Understanding Asp.net Cache Sliding Expiration and Absolute Expiration

Asp .Net provides two different ways to expire the cache on the basis of time. Here are two aproaches:-
  1. Sliding Expiration
  2. Absolute Expiration 
1. Absolute Expiration
Absolute expiration means that your data will be removed from cache after fixed amount of time either it is accessed or not. Generally we use it when we are displaying data which is changing but we can afford to display outdated data in our pages.  Mostly I put all of my dropdown values in cache with Absolute Expiration. Here is how you can code:-
DataTable dt = GetDataFromDatabase();
Cache.Insert("AbsoluteCacheKey", dt, null,
DateTime.Now.AddMinutes(1), //Data will expire after 1 minute
System.Web.Caching.Cache.NoSlidingExpiration);

2. Sliding Expiration
Sliding expiration means that your data will be removed from cache if that is not accessed for certain amount of time. Generally we store that data in this cache mode which is accessed many time on certain occasions. For example if you go in account settings section of a site, then you will be frequently accesing account information in that section. But most of the time you wont be using account setting's related data so there is no point of storing that data in cache. In such scenarios sliding expiration should be used. here is how you can save data in cache with sliding expiration:-

DataTable dt = GetDataFromDatabase();

Cache.Insert("SlidingExpiration", data, null,

System.Web.Caching.Cache.NoAbsoluteExpiration,

TimeSpan.FromMinutes(1));//Data will be cached for 1 mins


Hopefully this information will be useful for you, feel free to share your feedback with me. Happy Coding !!!
Posted by Zeeshan Umar 32 comments
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Article of the Day, PageMethod - An Easier and Faster Approach for ASP.NET Ajax

On Sunday, Feb 20, 2011, my article 'PageMethod - An Easier and Faster Approach for ASP.NET Ajax' was selected as 'Article of the Day' at http://www.asp.net.


I also recommend to all of readers to do share useful articles on http://www.asp.net/community. Whenever you found an article which is interesting and can be useful for others.

Posted by Zeeshan Umar 1 comments
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How to Pass value from ASP.Net to Javascript

Many times we have to pass a value from server side (ASP.Net) to client side (java script) and many peoples ask this question that how we can accomplish this task. Here I am sharing some examples in which I will tell different approaches to send values from ASP.Net to javascript.

1- <%=%> Construct
You can simply use a <%=%> construct to pass server side variable to client side. Here is how you can do this:-
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    
    </div>
    </form>
</body>
</html>
<script type="text/javascript">
    var myVariable = '<%=ServerSideVariable %>';
    alert(myVariable);
</script>

Here is the server side code in which I assigned value to my variable:-
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page
{
    public string ServerSideVariable { get; set; }
    protected void Page_Load(object sender, EventArgs e)
    {
        ServerSideVariable = "Zeeshan Umar";
    }
}

Here is the output when I run the page, a popup appears saying 'Zeeshan Umar'.

2) Hidden Field
You can also use hidden fields to store values which can be used in javascript here is how you can do this:-
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:HiddenField ID="hfValueFromServer" runat="server" />
    </div>
    </form>
</body>
</html>
<script type="text/javascript">
    var valueFromServer= document.getElementById('<%=hfValueFromServer.ClientID%>').value;
    alert(valueFromServer);
</script>

Here is the server side code in which I assigned value to hidden field:-
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        hfValueFromServer.Value = "Zeeshan Umar javascript tutorial";
    }
}

And here is the output of above code, same as expected 'Zeeshan Umar javascript tutorial':-

See how simple is it to access server side variables in javascript. Do share me with your valuable feedback and comments. Happy coding !!
Posted by Zeeshan Umar 1 comments
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How to end session when browser is closed

In high traffic sites sessions are very costly and they use lots of server's memory. Generally session timeout is 20 min (by default) and even if user closes the browser. Values in session still exist until session get expired after timeout. We can save lots of server memory if we destroy session as user closes the browser.

Here is how you can do it:-

1)First create a page AutoLogOut.aspx and in Page_Load event write this code:-
protected void Page_Load(object sender, EventArgs e)
{
    Session.Abandon();
}

2- Then add following javascript code in your page or Master Page:-
<script type="text/javascript">
     var clicked = false;
    function CheckBrowser()
    {
        if (clicked == false)
        {
            //Browser closed
        }
        else
        {
            //redirected 
            clicked = false;
        }
    }
 
    function bodyUnload()
    {
        if (clicked == false)//browser is closed
        {
            var request = GetRequest();
            
            request.open("GET", "AutoLogOut.aspx", true);
            request.send();
        }
    }
 
    function GetRequest()
    {
        var request = null;
        if (window.XMLHttpRequest)
        {
            //incase of IE7,FF, Opera and Safari browser
            request = new XMLHttpRequest();
        }
        else
        {
            //for old browser like IE 6.x and IE 5.x
            request = new ActiveXObject('MSXML2.XMLHTTP.3.0');
        }
        return request;
    } 


3- Finally on your body tag add these event handlers:-


<body onunload="bodyUnload();" onclick ="clicked=true;>


Now when user closes the browser, it will close session on server. However I just like to highlight that this solution might not work 100% time as there are chances that when user close the browser, he is not connected to internet.



Feel free to share your comments on my post.










Posted by
Zeeshan Umar








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Real World Scenario: Object Writer






Recently in a project I was facing a bug which was very difficult to reproduce. So, I decided to log object with complete properties in a text file. This code can be really useful for those who want to solve bugs which only occurs very rarely.



Here is the code of my class which converts object into a string:-




public class ObjectWriter
{
    public static string GetObjectString(object obj)
    {
        StringBuilder sb = new StringBuilder(1024);
        sb.Append("Type: ");
        sb.AppendLine(obj.GetType().ToString());
 
        if (obj == null)
        {
            sb.AppendLine("Value: Null");
        }
        else
        {
            sb.AppendLine("-------------------------");
            var type = obj.GetType();
 
            foreach (var prop in type.GetProperties())
            {
                var val = prop.GetValue(obj, new object[] { });
                var valStr = val == null ? "" : val.ToString();
                sb.AppendLine(prop.Name + ":" + valStr);
            }
        }
        return sb.ToString();
    }
}




Here is sample output and usage of my code:-






In above image I have called ObjectWriter.GetObjectString(ie) and in result varibale you can see that I can see its type and other fields information. You can write this information in log file for further investigation.









Posted by
Zeeshan Umar








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