How to implement badges?

Question

I've given some thought to implementing badges (just like the badges here on Stack Overflow) and think it would be difficult without Windows services, but I'd like to avoid that if possible.

I came up with a plan to implement some examples:

• Audobiographer: Check if all fields in the profile is filled out.
• Commentor: When making a comment check if the number of comments equal 10, if so award the badge.
• Good Answer: When voting up check to see if vote score is 25 or higher.

How could this be implemented in the database? Or would another way be better?

Answer 1

Jobs. That is the key. Out of process jobs that run at set intervals to check the criteria that you mention. I don't think you even need to have a windows service unless it requires some external resources to set the levels. I actually think StackOverflow uses jobs as well for their calculations.

Answer 2

You could use triggers and check upon update or insert, then if your conditions are met add badge. That would handle it pretty seem less. Commence the trigger bashing in 3, 2, 1...

Answer 3

comments must be stored within the database right? then i think there are two main ways to do this.

1) when a user logs in you get a count of the comments. this is obvisously not the desired approach as the count could take a lot of time

2) when a user posts a comment you could either do a count then and store the count with the use details or you could do a trigger which executes when a comment is added. the trigger would then get the details of the newly created comment, grab the user id, get a count and store that against the user in a table of some sort.

i like the idea of a trigger as your program can return w/out waiting for sql server to do its stuff.

Answer 4

A similar-to-Stackoverflow implementation is actually a lot simpler than you have described, based on bits of info dropped by the team every once in awhile.

In the database, you simply store a collection of BadgeID-UserID pairs to track who has what (and a count or a rowID to allow multiple awards for some badges).

In the application, there is a worker object for each badge type. The object is in cache, and when the cache expires, the worker runs its own logic for determining who should get the badge and making the updates, and then it re-inserts itself into the cache:

public abstract class BadgeJob
{
    protected BadgeJob()
    {
        //start cycling on initialization
        Insert();
    }

    //override to provide specific badge logic
    protected abstract void AwardBadges();

    //how long to wait between iterations
    protected abstract TimeSpan Interval { get; }

    private void Callback(string key, object value, CacheItemRemovedReason reason)
    {
        if (reason == CacheItemRemovedReason.Expired)
        {
            this.AwardBadges();
            this.Insert();
        }
    }

    private void Insert()
    {
        HttpRuntime.Cache.Add(this.GetType().ToString(),
            this,
            null,
            Cache.NoAbsoluteExpiration,
            this.Interval,
            CacheItemPriority.Normal,
            this.Callback);
    }
}

And a concrete implementation:

public class CommenterBadge : BadgeJob
{
    public CommenterBadge() : base() { }

    protected override void AwardBadges()
    {
        //select all users who have more than x comments 
        //and dont have the commenter badge
        //add badges
    }

    //run every 10 minutes
    protected override TimeSpan Interval
    {
        get { return new TimeSpan(0,10,0); }
    }
}