WCF DataServices and Total Number of Rows

Cristian Merighi (Thursday, November 25, 2010)

OData protocol and ASP.NET Ajax 4 tools: how to use them in order to retrieve, along with a subset of rows, the total row number of elements stored in database.

ASP.NET Ajax 4 just came out of the box in its final vest, and white papers don't offer - so far - omnicomprehensive support for all the available features.
That's why I decided to pin newly discovered nuggets, as soon as I get 'em, here on my online diary.

This article is about data-paging (generally speaking). In particular it's about retrieving the total number of rows (stored in database and given a particular filter clause) via WCF Data Services using OData protocol URI conventions.

We're going to use retrieve data from a client browser through javascript scripts.
Let's start by loading necessary scripts (à la ASP.Net 4, I assume that the following code would result clear, otherwise please refer to this documentation or similar).

<script type="text/javascript">
//<![CDATA[
// jQuery has been already (statically) loaded
    Sys.require([Sys.components.openDataServiceProxy, Sys.components.dataView]);
//]]>
</script>

Now the call to a System.Data.Services.DataService that exposes data in a "RESTful" fashion.

<script type="text/javascript">
//<![CDATA[

var totalCount;
Sys.onReady(function () {
    // setting default values for our hypothetical Sys.UI.DataView.
    $().dataView.defaults = {autoFetch: true, itemTemplate: '#dataViewItemTemplate'};
    // instantiate the jQuery way the web service proxy.
    var proxy = $.openDataServiceProxy('<%=ResolveClientUrl("~/services/modelservice.svc") %>');
    var topRows = 3;
    // I use this utility (Sys.Data.OopenDataQueryBuilder) to ease the URI formatting.
    var qb = new Sys.Data.OpenDataQueryBuilder('BudgetSet');
    // IMPORTANT: set the $inlinecount parameter to allpages:
    // the result of the request will be enriched with a total count information.
    qb.set_inlineCount('allpages');
    qb.set_orderby('EndDate desc,StartDate');
    // Limit the number of rows to be returned.
    qb.set_top(topRows);
    // Filter clause:
    qb.set_filter("EndDate le datetime'<%=DateTime.Today.ToString("yyyy-MM-dd") %>'");
    proxy.query(/* here it is the formatted URI -> */qb.toString(),
        // And now the black magic!
        // Among the arguments passed to the callback function for successful retrieval...
        // the 4th(!) contains the information that we need: the totalcount.
        function(results, ctx, uri, c){
        // let us store it...
        totalCount = c.count;
        // let us use the retrieved data to feed the dataview...
        $("#expiredBudgets").dataView({ data: results });
    });
});
//]]>
</script>

The interface implementation is omitted, how you will exploit the total row count information is less important than how to get it!
Hope it helped.

Take care. Bye.

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