Tag Archive for ‘database’ at Master Baboon

I wrote a simple game to learn how to store on and retrieve data from a server-side database. The rules are simple: you have to guess 2/3 of the average of the guesses of all the players. So, for example, if you think that the other players guessed on average 100, your guess should be 67. The 2/3 rule is there to avoid the trivial strategy of submitting the same number over and over again. According to game theory, the game has a Nash equilibrium at 0, which in this case does not correspond to a rational strategy. Wikipedia has some information and links about the game. Give it a try:

The score you see after submitting is the distance from your guess to the true 2/3 of the average. Since you get some information about your and others’ score, it should be possible to find a strategy to win in a small number of trials… Let me know if you find one!

Communicating with the server

To implement the game, I created a MySQL table in a database on the server that is used to store the players’ name and guess. The database is accessed by calling a server-side PHP script from the game Actionscript client.

The PHP script gets the player’s information and stores it in the database; then it computes the 2/3 of the average of all entries, and returns the score and rank of the current player, along with the top scores in the database. The script receives the data as a HTTP request (the ?var1=value1&var2=value2 thing you see in many dynamical web pages), and returns an XML fragment.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
\n";

// top scores

while (($row = mysql_fetch_array($hit)) &amp;&amp; ($currentrank==0 || $rank&lt;=$ntop)) {

  if ($rank&lt;=$ntop) {

    print "\n";

    print "\t{$row['name']}\n";

    print "\t{$row['diff']}\n";

    print "\n";

  }

  if ($row['time'] == $time) {

    $currentrank = $rank;

    $currentscore = $row['diff'];

  }

  $rank = $rank + 1;

}



// current score

print "\n\t{$name}\n\t{$currentscore}\n";

print "



\n";



mysql_close();



?&gt;

Calling the script from AS3 is relativelty easy. The remote call is done by a URLLoader object; the actual request is stored in a URLRequest object, and the request variables are wrapped in a URLVariables instance. I had an annoying problem with testing the code: for some reason, Flash always caches the requests. I looked around and it seems that the only workaround is to add a dummy variable to the request with a value that changes constantly, e.g., the current time.

This is the code for the communication with the server:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
public function submitGuess(name:String, guess:uint, ntop:int):void {

    var request:URLRequest = new URLRequest("http://www.masterbaboon.com/php/guess23/guess23submit.php");

    var httpHeader : URLRequestHeader = new URLRequestHeader("pragma", "no-cache");

    request.requestHeaders.push(httpHeader);



    // request variables: name of player, guess, number of top scores to return

    var vars:URLVariables = new URLVariables();

    vars.name = name;

    vars.guess = guess;

    vars.ntop = ntop;

    // this is to trick AS3 into not caching the URL request

    vars.nocache = Number(new Date().getTime());



    request.method = URLRequestMethod.GET;

    request.data = vars;



    // send to server and call loadingComplete when complete

    var loader:URLLoader = new URLLoader();



    // the results of the request is not returned immediately, but

    // we can monitor the COMPLETE event dispatched by the loader

    loader.addEventListener(Event.COMPLETE, loadingComplete);

    try {

        loader.load(request);

    } catch (e:Error) {

        trace("An error has occurred while communicating with the server.");

        trace(e);

    }

}



public function loadingComplete(e:Event):void {

    // this is how to access the data returned from the request

    data = XML(e.target.data);

    // switch frame

    gotoAndStop("highScoreFrame");

}

You’re welcome to download the whole code.

Master Baboon