that make the display of data easy, including pageable GridViews and DataGrids with little or no code. But the stock paging mechanism uses javascript to cause the postback, and the url of the new "page" doesn't change. This is not "SEO friendly", because the Googlebot and other search engine crawlers click on the links, and see the result as a page they've already requested, so it doesn't get indexed.

From an SEO (Search Engine Optimization) standpoint, having your pageable display passed up by search bots is not good. Here is a way to handle paging with Data Controls such as the DataList - which doesn't offer native paging -- and ensure that each new page request is a unique url that the search engines will slurp up and index.

 For our sample data, we will cheat a little and use a custom RSS search to google blog search, returning the results as RSS which can be loaded directly into a DataSet via the ReadXml method. We will also cache the DataSource in Session so that we do not have to make a separate webrequest each time we request the next page of results. We will use the PagedDataSource class to handle the paging for the DataList. PagedDataSource encapsulates the paging-related properties of a data-bound control (such as DataGrid, GridView, DetailsView, FormView, Repeater or DataList) that allow it to perform paging. By using the PagedDataSource as the datasource for one of these controls, you can easily enable paging features even if the control does not support paging on its own.

 PagedDataSource uses the best available method to enumerate over the data belonging to the current page. If the underlying data source supports indexed access (such as System.Array and System.Collections.IList), this class uses it. Otherwise, it uses the enumerator created by the GetEnumerator method. You can use the PagedDataSource with a DataTable (which does not support IEnumerable or IList) by simply binding to its DefaultView (DataView) -- which does support this.

 PagedDataSource offers all the members that you would expect to perform paging - including CustomPaging:

•   AllowCustomPaging  Gets or sets a value indicating whether custom paging is enabled in a data-bound control.
•   AllowPaging  Gets or sets a value indicating whether paging is enabled in a data-bound control.
•   AllowServerPaging  Gets or sets a value indicating whether server-side paging is enabled.
•   Count  Gets the number of items to be used from the data source. 
•   CurrentPageIndex  Gets or sets the index of the current page. 
•   DataSource  Gets or sets the data source.
•   DataSourceCount  Gets the number of items in the data source.
•   FirstIndexInPage  Gets the index of the first record displayed on the page.
•   IsCustomPagingEnabled  Gets a value indicating whether custom paging is enabled.
•   IsFirstPage  Gets a value indicating whether the current page is the first page.
•   IsLastPage  Gets a value indicating whether the current page is the last page.
•   IsPagingEnabled  Gets a value indicating whether paging is enabled.
•   IsReadOnly  Gets a value indicating whether the data source is read-only.
•   IsServerPagingEnabled  Gets a value indicating whether server-side paging support is enabled.
•   IsSynchronized  Gets a value indicating whether access to the data source is synchronized (thread-safe).
•   PageCount  Gets the total number of pages necessary to display all items in the data source.
•   PageSize  Gets or sets the number of items to display on a single page.
•   SyncRoot  Gets the object that can be used to synchronize access to the collection.
•   VirtualCount  Gets or sets the virtual number of items in the data source when custom paging is used.
  

A page with a DataList needs no special items on it except for  2 LinkButtons that provide the  <  and  > functionality to move forward or backward one "page". What's important is the codebehind, which implements the PagedDataSource:

using System;
using System.Data;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace SEOFriendlyPaging
{
    public partial class _Default : Page
    {
        protected PagedDataSource pagedData = null;
        protected string srchTerm = "ASP.NET"; // use a default search term

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                // if initial page load---
                pagedData = new PagedDataSource();
            }
            else
            {
                pagedData = (PagedDataSource) Session[srchTerm];
            }
            BindPaged();
        }

        public void Prev_Click(object obj, EventArgs e)
        {
            int newPageIndex = ((int) (pagedData.CurrentPageIndex - 1));
            pagedData.CurrentPageIndex = newPageIndex;
            Response.Redirect(Request.CurrentExecutionFilePath + "?Page=" +
                              newPageIndex.ToString());
        }

        public void Next_Click(object obj, EventArgs e)
        {
            int newPageIndex = ((int) (pagedData.CurrentPageIndex + 1));
            pagedData.CurrentPageIndex = newPageIndex;
            Response.Redirect(Request.CurrentExecutionFilePath + "?Page=" +
                              newPageIndex.ToString());
        }


        private void BindPaged()
        {
            if (txtSearch.Text != "")
                srchTerm = txtSearch.Text;
            DataView dv = null;
            if (Session[srchTerm] == null)
            {
                string baseUrl = "http://blogsearch.google.com/blogsearch_feeds?hl=en&q=";
                string baseUrlEnd = "&num=100&output=rss";
                if (srchTerm == "") srchTerm = "ASP.NET";
                string fullSearchUrl = baseUrl + srchTerm + baseUrlEnd;
                DataSet ds = new DataSet();
                ds.ReadXml(fullSearchUrl);
                dv = ds.Tables[2].Copy().DefaultView;
                Session[srchTerm] = pagedData;
            }
            else
            {
                pagedData = (PagedDataSource) Session[srchTerm];
                dv = (DataView) pagedData.DataSource;
            }
            pagedData.DataSource = dv;
            pagedData.AllowPaging = true;
            pagedData.PageSize = 5;
            if (Request.QueryString["Page"] == null)
                pagedData.CurrentPageIndex = 0;
            else
            {
                int pg = int.Parse(Request.QueryString["Page"]);
                if (pg < 0) pg = 0;
                pagedData.CurrentPageIndex = pg;
            }
            btnPrev.Visible = (!pagedData.IsFirstPage);
            btnNext.Visible = (!pagedData.IsLastPage);
            dlSEOFriendly.DataSource = pagedData;
            dlSEOFriendly.DataBind();
        }

        protected void btnSearch_Click(object sender, EventArgs e)
        {
            BindPaged();
        }
    }
}

using System;
using System.Text;
using System.Web.UI.WebControls;

namespace SEOFriendlyPaging
{
    public static class Pager
    {
        public static string CreatePagerLinks(PagedDataSource pgdDataSource, string BaseUrl)
        {
            StringBuilder sbPager = new StringBuilder();
            //sbPager.Append("More: ");
            if (!pgdDataSource.IsFirstPage)
            {
                // first page link
                sbPager.Append("<a href=\"");
                sbPager.Append(BaseUrl);
                sbPager.Append("\">|<</a> ");
                if (pgdDataSource.CurrentPageIndex != 1)
                {
                    // previous page link
                    sbPager.Append("<a href=\"");
                    sbPager.Append(BaseUrl);
                    sbPager.Append("&page=");
                    sbPager.Append(pgdDataSource.CurrentPageIndex.ToString());
                    sbPager.Append("\" alt=\"Previous Page\"><<</a>  ");
                }
            }
            // calc low and high limits for numeric links
            int intLow = pgdDataSource.CurrentPageIndex - 1;
            int intHigh = pgdDataSource.CurrentPageIndex + 3;
            if (intLow < 1) intLow = 1;
            if (intHigh > pgdDataSource.PageCount) intHigh = pgdDataSource.PageCount;
            if (intHigh - intLow < 5) while ((intHigh < intLow + 4) && intHigh < pgdDataSource.PageCount) intHigh++;
            if (intHigh - intLow < 5) while ((intLow > intHigh - 4) && intLow > 1) intLow--;
            for (int x = intLow; x < intHigh + 1; x++)
            {
                // numeric links
                if (x == pgdDataSource.CurrentPageIndex + 1) sbPager.Append(x.ToString() + "  ");
                else
                {
                    sbPager.Append("<a href=\"");
                    sbPager.Append(BaseUrl);
                    sbPager.Append("&Page=");
                    sbPager.Append(x.ToString());
                    sbPager.Append("\">");
                    sbPager.Append(x.ToString());
                    sbPager.Append("</a>  ");
                }
            }
            if (!pgdDataSource.IsLastPage)
            {
                if ((pgdDataSource.CurrentPageIndex + 2) != pgdDataSource.PageCount)
                {
                    // next page link
                    sbPager.Append("<a href=\"");
                    sbPager.Append(BaseUrl);
                    sbPager.Append("&Page=");
                    sbPager.Append(Convert.ToString(pgdDataSource.CurrentPageIndex + 2));
                    sbPager.Append("\">>></a>  ");
                }
                // last page link
                sbPager.Append("<a href=\"");
                sbPager.Append(BaseUrl);
                sbPager.Append("&Page=");
                sbPager.Append((pgdDataSource.PageCount - 1).ToString());
                sbPager.Append("\">>|</a>");
            }
            // convert the final links to a string and  return for assignment
            return sbPager.ToString();
        }
    }
}

This article looks good. Can we have it tweaked to work for multiple grids by doing something like Grid1Page=1&Grid2Page=2 and on hyperlinks to persist both the Grid Page Indexes?

Hi Peter, thanks for posting this, i have had a link to this article  for a while always knowing will have to refer to it some point. Havent used your code as is but striped out the gernerating html links section.

Great stuff thanks.

Anthony