Question

I am trying to implement caching in my program. I have a web application that provides user access to some learning courses.When the user logs on I authenticate him from our database. Now, if access a different course from the list I don’t want to go back to the database. Instead I want to store the value in cache for lets say 20 mins. The program should
1) Authenticate the user, and let him access the course. If he changes the course the program should look in cache. if the user id exists let him access the course without going back to server.
2) Provide a mechanism, that if after 20 minutes the user is still on the system, automatically update the time.so, that the user is not logged off.
I tried something like this

Cache ch = new Cache();
ch.Add("key","value);

but I get null refernece exception in 2nd statement. I have never worked with caching before so will appreciate any pointers.

Answer 1

Well this is how I use it:

/// <summary>
/// Get Data
/// </summary>
/// <returns>data</returns>
public static ElementOut GetData()
{
    //function return value
    ElementOut functionReturnValue = new ElementOut();

    try
    {
        string key = "data";
        if (HttpRuntime.Cache[key] == null)
        {
            //fetch data
            var data = CreateBLLAdapter().GetData();

            //validate data
            if (data == null) throw new Exception("data is empty!");

            //set cache to 12 hours
            DateTime timeToExpire = DateTime.Now.AddHours(12);

            //set cache
            HttpRuntime.Cache.Insert(key, data, null, timeToExpire, Cache.NoSlidingExpiration);
        }

        //set return from cache
        functionReturnValue = (ElementOut)HttpRuntime.Cache[key];

    }
    catch (Exception ex)
    {
        //Log.WriteServerErrorLog(ex);
    }

    return functionReturnValue;
}