How can I cache a function in asp.net

Question

Hi, I have a function which calculates distance from database records. This function is called at least twice in one asp.net page request. In this time period the result does not change. So what to do to cache result, I need performance in my app.

For example:

public static int GetKilometers(int VehicleID)
{ /*some db query and calculations*/ }

Answer 1

save in session with an if-condition if it definitely doesn't change

if(Session["functionresult"] == null)
{
    Session["functionresult"] = functionResult;
}

Answer 2

For a quick and easy solution, you can use the HttpContext.Session object to store a value like this:

int distance;
if(Session["distance"] == null)
{
    distance = GetKilometers(vehicleId);
    Session["distance"] = distance;
}
else
{
    distance = Convert.ToInt32(Session["distance"]);
}

To make it even easier, you can abstract this into its own method.

EDIT

The above solution is good for a minimal amount of data. Given the fact that there will be a LOT of data being stored in your case, I see two possible scenarios:

The calculated data for a vehicle X is different for each user
Cache the calculated data in a separate table in the database with UserId (or SessionId), VehicleId, and CalculatedData.

The calculated data for vehicle X is the same for any user that needs vehicle X's data
Cache that calculated data in a column in the vehicle table in the database.

Either way, your call to the database should retrieve data for all vehicles that the user needs for the current request. Then store that data in a local variable that lives only for the current request. If you're going to cache data by session, you can use HttpContext.Session to store the SessionId and use that to retrieve the data from the database.

Answer 3

If there are that many calculations, than using Session will eat up your server memory. You could use ViewState, but that would make your page pretty heavy.

Is it possible not to hit the db? Or minimize the number of round trips to the db.

Something like:

public static int GetKilometers(int[] VehicleID) { /* get all the data in one go */ }

Answer 4

If you're only concerned about the result in the lifetime of one page request (as you mention in your question), a simple local variable will suffice:

private int? _dist;

public int GetKilometers(int VehicleID)
{ 
    if (_dist == null) {
        _dist = /*some db query and calculations*/ 
    }
    return _dist;
}

This would prevent any memory concerns from excessive caching, but still allow some efficiency by not calculating the data twice for the same request.

One note is that you probably don't want this static, as that will cache the result across multiple users of your application.

Answer 5

From the OP's question all of these answers are useful and the syntax is the same but the wrong collections are being used. The proper collection for this is HttpContext.Current.Items. Combine this with the answer from @Aaron