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HTTP Push from SQL Server — Comet SQL

, 27 Nov 2012
This article provides an example solution for presenting data in "real-time" from Microsoft SQL Server in an HTML browser. The article presents how to implement Comet functionality in ASP.NET and how to connect Comet with Query Notification from SQL Server.
// Copyright (c) 2010 Daniel Wojciechowski 
// E-mail: at gmail.com daniel.wojciechowski
//
// Permission is hereby granted, free of charge, to any person
// obtaining a copy of this software and associated documentation
// files (the "Software"), to deal in the Software without
// restriction, including without limitation the rights to use,
// copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following
// conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
// OTHER DEALINGS IN THE SOFTWARE.


Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequestHandler);
// Called when async postback ends
function EndRequestHandler(sender, args)
{   
    // this function is run after an Ajax partial postback occurs

    if(isPolling == 0)  // this "if" prevents from runing two requests
        longPolling();
}


function addLongPollingError(type, msg){
    $("#DebugLabel").html(
        "<div class='msg "+ type +"'>" + msg +"</div>" +
        "<button type='Button' onClick='longPolling()'>Connect again</button>"
    );
}

var isPolling = 0;
function longPolling()
{
    // prevent from runing two requests:
    // It is now commented because it is currently done in EndRequestHandler
    //if(isPolling>0)
    //    return;
        
    isPolling++;
    $.ajax({
        type: "GET",
        url: "CometAsyncHandler.ashx?waitTime=60", // one minute

        //async: true, 
        cache: false,
        //timeout:12000,

        success: function(data){ 
            isPolling--;
            if(data == "NEWDATAISAVAILABLE")
                RefreshData(); // this function is generated by using RegisterFunctionToPostBack()
            else if( data == "TOOLONG-DOITAGAIN" )
                setTimeout("longPolling()", 0 );
            else
                addLongPollingError("error", "Error on server side. Received data: \"" + data + "\"");
        },
        error: function(XMLHttpRequest, textStatus, errorThrown){
            isPolling--;
            addLongPollingError("error", textStatus + " (" + errorThrown + ")");
        }
    });
}

$(document).ready(function(){
    longPolling(); // Start the initial request 
});

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License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

CoperNick
Software Developer
Poland Poland
I graduated from the Jagiellonian University. After defence of master thesis (link to presentation) I have started professional programming in C and C++ using OpenGL. After that, my Company gave me a chance to switch to .Net framework and C# and I have betrayed my passion for computer graphics. Now I'm C#, SQL and sometimes ASP.NET programmer.

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