Making JavaScript Applications Degrade Gracefully with AJAX and MySQL

As I promised in the section that you just read, below I listed the full source code that corresponds to this database-driven application, in conjunction with the output generated by it, naturally using the database records that you saw previously.

Here is the complete source code for this application:

(definition of "fetchrows.php" file)

<?php
// define 'MySQL' class
class MySQL{
   private $conId;
   private $host;
   private $user;
   private $password;
   private $database;
   private $result;
   const OPTIONS=4;
   public function __construct($options=array()){
     if(count($options)!=self::OPTIONS){
       throw new Exception('Invalid number of connection
parameters');
     }
     foreach($options as $parameter=>$value){
       if(!$value){
         throw new Exception('Invalid parameter '.$parameter);
       }
       this->{$parameter}=$value;
     }
     $this->connectDB();
   }
   // connect to MySQL
   private function connectDB(){
     if(!$this->conId=mysql_connect($this->host,$this-
>user,$this->password)){
       throw new Exception('Error connecting to the server');
     }
     if(!mysql_select_db($this->database,$this->conId)){
       throw new Exception('Error selecting database');
     }
   }
   // run query
   public function query($query){
     if(!$this->result=mysql_query($query,$this->conId)){
       throw new Exception('Error performing query '.$query);
     }
     return new Result($this,$this->result);
   }
}
// define 'Result' class
class Result {
   private $mysql;
   private $result;
   public function __construct(&$mysql,$result){
     $this->mysql=&$mysql;
     $this->result=$result;
   }
   // fetch row
   public function fetchRow(){
     return mysql_fetch_assoc($this->result);
   }
   // count rows
   public function countRows(){
     if(!$rows=mysql_num_rows($this->result)){
       throw new Exception('Error counting rows');
     }
     return $rows;
   }
   // count affected rows
   public function countAffectedRows(){
     if(!$rows=mysql_affected_rows($this->mysql->conId)){
       throw new Exception('Error counting affected rows');
     }
     return $rows;
   }
   // get ID form last-inserted row
   public function getInsertID(){
     if(!$id=mysql_insert_id($this->mysql->conId)){
       throw new Exception('Error getting ID');
     }
     return $id;
   }
   // seek row
   public function seekRow($row=0){
     if(!is_int($row)||$row<0){
       throw new Exception('Invalid result set offset');
     }
     if(!mysql_data_seek($this->result,$row)){
       throw new Exception('Error seeking data');
     }
   }
}
try{
   // connect to MySQL
   $db=new MySQL(array('host'=>'localhost','user'=>'user',
'password'=>'password','database'=>'database'));
   $result=$db->query("SELECT id,title,author FROM articles");
   echo '<h2>Article List</h2><div id="articlecontainer">';
   while($row=$result->fetchRow()){
     echo '<div id="article'.$row['id'].'">';
     echo 'Title: '.$row['title'].'<br /> Author: '.$row
['author'].'<a href="showdetail.php?id='.$row['id'].'"> Read
more</a>';
     echo'</div><hr />';
   }
   echo '</div>';

}
catch(Exception $e){
   echo $e->getMessage();
   exit();
}
?>
<script language="javascript">
// send http requests
function sendHttpRequest(url,callbackFunc,respXml){
   var xmlobj=null;
   try{
     xmlobj=new XMLHttpRequest();
   }
   catch(e){
     try{
       xmlobj=new ActiveXObject("Microsoft.XMLHTTP");
     }
     catch(e){
       alert('AJAX is not supported by your browser!');
       return false;
     }
   }
   xmlobj.onreadystatechange=function(){
     if(xmlobj.readyState==4){
       if(xmlobj.status==200){
         respXml?eval(callbackFunc+'(xmlobj.responseXML)'):eval
(callbackFunc+'(xmlobj.responseText)');
       }
     }
   }
   // open socket connection
   xmlobj.open('GET',url,true);
   // send http header
   xmlobj.setRequestHeader('Content-Type','text/html;
charset=UTF-8');
   // send http request
   xmlobj.send(null);
}
function showDetails(results){
   if(results){
     var divid=results.split('|')[0];
     var result=results.split('|')[1];
     var artdiv=document.getElementById('article'+divid);
     if(divid){
       var div=document.createElement('div');
       div.appendChild(document.createTextNode(result));
       artdiv.appendChild(div);
     }
   }
}
var artcont=document.getElementById('articlecontainer');
if(artcont){
  var links=artcont.getElementsByTagName('a');
  if(links){
    for(var i=0;i<links.length;i++){
      links[i].onclick=function(){
        sendHttpRequest('showdetail.php?id='+this.href.split('?')
[1].substring(3),'showDetails');
        this.href='#';
      }
    }
  }
}
</script>

(definition of "showdetails.php" file)

<?php

// define 'MySQL' class
class MySQL{
   private $conId;
   private $host;
   private $user;
   private $password;
   private $database;
   private $result;
   const OPTIONS=4;
   public function __construct($options=array()){
     if(count($options)!=self::OPTIONS){
       throw new Exception('Invalid number of connection
parameters');
     }
     foreach($options as $parameter=>$value){
       if(!$value){
         throw new Exception('Invalid parameter '.$parameter);
       }
       $this->{$parameter}=$value;
     }
     $this->connectDB();
   }
   // connect to MySQL
   private function connectDB(){
     if(!$this->conId=mysql_connect($this->host,$this-
>user,$this->password)){
       throw new Exception('Error connecting to the server');
     }
     if(!mysql_select_db($this->database,$this->conId)){
       throw new Exception('Error selecting database');
     }
   }
   // run query
   public function query($query){
     if(!$this->result=mysql_query($query,$this->conId)){
       throw new Exception('Error performing query '.$query);
     }
     return new Result($this,$this->result);
   }
}
// define 'Result' class
class Result {
   private $mysql;
   private $result;
   public function __construct(&$mysql,$result){
     $this->mysql=&$mysql;
     $this->result=$result;
   }
   // fetch row
   public function fetchRow(){
     return mysql_fetch_assoc($this->result);
   }
   // count rows
   public function countRows(){
     if(!$rows=mysql_num_rows($this->result)){
       throw new Exception('Error counting rows');
     }
     return $rows;
   }
   // count affected rows
   public function countAffectedRows(){
     if(!$rows=mysql_affected_rows($this->mysql->conId)){
       throw new Exception('Error counting affected rows');
     }
     return $rows;
   }
   // get ID form last-inserted row
   public function getInsertID(){
     if(!$id=mysql_insert_id($this->mysql->conId)){
       throw new Exception('Error getting ID');
     }
     return $id;
   }
   // seek row
   public function seekRow($row=0){
     if(!is_int($row)||$row<0){
       throw new Exception('Invalid result set offset');
     }
     if(!mysql_data_seek($this->result,$row)){
       throw new Exception('Error seeking data');
     }
   }
}
try{
   // connect to MySQL
   $db=new MySQL(array('host'=>'host','user'=>'user',
'password'=>'password','database'=>'database'));
   $id=$_GET['id'];
   $result=$db->query("SELECT content FROM articles WHERE
id='$id'");
   while($row=$result->fetchRow()){
     echo $id.'|'.$row['content'];
   }
}
catch(Exception $e){
   echo $e->getMessage();
   exit();
}
?>

As you can see, now the full contents of a concrete article are displayed on the same web page that shows the articles' tiles and authors respectively. Of course it will happen this way only if JavaScript is enabled on the browser. Otherwise, users still will be able to see the content, but on a different web document.

Final thoughts

Finally, we've come to the end of this series. I hope that you analyze in detail all the practical examples shown here, so you can use them as a source of inspiration for creating JavaScript applications that degrade gracefully.

See you in the next web development tutorial!