Data Exchange with XML, WDDX and PHP - Money Talks
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Let's try another example, this one using WDDX to transmit five-day currency rate data to a requesting client. The client then uses this data to calculate an average rate for the past five days.
Let's assume that the data is stored in the following database table:
mysql> select * from currency;
+--------+-------+-------+-------+-------+-------+
| symbol | mark1 | mark2 | mark3 | mark4 | mark5 |
+--------+-------+-------+-------+-------+-------+
| GBP | 0.72 | 0.69 | 0.73 | 0.75 | 0.69 |
| INR | 0.023 | 0.045 | 0.012 | 0.019 | 0.025 |
| DZD | 0.01 | 0.009 | 0.015 | 0.011 | 0.01 |
| CAD | 0.66 | 0.65 | 0.68 | 0.7 | 0.64 |
| DEM | 0.43 | 0.44 | 0.43 | 0.42 | 0.42 |
+--------+-------+-------+-------+-------+-------+
5 rows in set (0.00 sec)
The server script needs to get all five values and encode them as a WDDX packet.
<?
// server.php - output WDDX packet containing currency data// database parameters$hostname = "medusa";$user = "wddx_agent";$pass = "jser745mf";$database = "trends";// open connection to database$connection = mysql_connect($hostname, $user, $pass) or die ("Unable toconnect!");// get rates for last five days$query = "SELECT mark1, mark2, mark3, mark4, mark5 FROM currency WHEREsymbol = '$symbol'";$result = mysql_db_query($database, $query, $connection) or die ("Error inquery: $query. " . mysql_error());// add data to packetif (mysql_num_rows($result) > 0) { $mark = mysql_fetch_row($result); }mysql_close($connection);// print packetecho wddx_serialize_value($mark);?>
Again, the array of five values is encoded as a WDDX packet, and sent to the requesting client, which decodes it and prints the data, together with an average of all five values.
<?
// client.php - connect to server, retrieve and decode WDDX packet// url of Web page$url = "http://medusa/server.php?symbol=$symbol";// read WDDX packet into string$package = join ('', file($url));// deserialize$rates = wddx_deserialize($package);?><html><head><basefont face="Verdana"></head><body><h3>Five-day currency trends for currency symbol <? echo $symbol; ?></h3><table border="1" cellspacing="3" cellpadding="3"><tr><td>Data pointer 1</td><td>Data pointer 2</td><td>Data pointer 3</td><td>Data pointer 4</td><td>Data pointer 5</td><td>Average</td></tr><tr><?$sum = 0;// print rate datafor($x=0; $x<5; $x++){ $sum = $sum + $rates[$x]; echo "<td>$rates[$x]</td>";}// calculate average$avg = $sum/5;echo "<td>$avg</td>";?></tr></table></body></html>
Simple, huh?
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