Completing the refactoring process: building the paging links - PHP

In the third part of his series, Alejandro Gervasio digs a bit further into object-oriented PHP. He explains the barebones of a paging class and techniques used to aggregate a new “MySQLConnector” class.

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By: Alejandro Gervasio

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June 08, 2005

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If I could chose between the different parts of the method, I’d say that this one is the easiest to grasp. This section provides the essentials to create the paging links, as the final task to complete the refactoring process. While the technique that we’re using here to generate the links has been strongly documented in previous articles, it deserves a quick explanation.

Since the method has generated the output containing values from database records, it creates the paging links by packaging them into a single <div> element. The code to build the links is listed below:

$this->output.='<div>';
// create previous link
if($page>1){
    $this->output.='<a href="'.$_SERVER['PHP_SELF'].'?
    page='.($page-1).'"><<Previous</a> ';
}
// create numbered links
for($i=1;$i<=$numPages;$i++){
    ($i!=$page)?$this->output.='<a href="'.$_SERVER
    ['PHP_SELF'].'?page='.$i.'">'.$i.'</a>
     ':$this->output.=$i.' ';
}
// create next link
if($page<$numPages){
    $this->output.=' <a href="'.$_SERVER
    ['PHP_SELF'].'?page='.($page+1).'">Next>></a> ';
}
$this->output.='</div>';
// return generated output
return $this->output;

Notice here that the use of the $page pointer is very relevant. We first check if it’s possible to create a <previous> link, determining if we’re not placed in the first page ($page>1). If this condition is true, we simply append that link to the final output, like this:

if($page>1){
$this->output.='<a href="'.$_SERVER['PHP_SELF'].'?
page='.($page-1).'"><<Previous</a> ';
}

Later, using a regular loop, we create the numbered links, as follows:

for($i=1;$i<=$numPages;$i++){
    ($i!=$page)?$this->output.='<a href="'.$_SERVER
    ['PHP_SELF'].'?page='.$i.'">'.$i.'</a>
     ':$this->output.=$i.' ';
}

Finally, after the numbered link creation, we'll check if a <next> link is feasible of being appended. If it is, then we append it to the code and return the whole output for further processing:

$this->output.='</div>';
// return generated output
return $this->output;

Great! Didn’t I tell you that this was the easiest part of the method? At this point, the method is fully functional, since it’s scoped the two core processes involved in dynamic output generation: paged record visualization and paging link creation, using the benefits added by our friendly “MySQLConnector” object.

As usual, if you want to take a look at the full code for this class and implement it in your own projects, here it is:

class Pager {
    var $db; // MySQLConnector object
    var $query; // SQL query
    var $numRecs; // number of records per page
    var $output=''; // dynamic output
    function Pager(&$db,$query,$numRecs=5){
        $this->db=&$db;
        (preg_match("/^SELECT/",$query))?
        $this->query=$query:die('Invalid query '.$query);
        (is_int($numRecs)&&$numRecs>0)?
        $this->numRecs=$numRecs:die('Invalid number of
        records');
    }
    function displayRecords($page){
    // calculate total number of records using MySQLConnector object
    if(!$totalRecs=$this->db->getNumRows
    ($this->db->performQuery($this->query))){
        die('Cannot retrieve records from database');
    }
    // calculate number of pages
    $numPages=ceil($totalRecs/$this->numRecs);
    // validate page pointer $page
    if(!preg_match("/^\d{1,2}$/",$page)
    ||$page<1||$page>$numPages){
        $page=1;
    }
    // retrieve result set using MySQLConnector object
    $this->db->performQuery($this->query.' LIMIT '.
    ($page-1)*$this->numRecs.','.$this->numRecs);
    while($rows=&$this->db->fetchRow()){
        foreach($rows as $row){
            $this->output.=$row.' ';
            }
        $this->output.='<br />';
        }
    $this->output.='<div>';
    // create previous link
    if($page>1){
        $this->output.='<a href="'.$_SERVER['PHP_SELF'].'?
        page='.($page-1).'"><<Previous</a> ';
        }
    // create numbered links
    for($i=1;$i<=$numPages;$i++){
    ($i!=$page)?$this->output.='<a href="'.$_SERVER
    ['PHP_SELF'].'?page='.$i.'">'.$i.'</a>
     ':$this->output.=$i.' ';
    }
    // create next link
    if($page<$numPages){
        $this->output.=' <a href="'.$_SERVER
        ['PHP_SELF'].'?page='.($page+1).'">Next>></a>
         ';
        }
    $this->output.='</div>';
    // return generated output
    return $this->output;
    }
}

To Wrap Things Up...

In this third part of the series, I’ve offered a full coverage about how Aggregation can be implemented on PHP applications, showing two classes often used in Web-related projects: a MySQL database abstraction class and a dynamic paging class, this way highlighting the necessary key concepts to translate the underlying theory in a practical usage. So, now the relevant question is: what’s next? In the final article of this four-part series, we’ll get more practical, showing a concrete example to, hopefully see in action both classes. Now that you’ve tasted the power of aggregation, go and put it to work for you!